16.11: Spodumene

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gemology
Gemology Project

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Spodumene
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