hexagonal Cyclosilicates
Goshenite
Be3Al2Si6O18
Crystal Structure
#! Species: Goshenite (Beryl, colourless variety)
#! System: Hexagonal (6/mmm)
#! Habit: Prismatic hexagonal crystals; colourless
hexagonal[6/mmm]:{10-10}@1.0 + {0001}@0.6
hexagonal
6/mmm
{10-10} {0001}
Quick Facts
Hardness
7.5
Specific Gravity
2.68
Refractive Index
1.564
Optical Character
Uniaxial -
Physical Properties
Crystal Systemhexagonal
Hardness (Mohs)7.5
Specific Gravity2.68
CleavageImperfect basal
FractureConchoidal
LustreVitreous
Optical Properties
Refractive Index1.564
Birefringence0.005-0.008
Optical CharacterUniaxial -
Dispersion0.014
PleochroismNone
Colours
Colourless (pure; no chromophore)
Localities
Goshen, Massachusetts, USA (type locality)Brazil (Minas Gerais; major source)Pakistan (Gilgit-Baltistan)Nigeria, NamibiaChina
Common Inclusions
Two-phase fluid inclusionsGrowth tubes parallel to c-axisOccasional negative crystals
Known Treatments
Not routinely treated; occasionally irradiated to produce aquamarine or Maxixe-type colour
Crystal Forms
prismpinacoid
Diagnostic Features
Colourless beryl; uniaxial negative; RI 1.564-1.600; SG 2.68-2.80; hardness 7.5-8; separates from colourless topaz (biaxial +; SG 3.50), colourless sapphire (uniaxial -; much higher SG 4.00), and phenakite (uniaxial +; lower SG 2.95)
Notes
Colourless variety of beryl (Be3Al2Si6O18). Chemistry per VERIFIED.md conflict resolution F-01: correct cyclosilicate formula Be3Al2Si6O18 (NOT Be3Al2(SiO3)6). Beryl formula confirmed by Read 7th ed. (DOI 10.4324/9780080507224) and Turner & Groat (ch. 5) (DOI 10.3749/9780921294696.ch05) [VERIFIED]. Goshenite is the pure beryl end-member, colourless due to absence of chromophores. Named after Goshen, Massachusetts. May contain colourless beryl seed cores in synthetic emerald Lechleitner overgrowth production.
Related Minerals
Other minerals in the hexagonal system
