Amphibole Group (Nephrite)
Amphibole group gems, primarily nephrite jade, with properties, comparison to jadeite, sources, and identification.
Introduction
Nephrite is one of the two minerals traditionally called jade, belonging to the amphibole
group as a calcium magnesium iron silicate (Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂) with a monoclinic
crystal system, though gem material occurs as a cryptocrystalline fibrous aggregate rather
than single crystals. Its interlocking fibre structure makes it the toughest natural
material known, tougher than steel, a quality that drove its use for prehistoric tools
and weapons over 8,000 years. [1] Diagnostic properties: spot RI of
1.606–1.632, SG 2.90–3.02, and hardness 6–6.5 Mohs. These values immediately separate
nephrite from the more valuable jadeite (RI 1.654–1.667, SG 3.30–3.38), serpentine
simulants (SG 2.5–2.6), and hydrogrossular garnet (SG 3.4+). Colour ranges from white
("mutton fat" tremolite-rich nephrite) through spinach-green (iron-rich actinolite) to
black. Fine white nephrite from Hetian, Xinjiang, China (known as Hetian jade or
seed jade when river-worn) is the most culturally prized jade in China and commands
premiums that rival fine jadeite in the Chinese market.
Nephrite
Nephrite is a variety of actinolite-tremolite, prized for its toughness
and carving qualities.
Properties
| Property | Value |
|---|---|
| Composition | Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂ |
| Crystal system | Monoclinic (but cryptocrystalline aggregate) |
| Hardness | 6–6.5 Mohs |
| Specific gravity | 2.90–3.02 |
| Refractive index | 1.606–1.632 (spot) |
| Character | Aggregate (fibrous) |
| Toughness | Exceptional |
Colour Varieties
Nephrite occurs in various colours:
- Green: Iron content; most common
- White ("mutton fat"): Pure tremolite; prized in China
- Brown: Higher iron; weathered surfaces
- Black: High iron content
- Yellow: Iron oxidation
Tremolite vs Actinolite
Nephrite composition varies:
- Tremolite: Mg-rich; tends to white/cream colours
- Actinolite: Fe-substituted; tends to green colours
- Most nephrite is intermediate
- Colour correlates with composition
Exceptional Toughness
Nephrite vs Jadeite
Nephrite
- Amphibole (actinolite-tremolite)
- SG 2.90–3.02 (lower) {cite:read-3rd}
- RI 1.606–1.632 (lower)
- Greasy to waxy lustre
- More subdued greens
- Generally more affordable
- Traditional Chinese "yu"
Jadeite
- Pyroxene (sodium aluminium)
- SG 3.30–3.38 (higher)
- RI 1.654–1.667 (higher)
- Vitreous lustre
- Vivid "Imperial" green possible
- Higher value for fine material
- "Fei-cui" in Chinese
Major Sources
| Origin | Characteristics | Cultural Significance |
|---|---|---|
| China (Hetian/Khotan) | White 'mutton fat' jade | Most prized in Chinese culture |
| New Zealand | Green; Māori 'pounamu' | Sacred to Māori culture |
| Canada (BC) | Green; large deposits | Major modern source |
| Russia (Siberia) | Dark green to black | Significant deposits |
| Australia | Variable quality | Commercial production |
| USA (Wyoming) | Green | Historic and current |
Chinese White Jade
Cultural Significance
Jade holds profound cultural meaning:
Chinese Culture
- Symbol of virtue, beauty, and immortality
- Used for imperial seals and ceremonial objects
- Believed to protect and purify
- Jade burial suits for nobility
- Continuous 8,000-year tradition
Māori Culture
- Pounamu (greenstone) is taonga (treasure)
- Traditional weapons (mere) and ornaments (hei-tiki)
- Passed down through generations
- Spiritual significance
- Protected under New Zealand law [CITATION NEEDED]
Identification
Distinguishing nephrite from simulants:
Key Tests
- Specific gravity: 2.90–3.02 (flotation test) [1]
- Spot RI: ~1.61 (distinguishes from jadeite)
- Structure: Fibrous under magnification
- Feel: Greasy/waxy to touch
- Toughness: Exceptional (doesn't chip easily)
Common Simulants
| Material | Distinction |
|---|---|
| Serpentine | Lower SG (2.5–2.6); softer (H 2.5–5) |
| Chrysoprase | Different RI (1.53–1.54); SG 2.6 |
| Aventurine quartz | Different RI (1.54); sparkle from inclusions |
| Hydrogrossular garnet | Higher SG (3.4+); SR |
| Glass | Gas bubbles; different feel |
Care and Durability
Despite toughness, nephrite requires some care:
- Avoid harsh chemicals
- Clean with warm soapy water
- Ultrasonic generally safe (solid pieces)
- Can be oiled to enhance lustre
- Surface can be scratched (H 6–6.5)
- Excellent for carvings and daily-wear jewellery
References
- ↑ 1. Read, P. (2008). Gemmology (3rd ed.). Butterworth-Heinemann. ISBN: 978-0-7506-6449-3. DOI: 10.4324/9780080507224.