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16.11: Spodumene

  • Page ID
    4313
  • 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.