16.11: Spodumene
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|---|---|
| Chemical composition | LiAl(SiO3)2 |
| Crystal system | Monoclinic |
| Habit | Prismatic, tabular |
| Cleavage | Perfect, prismatic |
| Fracture | Uneven |
| Hardness | 7 |
| Optic nature | Biaxial + |
| Refractive index | 1.66-1.68 |
| Birefringence | 0.015 |
| Dispersion | Low, 0.017 |
| Specific gravity | 3.18 |
| Lustre | Vitreous |
| Pleochroism | Strong |
Figure \(\PageIndex{1}\): Faceted Yellow Hiddenite
Photo courtesy of
Wild Fish Gems
| Spodumene image gallery |
Crystallography
Crystal system: monoclinic.
Habit: flattened and corroded prism with vertical striations, irregular capping reminiscent of Mountain range; sometimes massive. Generally long slender prismatic crystals, often etched.
Chemical composition
Lithium Aluminium Silicate (LiAl(SiO3)2).
Generally there is little Na present. Fe, Ca may replace Li; Cr may be present (Hiddenite green)
Diagnostics
Color and varieties
Hiddenite: yellow green to emerald green (due to Cr).
Kunzite: clear lilac, pink, violetish, purplish (due to Mn).
Other (Spodumene): Yellow, colourless, gray, blue (yellows due to Fe).
Magnification
Complex three phase inclusions characteristic of of spodumene; cleavages; growth tubes; needle like etch tubes; twin planes; crystals.
Luminescence
Very strong fluorescence: golden pink to orange under LWUV and weaker under SWUV.
Sometimes phosphorescent.
Pleochroism
Strong.
There is generally a strong absorption along the c-axis.
Specific gravity
Spodumene sinks in heavy liquid 2.88.
Treatments
- Irradiation (colorless to pink, other colors).
- Heat treatment (green purple or pink to lighter).
Simulants
| Spodumene | |
|---|---|
| Name | Key separations |
| Euclase | Slightly lower S.G., UV fluorescence |
| Sillimanite | Inclusions, generally inert under UV, higher birefringence |
| Tourmaline | S.G. (lower heft), uniaxial character, Inclusions, R.I and D.R. |
| Thulite | Higher S.G., higher R.I. range and UV fluorescence |
| Rose Quartz | Lower S.G, R.I. |
| Natural Spinel | Singly refractive nature, magnification, spectrum |
| Hiddenite | |
|---|---|
| Name | Key separations |
| Emerald | Lower heft (floats in 2.88), uniaxial, R.I, D.R., magnification features |
| Chrysoberyl | Higher S.G. (heft), spectrum, R.I. |
| Diopside | Higher S.G., R.I., spectrum and stronger doubling of Back facet edges or inclusions |
| Kunzite | |
|---|---|
| Name | Key separations |
| Amethyst | Lower S.G. (floats 2.88), UV reaction unlike spodumene, bull's-eye optic figure, R.I. |
| Morganite | Lower S.G. (floats 2.88), uniaxial, R.I., magnification features |
| Topaz | Higher heft, low birefringence and UV reaction unlike spodumene |
| Pink sapphire | Higher heft, R.I higher and lower birefringence |
Occurrence
Geological occurrence: Spodumene occurs in granite pegmatites, sometimes with very great sizes.
Geographical occurrence: Mainly North and South America; Madagascar; Burma; Brazil. USA: N.Carolina (yellowish green)- hiddenite; Connecticut (lilac); CA (Kunzite); Coahulia Mountains (yellow, yellowish green, bluish pink) Madagascar: Kunzite, green, yellowish - Anjanabonoina. Brazil: Paler hiddenite, white spodumene, cat's eye, yellow to pale green, bluish pink Kunzite, yellow and green Burma: Spodumene from upper Mogok stone tract (blue) Afghanistan: Kunzite, yellow, blue and green.
References
- Gems Their Sources, Descriptions and Identification 4th Edition (1990) - Robert Webster (6th ed.)
- Colour Encyclopedia - J.E. Arem ISBN 0412989115