# gemmology.dev

> Open, FGA-aligned reference and study toolkit for coloured gemstones. Free and open-source. Reference data covers 121 mineral families (natural, synthetic, simulant, composite) and 171 crystal expressions; the curriculum is structured around the Fellowship of the Gemmological Association (FGA) Diploma syllabus.

## Core surfaces
- [Home](https://gemmology.dev/): Project overview, mineral counts, calculator entry points.
- [Mineral gallery](https://gemmology.dev/gallery/): Browse all 303 mineral pages with crystal SVGs rendered from Miller indices.
- [Learn hub](https://gemmology.dev/learn/): 138 curriculum-aligned articles across 8 categories (fundamentals, equipment, species, identification, phenomena, origin, market, care).
- [Quiz & exam](https://gemmology.dev/quiz/): Spaced-repetition practice and timed FGA-style exam mode covering the same 8 categories.
- [Tools hub](https://gemmology.dev/tools/): Six categories of gemmological calculators and reasoners — measurement, optical, lab, identification, advanced, conversions.
- [CDL specification](https://gemmology.dev/docs/cdl/): Crystal Description Language v2 reference (the notation used for all crystal morphology data).
- [API reference](https://gemmology.dev/docs/api/cdl-parser/): Python package APIs for cdl-parser, crystal-geometry, mineral-database, crystal-renderer, cdl-lsp.
- [About](https://gemmology.dev/about/): Editorial standards, sourcing, contributor information.

## Tools

- [Tools hub](https://gemmology.dev/tools/): Index of all six tool categories.
- [Measurement](https://gemmology.dev/tools/measurement/): Specific gravity (hydrostatic + water-temp corrected), refractometer lookup, birefringence, critical angle, carat estimator (with girdle correction), Hanneman/Hodgkinson over-the-limit RI.
- [Optical](https://gemmology.dev/tools/optical/): Dichroscope results, polariscope guide, refractometer simulator (with OTL behaviour), pleochroism reasoner, optic sign / 2V reasoner.
- [Lab](https://gemmology.dev/tools/lab/): Spectroscope calculator and reverse band-matcher against a 16-species absorption-band table, UV fluorescence lookup (LWUV/SWUV/phosphorescence).
- [Identification](https://gemmology.dev/tools/identification/): Filtered gemstone identifier — narrow against species using RI, SG, birefringence, hardness, dispersion, optical character.
- [Advanced](https://gemmology.dev/tools/advanced/): Evidence-weighted treatment-detection wizard (18 clues x 11 treatments), treatment reference table, proportion analyzer with GIA cut-grade overlay for round brilliants.
- [Conversions](https://gemmology.dev/tools/conversions/): Carat/gram/milligram weight converter, length and temperature converters used in gemmological measurement workflows.

## Learn

### Fundamentals
- [Crystal Systems](https://gemmology.dev/learn/fundamentals/crystal-systems): The seven crystal systems and their characteristic symmetry elements.
- [Advanced Crystallography](https://gemmology.dev/learn/fundamentals/crystallography-advanced): Twinning, Miller indices, crystal habits, crystal forms, point groups, and crystal growth mechanisms.
- [Twin Laws in Gemmology](https://gemmology.dev/learn/fundamentals/twin-laws): Named twin laws — spinel, Carlsbad, Manebach, Baveno, albite, pericline, Brazil, Dauphiné, Japan — and corundum parting, with diagnostic applications.
- [Physical Properties](https://gemmology.dev/learn/fundamentals/physical-properties): Hardness, specific gravity, cleavage, fracture, and lustre.
- [Chemical Properties](https://gemmology.dev/learn/fundamentals/chemical-properties): Gem chemistry, chromophores and colour causes, allochromatic vs idiochromatic minerals, charge transfer, and colour centres.
- [Optical Properties](https://gemmology.dev/learn/fundamentals/optical-properties): Refractive index, birefringence, pleochroism, dispersion, and other optical properties of gemstones.
- [Colour Theory in Gemmology](https://gemmology.dev/learn/fundamentals/colour-theory): The physics and chemistry of gem colour — crystal field theory, charge transfer, colour centres, allochromatic and idiochromatic minerals, and band-gap colouration.
- [Advanced Optical Properties](https://gemmology.dev/learn/fundamentals/optical-properties-advanced): Interference figures, optic sign determination, complete absorption spectra, luminescence, and anomalous double refraction.
- [Optic Sign Determination](https://gemmology.dev/learn/fundamentals/optic-sign-determination): Determining positive or negative optic sign for uniaxial and biaxial gems using the refractometer, lambda plate, and interference figures.

### Equipment
- [Gem Testing Equipment Overview](https://gemmology.dev/learn/equipment/overview): Introduction to gemmological instruments, testing workflow, and which tool to use for different identification tasks.
- [The Refractometer](https://gemmology.dev/learn/equipment/refractometer): Refractive index measurement using the gemmological refractometer, including faceted and cabochon techniques, birefringence reading, and troubleshooting.
- [The Polariscope](https://gemmology.dev/learn/equipment/polariscope): Using the polariscope to determine optic character (isotropic vs anisotropic), detect anomalous double refraction, and observe interference figures.
- [The Dichroscope](https://gemmology.dev/learn/equipment/dichroscope): Using the dichroscope to observe pleochroism in coloured gemstones, distinguishing dichroic from trichroic materials.
- [The Spectroscope](https://gemmology.dev/learn/equipment/spectroscope): Using the spectroscope to observe absorption spectra, identifying characteristic patterns for gem species and detecting treatments.
- [The Microscope](https://gemmology.dev/learn/equipment/microscope): Using the gemmological microscope for inclusion study, illumination techniques, and immersion methods to identify gems and detect treatments.
- [The UV Lamp](https://gemmology.dev/learn/equipment/uv-lamp): Using ultraviolet light for fluorescence testing, distinguishing LWUV from SWUV reactions, and safety considerations.
- [Other Testing Tools](https://gemmology.dev/learn/equipment/other-tools): Chelsea filter, thermal conductivity probes, specific gravity measurement, and other supporting gemmological instruments.
- [Chelsea Colour Filter](https://gemmology.dev/learn/equipment/chelsea-colour-filter): Using the Chelsea Colour Filter as a chromium discriminator for gem identification — including the species reaction table, lighting requirements, and diagnostic limitations.
- [Specific Gravity Measurement](https://gemmology.dev/learn/equipment/sg-measurement): Hydrostatic weighing and heavy-liquid methods for measuring specific gravity – the density-based property used to identify and confirm gem species.
- [Conoscopic Observation and Interference Figures](https://gemmology.dev/learn/equipment/conoscope): Using convergent polarised light to observe interference figures that reveal a gemstone's optic character (uniaxial or biaxial) and optic sign – an advanced polariscope technique.
- [Advanced Laboratory Instruments](https://gemmology.dev/learn/equipment/advanced-lab-instruments): Diploma-level awareness of FTIR, UV-Vis-NIR, Raman, EDXRF, LA-ICP-MS, and photoluminescence spectroscopy — what each detects and its key gemmological applications.
- [Diamond Screening Instruments](https://gemmology.dev/learn/equipment/diamond-screening): Thermal conductivity probes, electrical conductivity testers, DiamondView, DiamondSure, and reflectance meters – the tools used to screen loose diamonds and detect synthetic and simulant materials.

### Species
- [Corundum](https://gemmology.dev/learn/species/corundum): Corundum species including ruby and sapphire varieties, properties, inclusions, origins, treatments, and historical significance.
- [Beryl](https://gemmology.dev/learn/species/beryl): Beryl species including emerald, aquamarine, morganite, heliodor, goshenite, and red beryl with properties, inclusions, and treatments.
- [Garnet Group](https://gemmology.dev/learn/species/garnet): The garnet group minerals including almandine, pyrope, spessartine, grossular, andradite, and their gem varieties like demantoid and tsavorite.
- [Tourmaline Group](https://gemmology.dev/learn/species/tourmaline): The tourmaline group including elbaite varieties (rubellite, indicolite, Paraíba), dravite, and chrome tourmaline with properties and identification.
- [Spinel](https://gemmology.dev/learn/species/spinel): Spinel species including red, blue, pink, and colour-change varieties with properties, origins, historical significance, and identification.
- [Topaz](https://gemmology.dev/learn/species/topaz): Topaz species including imperial, blue, sherry, and colourless varieties with properties, treatments, and identification.
- [Quartz](https://gemmology.dev/learn/species/quartz): Quartz species including amethyst, citrine, rose quartz, smoky quartz, rock crystal, and chalcedony varieties with properties and identification.
- [Feldspar Group](https://gemmology.dev/learn/species/feldspar): Feldspar group gems including moonstone, labradorite, sunstone, amazonite, and orthoclase with properties, phenomena, and identification.
- [Chrysoberyl](https://gemmology.dev/learn/species/chrysoberyl): Chrysoberyl species including alexandrite and cat's eye chrysoberyl (cymophane) with properties, colour change, chatoyancy, and identification.
- [Zircon](https://gemmology.dev/learn/species/zircon): Zircon species including blue, colourless, and fancy colours with metamict types, properties, treatments, and identification.
- [Olivine (Peridot)](https://gemmology.dev/learn/species/olivine): Olivine species and its gem variety peridot with properties, characteristic inclusions, sources, and identification.
- [Zoisite](https://gemmology.dev/learn/species/zoisite): Zoisite species including tanzanite, thulite, and anyolite with properties, colour change, treatments, and identification.
- [Diamond](https://gemmology.dev/learn/species/diamond): Diamond type classification, the 4Cs grading system, fancy colours, natural vs lab-grown identification, and diamond verification instruments.
- [Pyroxene Group](https://gemmology.dev/learn/species/pyroxene): Pyroxene group gems including jadeite, spodumene (kunzite, hiddenite), and diopside (chrome diopside) with properties and identification.
- [Amphibole Group (Nephrite)](https://gemmology.dev/learn/species/amphibole): Amphibole group gems, primarily nephrite jade, with properties, comparison to jadeite, sources, and identification.
- [Opal](https://gemmology.dev/learn/species/opal): Opal species including precious opal (black, white, crystal, boulder, fire) and common opal with play of colour, patterns, and identification.
- [Pearl](https://gemmology.dev/learn/species/pearl): Pearl formation, types (natural, Akoya, South Sea, Tahitian, freshwater), grading factors, identification, and care.
- [Coral](https://gemmology.dev/learn/species/coral): Precious coral species including red (ox blood), pink (angel skin), and related varieties with identification, treatments, and conservation.
- [Amber](https://gemmology.dev/learn/species/amber): Amber fossilised tree resin including Baltic, Dominican, and Burmese varieties with inclusions, identification, and distinguishing from copal.
- [Jet](https://gemmology.dev/learn/species/jet): Jet fossilised wood including Whitby jet, properties, Victorian significance, identification, and distinguishing from simulants.

### Identification
- [Beryllium Diffusion — Deep Diagnostic Reference](https://gemmology.dev/learn/identification/treatments-deep/beryllium-diffusion): Full per-method detection protocol for beryllium lattice diffusion in corundum, with disclosure standards and stability data.
- [Inclusions Overview](https://gemmology.dev/learn/identification/inclusions/overview): Introduction to inclusions, their classification, and microscopy techniques for examination.
- [Lead Glass-Filled Ruby — Deep Diagnostic Reference](https://gemmology.dev/learn/identification/treatments-deep/lead-glass-ruby): Full detection protocol for composite (lead glass-filled) ruby, with nomenclature, durability, and disclosure standards.
- [Solid Inclusions](https://gemmology.dev/learn/identification/inclusions/solid-inclusions): Crystal inclusions - identifying mineral guests trapped within gemstones during formation.
- [HPHT Diamond Treatment — Deep Diagnostic Reference](https://gemmology.dev/learn/identification/treatments-deep/hpht-diamond): Full detection protocol for HPHT-treated natural diamonds, including type-by-type outcomes, DiamondView patterns, and photoluminescence signatures.
- [Fluid Inclusions](https://gemmology.dev/learn/identification/inclusions/fluid-inclusions): Two-phase, three-phase, and negative crystal inclusions - trapped fluids that reveal formation conditions.
- [CVD Diamond Detection — Deep Diagnostic Reference](https://gemmology.dev/learn/identification/treatments-deep/cvd-diamond): Full detection protocol for CVD synthetic diamonds, distinguishing from natural and HPHT-treated stones using DiamondView, FTIR, and photoluminescence.
- [Growth Features](https://gemmology.dev/learn/identification/inclusions/growth-features): Colour zoning, growth tubes, twinning, phantoms, and other patterns formed during crystallization.
- [Gemstone Treatments](https://gemmology.dev/learn/identification/treatments): Heat treatment, filling, diffusion, coating, and detection methods for treated gemstones — with per-species diagnostic depth.
- [Feathers & Fingerprints](https://gemmology.dev/learn/identification/inclusions/feathers): Healed fractures, fingerprint inclusions, and liquid feathers - characteristic healing patterns in gems.
- [Synthetic Gemstones](https://gemmology.dev/learn/identification/synthetics): Synthetic gem production methods including flame fusion, hydrothermal, flux growth, and detection techniques.
- [Silk & Needle Inclusions](https://gemmology.dev/learn/identification/inclusions/silk): Rutile silk, needle inclusions, and their role in asterism and origin determination.
- [Natural vs Synthetic Indicators](https://gemmology.dev/learn/identification/inclusions/natural-vs-synthetic): Distinguishing natural gemstones from synthetics using inclusion evidence.
- [Surface Features](https://gemmology.dev/learn/identification/inclusions/surface-features): Naturals, bearding, etch channels, and other surface-related inclusion features.
- [Composite Stones](https://gemmology.dev/learn/identification/composite-stones): Doublets, triplets, assembled stones, and their detection including opal doublets, garnet-topped doublets, and soudé emeralds.

### Phenomena
- [Optical Phenomena Overview](https://gemmology.dev/learn/phenomena/overview): Introduction to optical phenomena in gemstones including light interaction principles and summary of major phenomena.
- [Asterism (Star Effect)](https://gemmology.dev/learn/phenomena/asterism): Asterism in gemstones including star ruby, star sapphire, and other star stones with formation, quality factors, and identification.
- [Chatoyancy (Cat's Eye Effect)](https://gemmology.dev/learn/phenomena/chatoyancy): Chatoyancy in gemstones including chrysoberyl cat's eye, the milk and honey effect, and other chatoyant gems.
- [Adularescence](https://gemmology.dev/learn/phenomena/adularescence): Adularescence in moonstone including cause, types of moonstone, quality factors, and distinction from labradorescence.
- [Labradorescence](https://gemmology.dev/learn/phenomena/labradorescence): Labradorescence in labradorite and spectrolite including cause, colour range, quality factors, and distinction from adularescence.
- [Play of Colour](https://gemmology.dev/learn/phenomena/play-of-colour): Play of colour in precious opal including cause, pattern types, body tones, and quality assessment.
- [Colour Change](https://gemmology.dev/learn/phenomena/colour-change): Colour change phenomenon in gemstones including alexandrite, colour-change garnet, sapphire, and diaspore with causes and grading.
- [Aventurescence](https://gemmology.dev/learn/phenomena/aventurescence): Aventurescence in gemstones including sunstone and aventurine quartz with causes, types, and quality factors.
- [Iridescence](https://gemmology.dev/learn/phenomena/iridescence): Iridescence in gemstones including fire agate, ammolite, iris quartz, and surface coatings with causes and identification.
- [Schiller and Peristerescence](https://gemmology.dev/learn/phenomena/schiller): Schiller and peristerescence in feldspar – the mechanism of non-spectral lamellar scattering, named species, and distinction from adularescence, labradorescence, aventurescence, and chatoyancy.
- [Silk Effect](https://gemmology.dev/learn/phenomena/silk-effect): The silk effect in Kashmir sapphire and Burmese ruby — velvety appearance from rutile-needle clouds, mechanism, distinction from asterism, and diagnostic significance for origin and heat-treatment detection.
- [Fluorescence and Phosphorescence](https://gemmology.dev/learn/phenomena/fluorescence): Fluorescence and phosphorescence in gemstones – Stokes shift mechanism, LWUV vs SWUV regimes, species reaction table, phosphorescence afterglow, and diagnostic applications for natural vs synthetic identification.
- [Fire and Dispersion](https://gemmology.dev/learn/phenomena/fire-dispersion): Fire in faceted gemstones — dispersion as differential refraction by wavelength, the B–G interval, named dispersion values, relationship to facet design, and distinction from diffraction-based spectral effects.
- [Pearl Orient](https://gemmology.dev/learn/phenomena/orient): Pearl orient – the soft iridescent surface bloom of fine nacre, arising from thin-film diffraction and interference at aragonite tablet layers, distinguished from body colour, lustre, and fluorescence.
- [Tenebrescence](https://gemmology.dev/learn/phenomena/tenebrescence): Tenebrescence – reversible photochromic colour change in hackmanite driven by S₂⁻ radical colour centres, mechanism, named species, and diagnostic distinction from the alexandrite effect and irradiation-induced colour changes.
- [Alexandrite Effect – Physical Mechanism](https://gemmology.dev/learn/phenomena/alexandrite-effect): Deep dive into the alexandrite effect – Cr³⁺ in trigonal crystal field, the dual transmission window, photopic peak balance, named species including garnets, sapphire, and synthetic spinel, and how to test colour change under standardised illuminants.

### Origin
- [Origin Determination Overview](https://gemmology.dev/learn/origin/overview): Introduction to geographic origin determination for gemstones including methodology, premium factors, and laboratory reports.
- [Afghanistan — Gem Origins Overview](https://gemmology.dev/learn/origin/afghanistan/overview): Hindu Kush gem province — lapis lazuli (Sar-e-Sang), Panjshir emerald, Nuristan kunzite; multiple geological settings; conflict and artisanal mining context.
- [Australian Gems - Overview](https://gemmology.dev/learn/origin/australia/overview): Introduction to Australia's gem production, world leadership in opal, and significant sapphire and chrysoprase deposits.
- [Brazilian Gems - Overview](https://gemmology.dev/learn/origin/brazil/overview): Introduction to Brazil's diverse gem production including Paraíba tourmaline, imperial topaz, aquamarine, and other varieties.
- [Burmese Gems - Overview](https://gemmology.dev/learn/origin/burma/overview): Introduction to Myanmar's legendary gem production from Mogok and other regions, including ethical considerations.
- [East African Gems - Overview](https://gemmology.dev/learn/origin/east-africa/overview): Introduction to East Africa's emergence as a major coloured gem region, covering Tanzania, Kenya, and Mozambique.
- [Madagascar Gems - Overview](https://gemmology.dev/learn/origin/madagascar/overview): Introduction to Madagascar's emergence as a major gem source and its diverse production of sapphire, ruby, and rare species.
- [Pakistan — Gem Origins Overview](https://gemmology.dev/learn/origin/pakistan/overview): Himalayan collision zone gem deposits — Swat emerald, Hunza ruby, Katlang topaz, Skardu aquamarine; multiple geological settings.
- [Russia — Ural Gem Deposits Overview](https://gemmology.dev/learn/origin/russia/overview): Ural Mountains gem belt — demantoid garnet, alexandrite, emerald; Yakutia diamond; serpentinite and mica-schist geological settings.
- [Thailand – Gem Origins Overview](https://gemmology.dev/learn/origin/thailand/overview): Southeast Asian gem province centred on Chanthaburi, Trat, Kanchanaburi, Bo Phloi, and Bo Rai; world leader in corundum heat treatment and trading.
- [USA – Gem Origins Overview](https://gemmology.dev/learn/origin/usa/overview): US gem deposits – Montana sapphire, Utah red beryl, Arizona peridot, California and Maine tourmaline; geologically diverse patchwork provinces.
- [Kashmir Sapphire](https://gemmology.dev/learn/origin/kashmir): Kashmir sapphire characteristics, diagnostic inclusions, velvety appearance, historical significance, and market premiums.
- [Lapis Lazuli — Sar-e-Sang, Afghanistan](https://gemmology.dev/learn/origin/afghanistan/lapis): Sar-e-Sang (Badakhshan) lapis lazuli — the canonical ancient-world source, >7,000 years of continuous mining, geochemical fingerprinting, grades and quality.
- [Lightning Ridge Black Opal](https://gemmology.dev/learn/origin/australia/black-opal): The world's most valuable opal from Lightning Ridge, NSW - body tone, patterns, and quality factors.
- [Paraíba Tourmaline](https://gemmology.dev/learn/origin/brazil/paraiba): Brazil's legendary copper-bearing tourmaline - discovery, neon colours, and its position as the most valuable tourmaline.
- [Burmese Ruby](https://gemmology.dev/learn/origin/burma/ruby): Mogok and Mong Hsu ruby - the pigeon blood standard, diagnostic inclusions, and comparison with other sources.
- [Tanzanite](https://gemmology.dev/learn/origin/east-africa/tanzanite): Tanzania's signature gemstone from the Merelani Hills - single-source rarity, colour grades, and heat treatment.
- [Madagascar Sapphire](https://gemmology.dev/learn/origin/madagascar/sapphire): Ilakaka sapphire region - characteristics, Ceylon comparison, diagnostic inclusions, and quality assessment.
- [Swat Valley Emerald — Pakistan](https://gemmology.dev/learn/origin/pakistan/emerald): Ophiolite-hosted Cr-rich emerald from Mingora, Swat Valley; three-phase fluid inclusions, chromian muscovite, low Li chemistry, talc-carbonate paragenesis.
- [Russian Demantoid Garnet — Ural Mountains](https://gemmology.dev/learn/origin/russia/demantoid): Ural demantoid (andradite, Cr-coloured); horsetail inclusions — byssolite terminology and Kissin 2021 mineralogical correction; LA-ICP-MS origin discrimination from Namibia and Madagascar.
- [Thai Ruby – Chanthaburi-Trat and Bo Rai Types](https://gemmology.dev/learn/origin/thailand/ruby): Basaltic-hosted Siam ruby from Chanthaburi-Trat and Bo Rai; diagnostic high-Fe chemistry, 451/460/470 nm iron triplet, weak fluorescence, alluvial habit.
- [Montana Sapphire — Yogo Gulch, Rock Creek, Missouri River](https://gemmology.dev/learn/origin/usa/montana-sapphire): Yogo Gulch steely-blue lamprophyre sapphire (no heat needed), Rock Creek and Missouri River alluvial pastels; distinct Fe/Ti/Mg trace element chemistry; US commercial significance.
- [Panjshir Emerald – Afghanistan](https://gemmology.dev/learn/origin/afghanistan/emerald): Hydrothermal-sediment hosted Panjshir emerald; high Fe UV-Vis bands, low Li, three-phase inclusions in black shale context; distinction from Colombian.
- [Queensland Boulder Opal](https://gemmology.dev/learn/origin/australia/boulder-opal): Australian boulder opal with ironstone matrix backing - sources, patterns, and assessment criteria.
- [Brazilian Emerald](https://gemmology.dev/learn/origin/brazil/emerald): Brazilian emerald characteristics, comparison with Colombian material, and market position.
- [Burmese Sapphire](https://gemmology.dev/learn/origin/burma/sapphire): Mogok sapphire characteristics, inclusions, and market position relative to Kashmir and Ceylon.
- [Tsavorite Garnet](https://gemmology.dev/learn/origin/east-africa/tsavorite): East Africa's finest green garnet from Kenya and Tanzania - discovery, characteristics, and comparison with emerald.
- [Madagascar Ruby](https://gemmology.dev/learn/origin/madagascar/ruby): Ruby from Andilamena and other regions - characteristics, heat treatment, beryllium diffusion concerns.
- [Hunza Ruby — Pakistan](https://gemmology.dev/learn/origin/pakistan/ruby): Marble-hosted ruby from Hunza/Gilgit-Baltistan; low-Fe high-Cr chemistry analogous to Mogok; marble-suite inclusions; strong LWUV fluorescence.
- [Russian Alexandrite — Tokovaya District, Ural Mountains](https://gemmology.dev/learn/origin/russia/alexandrite): Tokovaya district alexandrite — 1830 discovery, named for Tsar Alexander II; benchmark colour change; mica-schist host; market position vs synthetic.
- [Thai Sapphire – Bo Phloi and Kanchanaburi Types](https://gemmology.dev/learn/origin/thailand/sapphire): Basaltic high-Fe blue sapphire from Bo Phloi and Kanchanaburi; strong 450/460/470 nm iron triplet, common heat treatment, basalt-suite inclusions.
- [Utah Red Beryl — Wah Wah Mountains](https://gemmology.dev/learn/origin/usa/utah-red-beryl): World's only commercial red beryl source — Mn³⁺-coloured beryl in Eocene topaz rhyolite, Wah Wah Mountains, Utah; properties, inclusions, market rarity.
- [Sri Lankan (Ceylon) Gems](https://gemmology.dev/learn/origin/ceylon): Sri Lankan sapphire, padparadscha, spinel, and other gems with characteristics, inclusions, and historical significance.
- [White Opal & Crystal Opal](https://gemmology.dev/learn/origin/australia/white-opal): Coober Pedy white opal and Australian crystal opal varieties - characteristics, quality grades, and market position.
- [Brazilian Aquamarine & Topaz](https://gemmology.dev/learn/origin/brazil/aquamarine): World-renowned Brazilian aquamarine including Santa Maria quality, and exclusive imperial topaz from Ouro Preto.
- [Burmese Spinel](https://gemmology.dev/learn/origin/burma/spinel): Mogok spinel - historic confusion with ruby, exceptional red and pink colours, and growing collector interest.
- [East African Ruby](https://gemmology.dev/learn/origin/east-africa/ruby): Ruby from Mozambique (Montepuez) and Kenya (John Saul Mine) - characteristics, inclusions, and market significance.
- [Madagascar Beryl](https://gemmology.dev/learn/origin/madagascar/beryl): Aquamarine, morganite, and limited emerald production from Madagascar - characteristics and market position.
- [Katlang Pink Topaz — Pakistan](https://gemmology.dev/learn/origin/pakistan/topaz): Chromium-coloured pink to champagne topaz from Katlang, Mardan district; Cr³⁺ colouring diagnostic, calcite-vein hosted, rare among topaz globally.
- [Ural Emerald — Malyshevsky, Russia](https://gemmology.dev/learn/origin/russia/emerald): Ural emerald from the Malyshevsky/Izumrudnye Kopi deposit; phlogopite mica inclusions diagnostic; Cr+V chromophores; mica-schist contact zone genesis.
- [Thai Blue Zircon – Heat-Treatment Hub](https://gemmology.dev/learn/origin/thailand/zircon): Thailand as the global centre for heat-treating Cambodian and Vietnamese zircon rough into blue zircon; origin, treatment process, and identification.
- [Colombian Emerald](https://gemmology.dev/learn/origin/colombia): Colombian emerald from Muzo, Chivor, and Coscuez with three-phase inclusions, characteristics, and market position.
- [Australian Sapphire](https://gemmology.dev/learn/origin/australia/sapphire): Australian sapphire characteristics including parti-sapphires, dark blues, and comparison with Asian sources.
- [Brazilian Tourmaline](https://gemmology.dev/learn/origin/brazil/tourmaline): Brazilian tourmaline varieties beyond Paraíba - rubellite, indicolite, chrome tourmaline, and other colours.
- [Burmese Jadeite](https://gemmology.dev/learn/origin/burma/jadeite): Imperial jade from Myanmar's Kachin State - the world's finest jadeite, characteristics, and the Asian market.
- [Mahenge Spinel](https://gemmology.dev/learn/origin/east-africa/spinel): Tanzania's exceptional neon pink to red spinel from the Mahenge region - discovery, characteristics, and market impact.
- [Rare Madagascar Gems](https://gemmology.dev/learn/origin/madagascar/rare-gems): Grandidierite, demantoid garnet, tourmaline, and other rare species from Madagascar's diverse geology.
- [Colombian Emerald Mines — Sub-Distinctions](https://gemmology.dev/learn/origin/colombia-mines): Mine-level diagnostics for Muzo (parisite + halite), Chivor (pyrite dominant), Coscuez, La Pita, and trapiche emerald; cross-reference to colombia.yaml.
- [Zambian Emerald](https://gemmology.dev/learn/origin/zambia): Zambian emerald characteristics, inclusions, comparison with Colombian, and market position.
- [Argyle Diamonds](https://gemmology.dev/learn/origin/australia/argyle-diamonds): The historic Argyle mine - world's primary pink diamond source, closure in 2020, and impact on the diamond market.
- [Paraiba-Type Tourmaline](https://gemmology.dev/learn/origin/east-africa/paraiba-type): Mozambican copper-bearing tourmaline with neon blue-green colours - discovery, characteristics, and the origin terminology debate.
- [Brazil — Imperial Topaz and Emerald Sub-distinctions](https://gemmology.dev/learn/origin/brazil-additional): Ouro Preto imperial topaz (Cr-coloured, strong LWUV fluorescence); Itabira vs Carnaíba emerald distinction (Cr vs V dominant, inclusion differences). Cross-reference brazil/ folder.
- [Cambodia — Pailin Sapphire and Battambang Ruby](https://gemmology.dev/learn/origin/cambodia): Cambodian gem deposits from Pailin (basaltic sapphire and ruby) and Battambang (marble-hosted ruby); Khmer Rouge era hiatus; distinction from Thai material.
- [Vietnam — Luc Yen Ruby and Cobalt-Blue Spinel](https://gemmology.dev/learn/origin/vietnam): Marble-hosted ruby and spinel from Luc Yen (Yen Bai) and Quy Chau; low-Fe high-Cr chemistry, cobalt-blue spinel, distinction from Burmese material.
- [Tajikistan – Kuh-i-Lal Spinel (Balas Ruby)](https://gemmology.dev/learn/origin/tajikistan): Kuh-i-Lal Gorno-Badakhshan red and pink spinel – historic "Balas ruby" of the Persian courts; Cr-coloured marble-hosted; trace element distinction from Mogok and Luc Yen.
- [India – Alexandrite, Diamond (Panna), and Garnet](https://gemmology.dev/learn/origin/india): Indian gem deposits – Andhra Pradesh alexandrite and chrysoberyl, Panna kimberlite diamond, Orissa garnet; geological context; Koh-i-Noor attribution qualified.
- [Iran – Nishapur (Neyshabur) Turquoise](https://gemmology.dev/learn/origin/iran): Persian turquoise from Neyshabur, Khorasan – the global colour standard; volcanic tuff host, spider-web matrix, Cu-Al phosphate, treatment assessment.
- [Mozambique — Montepuez Ruby and Paraíba Tourmaline](https://gemmology.dev/learn/origin/mozambique): Montepuez ruby (Cabo Delgado) — two-type amphibolite-hosted and alluvial; Mavuco Paraíba-type Cu-bearing tourmaline; LA-ICP-MS origin discrimination.
- [Zimbabwe — Sandawana Emerald and Marange Diamond](https://gemmology.dev/learn/origin/zimbabwe): Sandawana (Belingwe) emerald — vivid Cr-rich, tremolite inclusions, very small; Marange alluvial diamond; Murehwa chrysoberyl [CITATION NEEDED].
- [Ethiopia — Wollo Opal and Shakiso Emerald](https://gemmology.dev/learn/origin/ethiopia): Wollo (Welo) hydrophane opal — volcanic host, water-absorbing, distinct from Australian; Shakiso mica-schist emerald; Tigray sapphire [CITATION NEEDED].

### Market
- [Laboratory Reports](https://gemmology.dev/learn/market/lab-reports): Understanding gem laboratory reports from GIA, Gübelin, SSEF, GRS, and other major labs with terminology, grading, and certification.
- [Treatment Disclosure & Ethics](https://gemmology.dev/learn/market/disclosure): Treatment disclosure requirements, ethical standards, trade practices, and consumer protection in the gemstone industry.
- [Grading and Valuation](https://gemmology.dev/learn/market/grading-valuation): Colour grading (hue, tone, saturation), clarity assessment, cut quality, carat weight, and value factors for coloured gemstones.
- [Professional Practice](https://gemmology.dev/learn/market/professional-practice): Report writing, disclosure requirements, legal aspects, professional ethics, and laboratory certification for gemmologists.

### Care
- [Gem Care and Durability](https://gemmology.dev/learn/care/gem-care-durability): Gemstone stability, cleaning methods, setting recommendations, storage guidelines, and jewellery suitability for different gem species.

## Minerals

Each entry summarises crystal system, hardness range, RI range, SG range, origin classification, and a short reference description.

- [Actinolite](https://gemmology.dev/minerals/actinolite): monoclinic, H 5-6, RI 1.613-1.646, SG 3-3.44.
- [actinolite-prism](https://gemmology.dev/minerals/actinolite-prism)
- [Alexandrite](https://gemmology.dev/minerals/alexandrite): orthorhombic, H 8.5, RI 1.746-1.755, SG 3.71-3.75.
- [Almandine](https://gemmology.dev/minerals/almandine): cubic, H 7-7.5, RI 1.78-1.81, SG 4.05-4.3.
- [almandine-combination](https://gemmology.dev/minerals/almandine-combination)
- [almandine-dodecahedron](https://gemmology.dev/minerals/almandine-dodecahedron)
- [Amazonite](https://gemmology.dev/minerals/amazonite): triclinic, H 6-6.5, RI 1.522-1.53, SG 2.56-2.58.
- [Ambroid (Pressed Amber)](https://gemmology.dev/minerals/ambroid): amorphous, H 2-2.5, RI 1.53-1.545, SG 1.05-1.09, simulant.
- [Amethyst](https://gemmology.dev/minerals/amethyst): trigonal, H 7, RI 1.544-1.553, SG 2.65.
- [Ametrine](https://gemmology.dev/minerals/ametrine): trigonal, H 7, RI 1.544-1.553, SG 2.65.
- [Andalusite](https://gemmology.dev/minerals/andalusite): orthorhombic, H 7-7.5, RI 1.629-1.65, SG 3.13-3.17.
- [andalusite-chiastolite](https://gemmology.dev/minerals/andalusite-chiastolite)
- [Andesine](https://gemmology.dev/minerals/andesine): triclinic, H 6-6.5, RI 1.543-1.553, SG 2.65-2.69.
- [andesine-tabular](https://gemmology.dev/minerals/andesine-tabular)
- [Andradite](https://gemmology.dev/minerals/andradite): cubic, H 6.5-7, RI 1.855-1.895, SG 3.82-3.9.
- [andradite-dodecahedron](https://gemmology.dev/minerals/andradite-dodecahedron)
- [Apatite](https://gemmology.dev/minerals/apatite): hexagonal, H 5, RI 1.628-1.649, SG 3.16-3.22.
- [Aquamarine](https://gemmology.dev/minerals/aquamarine): hexagonal, H 7.5-8, RI 1.577-1.583, SG 2.67-2.78.
- [Aragonite](https://gemmology.dev/minerals/aragonite): orthorhombic, H 3.5-4, RI 1.53-1.685, SG 2.93-2.95.
- [Augite](https://gemmology.dev/minerals/augite): monoclinic, H 5.5-6, RI 1.68-1.735, SG 3.2-3.56.
- [augite-prism](https://gemmology.dev/minerals/augite-prism)
- [Azurite](https://gemmology.dev/minerals/azurite): monoclinic, H 3.5-4, RI 1.73-1.838, SG 3.77-3.89.
- [Barite](https://gemmology.dev/minerals/barite): orthorhombic, H 3, RI 1.636-1.648, SG 4.3-4.5.
- [Benitoite](https://gemmology.dev/minerals/benitoite): hexagonal, H 6-6.5, RI 1.757-1.804, SG 3.65-3.68.
- [Beryl](https://gemmology.dev/minerals/beryl): hexagonal, H 7.5-8, RI 1.577-1.583, SG 2.67-2.78.
- [beryl-prism](https://gemmology.dev/minerals/beryl-prism)
- [beryl-tabular](https://gemmology.dev/minerals/beryl-tabular)
- [Bone (Ivory Simulant)](https://gemmology.dev/minerals/bone): amorphous, H 2-3, RI 1.54-1.57, SG 1.7-2, simulant.
- [Bronzite](https://gemmology.dev/minerals/bronzite): orthorhombic, H 5-6, RI 1.653-1.71, SG 3.2-3.5.
- [bronzite-bronzite](https://gemmology.dev/minerals/bronzite-bronzite)
- [bronzite-cats-eye-enstatite](https://gemmology.dev/minerals/bronzite-cats-eye-enstatite)
- [Bytownite](https://gemmology.dev/minerals/bytownite): triclinic, H 6-6.5, RI 1.563-1.572, SG 2.72-2.74.
- [bytownite-tabular](https://gemmology.dev/minerals/bytownite-tabular)
- [Calcite](https://gemmology.dev/minerals/calcite): trigonal, H 3, RI 1.486-1.658, SG 2.71.
- [calcite-nailhead](https://gemmology.dev/minerals/calcite-nailhead)
- [calcite-rhomb](https://gemmology.dev/minerals/calcite-rhomb)
- [calcite-scalenohedron](https://gemmology.dev/minerals/calcite-scalenohedron)
- [calcite-stacked](https://gemmology.dev/minerals/calcite-stacked)
- [Cassiterite](https://gemmology.dev/minerals/cassiterite): tetragonal, H 6.5, RI 1.997-2.1, SG 6.85-7.04.
- [Celestine](https://gemmology.dev/minerals/celestine): orthorhombic, H 3-3.5, RI 1.619-1.632, SG 3.95-3.97.
- [Chalcedony](https://gemmology.dev/minerals/chalcedony): trigonal, H 6.5-7, RI 1.53-1.54, SG 2.58-2.64.
- [chalcedony-botryoidal](https://gemmology.dev/minerals/chalcedony-botryoidal)
- [chalcedony-massive](https://gemmology.dev/minerals/chalcedony-massive)
- [Chrome Diopside](https://gemmology.dev/minerals/chrome-diopside): monoclinic, H 5.5-6.5, RI 1.664-1.701, SG 3.22-3.38.
- [Chrysoberyl](https://gemmology.dev/minerals/chrysoberyl): orthorhombic, H 8.5, RI 1.746-1.755, SG 3.7-3.78.
- [chrysoberyl-cats-eye](https://gemmology.dev/minerals/chrysoberyl-cats-eye)
- [chrysoberyl-tabular](https://gemmology.dev/minerals/chrysoberyl-tabular)
- [chrysoberyl-trilling](https://gemmology.dev/minerals/chrysoberyl-trilling)
- [Chrysocolla](https://gemmology.dev/minerals/chrysocolla): amorphous, H 2.5-7, RI 1.46-1.57, SG 1.93-2.65.
- [Citrine](https://gemmology.dev/minerals/citrine): trigonal, H 7, RI 1.544-1.553, SG 2.65.
- [Colour-Change Garnet](https://gemmology.dev/minerals/colour-change-garnet): cubic, H 7-7.5, RI 1.74-1.76, SG 3.65-3.84.
- [colour-change-garnet-combination](https://gemmology.dev/minerals/colour-change-garnet-combination)
- [Copal (Amber Simulant)](https://gemmology.dev/minerals/copal): amorphous, H 1.5-2.5, RI 1.53-1.545, SG 1.04-1.1, simulant.
- [Coral](https://gemmology.dev/minerals/coral): amorphous, H 3-4, RI 1.486-1.658, SG 2.6-2.7.
- [Corundum](https://gemmology.dev/minerals/corundum): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.01.
- [corundum-barrel](https://gemmology.dev/minerals/corundum-barrel)
- [corundum-bipyramid](https://gemmology.dev/minerals/corundum-bipyramid)
- [Crocoite](https://gemmology.dev/minerals/crocoite): monoclinic, H 2.5-3, RI 2.31-2.66, SG 5.97-6.02.
- [Cubic Zirconia](https://gemmology.dev/minerals/cubic-zirconia): cubic, H 8-8.5, RI 2.15-2.18, SG 5.65-5.95, simulant.
- [cubic-zirconia-brilliant](https://gemmology.dev/minerals/cubic-zirconia-brilliant)
- [Cuprite](https://gemmology.dev/minerals/cuprite): cubic, H 3.5-4, RI 2.848, SG 6-6.14.
- [Demantoid](https://gemmology.dev/minerals/demantoid): cubic, H 6.5-7, RI 1.888-1.889, SG 3.82-3.85.
- [Diamond](https://gemmology.dev/minerals/diamond): cubic, H 10, RI 2.417, SG 3.52.
- [diamond-cube](https://gemmology.dev/minerals/diamond-cube)
- [diamond-macle](https://gemmology.dev/minerals/diamond-macle)
- [diamond-nested-phantom](https://gemmology.dev/minerals/diamond-nested-phantom)
- [diamond-octahedron](https://gemmology.dev/minerals/diamond-octahedron)
- [diamond-phantom](https://gemmology.dev/minerals/diamond-phantom)
- [Diopside](https://gemmology.dev/minerals/diopside): monoclinic, H 5.5-6.5, RI 1.675-1.701, SG 3.22-3.38.
- [Dravite](https://gemmology.dev/minerals/dravite): trigonal, H 7-7.5, RI 1.612-1.632, SG 2.98-3.1.
- [dravite-prism](https://gemmology.dev/minerals/dravite-prism)
- [Dyed Howlite (Turquoise Simulant)](https://gemmology.dev/minerals/dyed-howlite): monoclinic, H 3-3.5, RI 1.583-1.608, SG 2.53-2.59, simulant.
- [dyed-howlite-dyed](https://gemmology.dev/minerals/dyed-howlite-dyed)
- [Dyed Magnesite (Turquoise Simulant)](https://gemmology.dev/minerals/dyed-magnesite): trigonal, H 3.5-4.5, RI 1.509-1.7, SG 2.98-3.05, simulant.
- [dyed-magnesite-dyed](https://gemmology.dev/minerals/dyed-magnesite-dyed)
- [Elbaite](https://gemmology.dev/minerals/elbaite): trigonal, H 7-7.5, RI 1.615-1.638, SG 2.9-3.1.
- [elbaite-prism](https://gemmology.dev/minerals/elbaite-prism)
- [Emerald](https://gemmology.dev/minerals/emerald): hexagonal, H 7.5, RI 1.577-1.583, SG 2.72.
- [Enstatite](https://gemmology.dev/minerals/enstatite): orthorhombic, H 5-6, RI 1.656-1.669, SG 3.2-3.3.
- [enstatite-prism](https://gemmology.dev/minerals/enstatite-prism)
- [Epidote](https://gemmology.dev/minerals/epidote): monoclinic, H 6-7, RI 1.729-1.768, SG 3.35-3.5.
- [Fluorite](https://gemmology.dev/minerals/fluorite): cubic, H 4, RI 1.434, SG 3.18.
- [fluorite-cluster](https://gemmology.dev/minerals/fluorite-cluster)
- [fluorite-cube](https://gemmology.dev/minerals/fluorite-cube)
- [fluorite-cuboctahedron](https://gemmology.dev/minerals/fluorite-cuboctahedron)
- [fluorite-interpenetrating](https://gemmology.dev/minerals/fluorite-interpenetrating)
- [fluorite-octahedron](https://gemmology.dev/minerals/fluorite-octahedron)
- [fluorite-twin](https://gemmology.dev/minerals/fluorite-twin)
- [French Jet (Black Glass)](https://gemmology.dev/minerals/french-jet): amorphous, H 5-5.5, RI 1.48-1.7, SG 2.4-3.5, simulant.
- [Galena](https://gemmology.dev/minerals/galena): cubic, H 2.5, SG 7.4-7.6.
- [Garnet](https://gemmology.dev/minerals/garnet): cubic, H 6.5-7.5, RI 1.73-1.89, SG 3.5-4.3.
- [garnet-combination](https://gemmology.dev/minerals/garnet-combination)
- [garnet-dodecahedron](https://gemmology.dev/minerals/garnet-dodecahedron)
- [Garnet-Topped Doublet](https://gemmology.dev/minerals/garnet-topped-doublet): cubic, H 6.5-7, RI 1.73-1.78, SG 3-3.5, composite.
- [garnet-topped-doublet-doublet](https://gemmology.dev/minerals/garnet-topped-doublet-doublet)
- [garnet-trapezohedron](https://gemmology.dev/minerals/garnet-trapezohedron)
- [GGG (Gadolinium Gallium Garnet)](https://gemmology.dev/minerals/ggg): cubic, H 6.5, RI 2.02-2.03, SG 7.05, simulant.
- [ggg-faceted](https://gemmology.dev/minerals/ggg-faceted)
- [Glass (Paste)](https://gemmology.dev/minerals/glass-simulant): amorphous, H 5-6, RI 1.5-1.7, SG 2.3-4.5, simulant.
- [glass-simulant-faceted](https://gemmology.dev/minerals/glass-simulant-faceted)
- [Goshenite](https://gemmology.dev/minerals/goshenite): hexagonal, H 7.5-8, RI 1.564-1.6, SG 2.68-2.8.
- [Grossular](https://gemmology.dev/minerals/grossular): cubic, H 6.5-7, RI 1.73-1.76, SG 3.57-3.73.
- [grossular-trapezohedron](https://gemmology.dev/minerals/grossular-trapezohedron)
- [Gypsum](https://gemmology.dev/minerals/gypsum): monoclinic, H 2, RI 1.52-1.53, SG 2.31-2.33.
- [gypsum-swallowtail](https://gemmology.dev/minerals/gypsum-swallowtail)
- [gypsum-tabular](https://gemmology.dev/minerals/gypsum-tabular)
- [Halite](https://gemmology.dev/minerals/halite): cubic, H 2.5, RI 1.544, SG 2.17.
- [Hauyne](https://gemmology.dev/minerals/hauyne): cubic, H 5.5-6, RI 1.494-1.509, SG 2.4-2.5.
- [Heliodor](https://gemmology.dev/minerals/heliodor): hexagonal, H 7.5-8, RI 1.577-1.583, SG 2.67-2.78.
- [Hematite](https://gemmology.dev/minerals/hematite): trigonal, H 5.5-6.5, SG 5-5.3.
- [hematite-kidney-ore](https://gemmology.dev/minerals/hematite-kidney-ore)
- [hematite-specularite](https://gemmology.dev/minerals/hematite-specularite)
- [Hessonite](https://gemmology.dev/minerals/hessonite): cubic, H 6.5-7, RI 1.742-1.748, SG 3.57-3.67.
- [hessonite-trapezohedron](https://gemmology.dev/minerals/hessonite-trapezohedron)
- [Hiddenite](https://gemmology.dev/minerals/hiddenite): monoclinic, H 6.5-7, RI 1.66-1.676, SG 3.15-3.21.
- [Hydrogrossular](https://gemmology.dev/minerals/hydrogrossular): cubic, H 6.5-7, RI 1.71-1.73, SG 3.36-3.55.
- [Jadeite](https://gemmology.dev/minerals/jadeite): monoclinic, H 6.5-7, RI 1.654-1.688, SG 3.25-3.36.
- [jadeite-crystal](https://gemmology.dev/minerals/jadeite-crystal)
- [jadeite-massive](https://gemmology.dev/minerals/jadeite-massive)
- [Jet](https://gemmology.dev/minerals/jet): amorphous, H 2.5-4, RI 1.64-1.68, SG 1.19-1.35.
- [Kornerupine](https://gemmology.dev/minerals/kornerupine): orthorhombic, H 6.5-7, RI 1.661-1.683, SG 3.27-3.45.
- [kornerupine-cats-eye](https://gemmology.dev/minerals/kornerupine-cats-eye)
- [Kunzite](https://gemmology.dev/minerals/kunzite): monoclinic, H 6.5, RI 1.66-1.676, SG 3.15-3.21.
- [Kyanite](https://gemmology.dev/minerals/kyanite): triclinic, RI 1.716-1.731, SG 3.53-3.68.
- [Labradorite](https://gemmology.dev/minerals/labradorite): triclinic, H 6-6.5, RI 1.559-1.568, SG 2.69-2.72.
- [Lazurite](https://gemmology.dev/minerals/lazurite): cubic, H 5-5.5, RI 1.5, SG 2.38-2.45.
- [lazurite-crystal](https://gemmology.dev/minerals/lazurite-crystal)
- [lazurite-massive](https://gemmology.dev/minerals/lazurite-massive)
- [LuAG (Lutetium Aluminium Garnet)](https://gemmology.dev/minerals/luag): cubic, H 8.5, RI 1.84, SG 6.73, simulant.
- [luag-faceted](https://gemmology.dev/minerals/luag-faceted)
- [Magnetite](https://gemmology.dev/minerals/magnetite): cubic, H 5.5-6.5, SG 5.17-5.18.
- [Malachite](https://gemmology.dev/minerals/malachite): monoclinic, H 3.5-4, RI 1.655-1.909, SG 3.6-4.
- [malachite-crystal](https://gemmology.dev/minerals/malachite-crystal)
- [malachite-massive](https://gemmology.dev/minerals/malachite-massive)
- [Maw-Sit-Sit](https://gemmology.dev/minerals/maw-sit-sit): monoclinic, H 6-7, RI 1.52-1.68, SG 3-3.4.
- [Maxixe-type Beryl](https://gemmology.dev/minerals/maxixe-beryl): hexagonal, H 7.5-8, RI 1.563-1.578, SG 2.68-2.76.
- [Moissanite](https://gemmology.dev/minerals/moissanite): hexagonal, H 9.25-9.5, RI 2.648-2.691, SG 3.21-3.22, simulant.
- [moissanite-faceted](https://gemmology.dev/minerals/moissanite-faceted)
- [Moldavite](https://gemmology.dev/minerals/moldavite): amorphous, H 5-5.5, RI 1.48-1.51, SG 2.32-2.38.
- [moldavite-natural](https://gemmology.dev/minerals/moldavite-natural)
- [Moonstone](https://gemmology.dev/minerals/moonstone): monoclinic, H 6-6.5, RI 1.518-1.526, SG 2.56-2.59.
- [Morganite](https://gemmology.dev/minerals/morganite): hexagonal, H 7.5-8, RI 1.577-1.583, SG 2.67-2.78.
- [Musgravite](https://gemmology.dev/minerals/musgravite): hexagonal, H 8-8.5, RI 1.719-1.736, SG 3.61-3.68.
- [Nephrite](https://gemmology.dev/minerals/nephrite): monoclinic, H 6-6.5, RI 1.6-1.627, SG 2.9-3.1.
- [nephrite-massive](https://gemmology.dev/minerals/nephrite-massive)
- [Obsidian](https://gemmology.dev/minerals/obsidian): amorphous, H 5-5.5, RI 1.48-1.51, SG 2.33-2.5.
- [obsidian-snowflake](https://gemmology.dev/minerals/obsidian-snowflake)
- [Opal](https://gemmology.dev/minerals/opal): amorphous, H 5.5-6.5, RI 1.37-1.47, SG 1.98-2.25.
- [Opal Doublet](https://gemmology.dev/minerals/opal-doublet): amorphous, H 5.5-6.5, RI 1.44-1.46, SG 1.9-2.1, composite.
- [opal-doublet-cabochon](https://gemmology.dev/minerals/opal-doublet-cabochon)
- [Opal Triplet](https://gemmology.dev/minerals/opal-triplet): amorphous, H 5.5-7, RI 1.44-1.55, SG 1.9-2.1, composite.
- [opal-triplet-cabochon](https://gemmology.dev/minerals/opal-triplet-cabochon)
- [Orpiment](https://gemmology.dev/minerals/orpiment): monoclinic, H 1.5-2, RI 2.4-3, SG 3.46-3.49.
- [Orthoclase](https://gemmology.dev/minerals/orthoclase): monoclinic, H 6-6.5, RI 1.518-1.526, SG 2.55-2.63.
- [orthoclase-baveno](https://gemmology.dev/minerals/orthoclase-baveno)
- [orthoclase-carlsbad](https://gemmology.dev/minerals/orthoclase-carlsbad)
- [orthoclase-prismatic](https://gemmology.dev/minerals/orthoclase-prismatic)
- [Padparadscha Sapphire](https://gemmology.dev/minerals/padparadscha): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.02.
- [padparadscha-bipyramid](https://gemmology.dev/minerals/padparadscha-bipyramid)
- [Pearl](https://gemmology.dev/minerals/pearl): orthorhombic, H 2.5-4.5, RI 1.52-1.69, SG 2.6-2.85.
- [pearl-aragonite](https://gemmology.dev/minerals/pearl-aragonite)
- [pearl-nacre](https://gemmology.dev/minerals/pearl-nacre)
- [Peridot](https://gemmology.dev/minerals/peridot): orthorhombic, H 6.5, RI 1.654-1.69, SG 3.27-3.37.
- [Pink Sapphire](https://gemmology.dev/minerals/pink-sapphire): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.02.
- [pink-sapphire-bipyramid](https://gemmology.dev/minerals/pink-sapphire-bipyramid)
- [Plagioclase (Albite Twin)](https://gemmology.dev/minerals/plagioclase-albite): triclinic, H 6-6.5, RI 1.525-1.59, SG 2.62-2.76.
- [Pyrite](https://gemmology.dev/minerals/pyrite): cubic, H 6.5, SG 4.95-5.1.
- [pyrite-cluster](https://gemmology.dev/minerals/pyrite-cluster)
- [pyrite-cube](https://gemmology.dev/minerals/pyrite-cube)
- [pyrite-iron-cross](https://gemmology.dev/minerals/pyrite-iron-cross)
- [pyrite-pyritohedron](https://gemmology.dev/minerals/pyrite-pyritohedron)
- [Pyrope](https://gemmology.dev/minerals/pyrope): cubic, H 7-7.5, RI 1.74-1.76, SG 3.51-3.65.
- [pyrope-dodecahedron](https://gemmology.dev/minerals/pyrope-dodecahedron)
- [Quartz](https://gemmology.dev/minerals/quartz): trigonal, H 7, RI 1.544-1.553, SG 2.65.
- [quartz-amethyst-geode](https://gemmology.dev/minerals/quartz-amethyst-geode)
- [quartz-brazil-twin](https://gemmology.dev/minerals/quartz-brazil-twin)
- [quartz-cluster](https://gemmology.dev/minerals/quartz-cluster)
- [quartz-dauphine-twin](https://gemmology.dev/minerals/quartz-dauphine-twin)
- [quartz-faden](https://gemmology.dev/minerals/quartz-faden)
- [quartz-japan-twin](https://gemmology.dev/minerals/quartz-japan-twin)
- [quartz-phantom](https://gemmology.dev/minerals/quartz-phantom)
- [quartz-prism](https://gemmology.dev/minerals/quartz-prism)
- [quartz-scepter](https://gemmology.dev/minerals/quartz-scepter)
- [quartz-short](https://gemmology.dev/minerals/quartz-short)
- [Realgar](https://gemmology.dev/minerals/realgar): monoclinic, H 1.5-2, RI 2.538-2.684, SG 3.52-3.56.
- [Reconstructed Turquoise](https://gemmology.dev/minerals/reconstructed-turquoise): triclinic, H 4-5.5, RI 1.61-1.65, SG 2.3-2.6, simulant.
- [Red Beryl](https://gemmology.dev/minerals/red-beryl): hexagonal, H 7.5-8, RI 1.564-1.574, SG 2.66-2.7.
- [Rhodochrosite](https://gemmology.dev/minerals/rhodochrosite): trigonal, H 3.5-4, RI 1.597-1.817, SG 3.45-3.7.
- [rhodochrosite-banded](https://gemmology.dev/minerals/rhodochrosite-banded)
- [Rhodolite](https://gemmology.dev/minerals/rhodolite): cubic, H 7-7.5, RI 1.76, SG 3.84.
- [Rhodonite](https://gemmology.dev/minerals/rhodonite): triclinic, H 5.5-6.5, RI 1.711-1.751, SG 3.4-3.74.
- [Rose Quartz](https://gemmology.dev/minerals/rose-quartz): trigonal, H 7, RI 1.544-1.553, SG 2.65.
- [rose-quartz-massive](https://gemmology.dev/minerals/rose-quartz-massive)
- [rose-quartz-star](https://gemmology.dev/minerals/rose-quartz-star)
- [Ruby](https://gemmology.dev/minerals/ruby): trigonal, H 9, RI 1.762-1.77, SG 4.
- [ruby-star](https://gemmology.dev/minerals/ruby-star)
- [Rutile](https://gemmology.dev/minerals/rutile): tetragonal, H 6, RI 2.616-2.903, SG 4.23-4.26.
- [Sanidine](https://gemmology.dev/minerals/sanidine): monoclinic, H 6, RI 1.518-1.527, SG 2.52-2.62.
- [sanidine-tabular](https://gemmology.dev/minerals/sanidine-tabular)
- [Sapphire](https://gemmology.dev/minerals/sapphire): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.01.
- [sapphire-star](https://gemmology.dev/minerals/sapphire-star)
- [Scapolite](https://gemmology.dev/minerals/scapolite): tetragonal, H 5.5-6, RI 1.536-1.6, SG 2.5-2.78.
- [scapolite-cats-eye](https://gemmology.dev/minerals/scapolite-cats-eye)
- [scapolite-prismatic](https://gemmology.dev/minerals/scapolite-prismatic)
- [Scheelite](https://gemmology.dev/minerals/scheelite): tetragonal, H 4.5-5, RI 1.918-1.937, SG 5.9-6.1.
- [Schorl](https://gemmology.dev/minerals/schorl): trigonal, H 7-7.5, RI 1.635-1.655, SG 3.1-3.25.
- [schorl-prism](https://gemmology.dev/minerals/schorl-prism)
- [Serpentine](https://gemmology.dev/minerals/serpentine): monoclinic, H 2.5-5, RI 1.55-1.57, SG 2.44-2.62.
- [serpentine-bowenite](https://gemmology.dev/minerals/serpentine-bowenite)
- [serpentine-williamsite](https://gemmology.dev/minerals/serpentine-williamsite)
- [Sinhalite](https://gemmology.dev/minerals/sinhalite): orthorhombic, H 6.5, RI 1.668-1.707, SG 3.46-3.5.
- [Slocum Stone](https://gemmology.dev/minerals/slocum-stone): amorphous, H 5-5.5, RI 1.48-1.52, SG 2.4-2.5, simulant.
- [Smoky Quartz](https://gemmology.dev/minerals/smoky-quartz): trigonal, H 7, RI 1.544-1.553, SG 2.65.
- [smoky-quartz-morion](https://gemmology.dev/minerals/smoky-quartz-morion)
- [smoky-quartz-prism](https://gemmology.dev/minerals/smoky-quartz-prism)
- [Sodalite](https://gemmology.dev/minerals/sodalite): cubic, H 5.5-6, RI 1.483-1.487, SG 2.27-2.33.
- [sodalite-crystal](https://gemmology.dev/minerals/sodalite-crystal)
- [sodalite-massive](https://gemmology.dev/minerals/sodalite-massive)
- [Soudé Emerald](https://gemmology.dev/minerals/soude-emerald): hexagonal, H 7.5, RI 1.57-1.58, SG 2.68-2.72, composite.
- [soude-emerald-doublet](https://gemmology.dev/minerals/soude-emerald-doublet)
- [Spessartine](https://gemmology.dev/minerals/spessartine): cubic, H 7-7.5, RI 1.79-1.81, SG 4.12-4.2.
- [Sphene (Titanite)](https://gemmology.dev/minerals/sphene): monoclinic, H 5-5.5, RI 1.9-2.034, SG 3.52-3.54.
- [Spinel](https://gemmology.dev/minerals/spinel): cubic, H 8, RI 1.712-1.72, SG 3.58-3.61.
- [spinel-macle](https://gemmology.dev/minerals/spinel-macle)
- [spinel-octahedron](https://gemmology.dev/minerals/spinel-octahedron)
- [Spodumene](https://gemmology.dev/minerals/spodumene): monoclinic, H 6.5-7, RI 1.66-1.676, SG 3.15-3.2.
- [spodumene-prism](https://gemmology.dev/minerals/spodumene-prism)
- [Star Diopside](https://gemmology.dev/minerals/star-diopside): monoclinic, H 5.5-6, RI 1.664-1.701, SG 3.27-3.38.
- [star-diopside-star-cabochon](https://gemmology.dev/minerals/star-diopside-star-cabochon)
- [Staurolite](https://gemmology.dev/minerals/staurolite): orthorhombic, H 7-7.5, RI 1.736-1.762, SG 3.65-3.79.
- [staurolite-cross-60](https://gemmology.dev/minerals/staurolite-cross-60)
- [staurolite-cross-90](https://gemmology.dev/minerals/staurolite-cross-90)
- [Strontium Titanate](https://gemmology.dev/minerals/strontium-titanate): cubic, H 5.5, RI 2.409, SG 5.13, simulant.
- [strontium-titanate-faceted](https://gemmology.dev/minerals/strontium-titanate-faceted)
- [Sunstone](https://gemmology.dev/minerals/sunstone): triclinic, H 6-6.5, RI 1.537-1.547, SG 2.62-2.67.
- [Synthetic Alexandrite](https://gemmology.dev/minerals/synthetic-alexandrite-czochralski): orthorhombic, H 8.5, RI 1.744-1.755, SG 3.71, synthetic.
- [synthetic-alexandrite-czochralski-boule](https://gemmology.dev/minerals/synthetic-alexandrite-czochralski-boule)
- [Flux-Grown Alexandrite](https://gemmology.dev/minerals/synthetic-alexandrite-flux): orthorhombic, RI 1.746-1.755, SG 3.7-3.73, synthetic.
- [synthetic-alexandrite-flux-crystal](https://gemmology.dev/minerals/synthetic-alexandrite-flux-crystal)
- [Hydrothermal Alexandrite](https://gemmology.dev/minerals/synthetic-alexandrite-hydrothermal): orthorhombic, RI 1.746-1.755, SG 3.7-3.73, synthetic.
- [synthetic-alexandrite-hydrothermal-crystal](https://gemmology.dev/minerals/synthetic-alexandrite-hydrothermal-crystal)
- [Synthetic Coral](https://gemmology.dev/minerals/synthetic-coral): trigonal, H 3-3.5, RI 1.48-1.65, SG 2.4-2.6, simulant.
- [synthetic-coral-cabochon](https://gemmology.dev/minerals/synthetic-coral-cabochon)
- [CVD Diamond](https://gemmology.dev/minerals/synthetic-diamond-cvd): cubic, H 10, RI 2.417, SG 3.52, synthetic.
- [synthetic-diamond-cvd-plate](https://gemmology.dev/minerals/synthetic-diamond-cvd-plate)
- [HPHT Diamond](https://gemmology.dev/minerals/synthetic-diamond-hpht): cubic, H 10, RI 2.417, SG 3.52, synthetic.
- [synthetic-diamond-hpht-cuboctahedron](https://gemmology.dev/minerals/synthetic-diamond-hpht-cuboctahedron)
- [Flux-Grown Emerald](https://gemmology.dev/minerals/synthetic-emerald-flux): hexagonal, H 7.5, RI 1.56-1.563, SG 2.65-2.66, synthetic.
- [synthetic-emerald-flux-crystal](https://gemmology.dev/minerals/synthetic-emerald-flux-crystal)
- [Hydrothermal Emerald](https://gemmology.dev/minerals/synthetic-emerald-hydrothermal): hexagonal, H 7.5, RI 1.568-1.573, SG 2.68-2.7, synthetic.
- [synthetic-emerald-hydrothermal-crystal](https://gemmology.dev/minerals/synthetic-emerald-hydrothermal-crystal)
- [Lechleitner Emerald (Overgrowth)](https://gemmology.dev/minerals/synthetic-emerald-lechleitner): hexagonal, H 7.5-8, RI 1.565-1.602, SG 2.67-2.72, synthetic.
- [synthetic-emerald-lechleitner-crystal](https://gemmology.dev/minerals/synthetic-emerald-lechleitner-crystal)
- [Gilson Lapis Lazuli](https://gemmology.dev/minerals/synthetic-lapis-gilson): cubic, H 5-5.5, RI 1.5-1.52, SG 2.3-2.4, simulant.
- [synthetic-lapis-gilson-cabochon](https://gemmology.dev/minerals/synthetic-lapis-gilson-cabochon)
- [Gilson Opal](https://gemmology.dev/minerals/synthetic-opal-gilson): amorphous, H 5.5-6, RI 1.44-1.46, SG 2.05-2.15, synthetic.
- [synthetic-opal-gilson-cabochon](https://gemmology.dev/minerals/synthetic-opal-gilson-cabochon)
- [Lab-Grown Paraíba Tourmaline](https://gemmology.dev/minerals/synthetic-paraiba): trigonal, H 7-7.5, RI 1.62-1.64, SG 3.05-3.1, synthetic.
- [synthetic-paraiba-crystal](https://gemmology.dev/minerals/synthetic-paraiba-crystal)
- [Hydrothermal Quartz](https://gemmology.dev/minerals/synthetic-quartz-hydrothermal): trigonal, H 7, RI 1.544-1.553, SG 2.65, synthetic.
- [synthetic-quartz-hydrothermal-crystal](https://gemmology.dev/minerals/synthetic-quartz-hydrothermal-crystal)
- [Flux-Grown Ruby](https://gemmology.dev/minerals/synthetic-ruby-flux): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.01, synthetic.
- [synthetic-ruby-flux-crystal](https://gemmology.dev/minerals/synthetic-ruby-flux-crystal)
- [Hydrothermal Ruby](https://gemmology.dev/minerals/synthetic-ruby-hydrothermal): trigonal, RI 1.762-1.77, SG 3.99-4.01, synthetic.
- [synthetic-ruby-hydrothermal-crystal](https://gemmology.dev/minerals/synthetic-ruby-hydrothermal-crystal)
- [Kashan Flux Ruby](https://gemmology.dev/minerals/synthetic-ruby-kashan-flux): trigonal, RI 1.762-1.77, SG 3.99-4.01, synthetic.
- [synthetic-ruby-kashan-flux-crystal](https://gemmology.dev/minerals/synthetic-ruby-kashan-flux-crystal)
- [Synthetic Ruby (Verneuil)](https://gemmology.dev/minerals/synthetic-ruby-verneuil): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.01, synthetic.
- [synthetic-ruby-verneuil-boule](https://gemmology.dev/minerals/synthetic-ruby-verneuil-boule)
- [Synthetic Rutile](https://gemmology.dev/minerals/synthetic-rutile): tetragonal, H 6-6.5, RI 2.616-2.903, SG 4.25, simulant.
- [synthetic-rutile-faceted](https://gemmology.dev/minerals/synthetic-rutile-faceted)
- [Czochralski Sapphire](https://gemmology.dev/minerals/synthetic-sapphire-czochralski): trigonal, RI 1.762-1.77, SG 3.99-4.01, synthetic.
- [synthetic-sapphire-czochralski-crystal](https://gemmology.dev/minerals/synthetic-sapphire-czochralski-crystal)
- [Flux-Grown Sapphire](https://gemmology.dev/minerals/synthetic-sapphire-flux): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.01, synthetic.
- [synthetic-sapphire-flux-crystal](https://gemmology.dev/minerals/synthetic-sapphire-flux-crystal)
- [Synthetic Sapphire (Verneuil)](https://gemmology.dev/minerals/synthetic-sapphire-verneuil): trigonal, H 9, RI 1.762-1.77, SG 3.99-4.01, synthetic.
- [synthetic-sapphire-verneuil-boule](https://gemmology.dev/minerals/synthetic-sapphire-verneuil-boule)
- [Synthetic Spinel (Verneuil)](https://gemmology.dev/minerals/synthetic-spinel-verneuil): cubic, H 8, RI 1.727, SG 3.64, synthetic.
- [synthetic-spinel-verneuil-boule](https://gemmology.dev/minerals/synthetic-spinel-verneuil-boule)
- [Gilson Turquoise](https://gemmology.dev/minerals/synthetic-turquoise-gilson): triclinic, H 5-6, RI 1.6-1.61, SG 2.4-2.5, simulant.
- [synthetic-turquoise-gilson-cabochon](https://gemmology.dev/minerals/synthetic-turquoise-gilson-cabochon)
- [Taaffeite](https://gemmology.dev/minerals/taaffeite): hexagonal, H 8-8.5, RI 1.717-1.73, SG 3.6-3.62.
- [Tanzanite](https://gemmology.dev/minerals/tanzanite): orthorhombic, H 6.5, RI 1.691-1.7, SG 3.1-3.38.
- [Topaz](https://gemmology.dev/minerals/topaz): orthorhombic, H 8, RI 1.619-1.627, SG 3.5-3.57.
- [topaz-prism](https://gemmology.dev/minerals/topaz-prism)
- [topaz-tabular](https://gemmology.dev/minerals/topaz-tabular)
- [Tourmaline](https://gemmology.dev/minerals/tourmaline): trigonal, H 7-7.5, RI 1.62-1.64, SG 3.01-3.11.
- [tourmaline-prism](https://gemmology.dev/minerals/tourmaline-prism)
- [tourmaline-watermelon](https://gemmology.dev/minerals/tourmaline-watermelon)
- [Tremolite](https://gemmology.dev/minerals/tremolite): monoclinic, H 5-6, RI 1.599-1.628, SG 2.9-3.1.
- [tremolite-prism](https://gemmology.dev/minerals/tremolite-prism)
- [Tsavorite](https://gemmology.dev/minerals/tsavorite): cubic, H 7-7.5, RI 1.74, SG 3.61.
- [Turquoise](https://gemmology.dev/minerals/turquoise): triclinic, H 5-6, RI 1.61-1.65, SG 2.6-2.85.
- [turquoise-crystal](https://gemmology.dev/minerals/turquoise-crystal)
- [turquoise-massive](https://gemmology.dev/minerals/turquoise-massive)
- [Uvarovite](https://gemmology.dev/minerals/uvarovite): cubic, H 6.5-7, RI 1.87, SG 3.77.
- [uvarovite-druse](https://gemmology.dev/minerals/uvarovite-druse)
- [Vesuvianite](https://gemmology.dev/minerals/vesuvianite): tetragonal, H 6.5, RI 1.7-1.752, SG 3.32-3.42.
- [Vulcanite (Jet Simulant)](https://gemmology.dev/minerals/vulcanite): amorphous, H 2.5-3.5, RI 1.66, SG 1.1-1.2, simulant.
- [Wulfenite](https://gemmology.dev/minerals/wulfenite): tetragonal, H 2.5-3, RI 2.28-2.4, SG 6.7-7.
- [YAG (Yttrium Aluminium Garnet)](https://gemmology.dev/minerals/yag): cubic, H 8, RI 1.833, SG 4.55, simulant.
- [yag-faceted](https://gemmology.dev/minerals/yag-faceted)
- [Zircon](https://gemmology.dev/minerals/zircon): tetragonal, H 7.5, RI 1.925-1.984, SG 4.6-4.7.

## Licensing (training use)

- Code (TypeScript, Python packages, build pipeline) is licensed under MIT.
- Educational content (`/learn/` articles and the upstream `gemmology-knowledge` curriculum) is licensed under CC BY-SA 4.0.
- AI training and AI-search use of this content is permitted under those licences, subject to attribution to gemmology.dev and ShareAlike for derivative works of the educational content.
- The mineral reference data is compiled from peer-reviewed gemmological sources; numerical ranges are verified across multiple sources before inclusion. See [About](https://gemmology.dev/about/) for editorial standards.

## Source
- https://github.com/gemmology-dev
- Corrections via GitHub issues at https://github.com/gemmology-dev/gemmology.dev/issues