Difference between revisions of "Diaspore"
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Diaspore as a plausible gemstone has been reported first around 1977 when a large enough crystal was examined at the Gem Testing Laboratory in London. This, usually colorless, material showed good color-change from pale bluish-green to pale pinkish-brown. Turkey was the origin of this color-change material. | Diaspore as a plausible gemstone has been reported first around 1977 when a large enough crystal was examined at the Gem Testing Laboratory in London. This, usually colorless, material showed good color-change from pale bluish-green to pale pinkish-brown. Turkey was the origin of this color-change material. | ||
When Zultanite Gems LLC aquired the mining location, this color-change variety of diaspore was marketed under the tradename "zultanite®". At present (2007) sole distribution rights of "zultanite®" are granted to GemsTV. | When Zultanite Gems LLC aquired the mining location, this color-change variety of diaspore was marketed under the tradename "zultanite®". At present (2007) sole distribution rights of "zultanite®" are granted to GemsTV. | ||
+ | |||
+ | ==Chemical composition== | ||
+ | AlOOH + Mn (or Fe) as impurity (a dimorph of boehmite).<br /> | ||
+ | Mn or Fe may substitute Al in the lattice. | ||
+ | |||
+ | ==Crystallography== | ||
+ | Orthorhombic. | ||
+ | Habit: crystals are elongated plates (tabular); acicular needles also massive; foilated. | ||
+ | |||
+ | ==Diagnostics== | ||
+ | |||
+ | Diaspore may be confused with [[peridot]] due to the strong doubling of back facets, but diaspore is usually much paler in color. Iron-rich green sapphire has an absorption sectrum close to sapphire. | ||
+ | |||
+ | ===Color=== | ||
+ | Colorless, pale bluish-green to pale green, pale pinkish-brown to pale brown. | ||
+ | |||
+ | ===Diaphaneity=== | ||
+ | Transparent to opaque. | ||
+ | |||
+ | ===Specific Gravity=== | ||
+ | S.G.:3.2 - 3.5 (mean = 3.4) | ||
+ | |||
+ | ===Cleavage=== | ||
+ | Perfect in one direction {010} and imperfect on {110} and {210}. | ||
+ | |||
+ | ===Refractometer=== | ||
+ | Optic nature: Biaxial positive.<br /> | ||
+ | Refractive index range: n<sub>α</sub> = 1.682 - 1.702, n<sub>Β</sub> = 1.705 - 1.725 and n<sub>γ</sub> = 1.730 - 1.752. Mean = 1.702 - 1.750.<br /> | ||
+ | Maximum birefringence: 0.040 - 0.048. | ||
+ | |||
+ | ===Spectrum=== | ||
+ | Not diagnostic but Turkish stones 471, 463, 454 (much similar to iron-rich sapphire). | ||
+ | |||
+ | ===Luminescence=== | ||
+ | UV fluorescence: May show dull pale yellow (LW) and green (SW) | ||
+ | |||
+ | ===Pleochroism=== | ||
+ | Strong depending on body colour and source. Blue / Pale green and rose to dark red. | ||
+ | |||
+ | ==Simulants== | ||
+ | |||
+ | {| {{table}} width="70%" style="margin-left:0" | ||
+ | |- | ||
+ | | [[Sapphire]] || No strong doubling of facets; higher heft; higher R.I., unixial figure. | ||
+ | |- | ||
+ | | [[Sillimanite]] || Lower S.G., lower RI and lower birefringence. | ||
+ | |- | ||
+ | | [[Peridot]] || Lower RI and slightly lower birefringence. | ||
+ | |} | ||
+ | |||
+ | ==Occurrence== | ||
+ | |||
+ | Geological occurrence:<br /> | ||
+ | In metamorphosed limestones, chloritic schists and altered igneous rocks. Also in bauxite deposits. | ||
+ | |||
+ | Geographical locations:<br /> | ||
+ | Memaris, Turkey (gemmy pale brown); Chester, Massachusetts (with corundum); Pennysylvania (fine transparent colourless to brown); Hungary; South Africa in Postmasburg district - Manganiferous variety; Cornwall, England; Greenland; Norway; Sweden; France; Switzerland; Germany; Greece; USSR; Japan; China; Turkey. | ||
+ | |||
+ | ==References== | ||
+ | * ''Gems, Their Sources, Descriptions and Identification'' 4th ed. (1990) - Robert Webster ISBN 0750658568 (6th ed.) | ||
+ | * ''Colour Encyclopedia'' - J.E. Arem ISBN 0412989115 | ||
+ | * ''Textbook of mineralogy'' - E.S. Dana | ||
+ | * ''Introduction to Optical Mineralogy'' (2004) - William D. Nesse ISBN 0195149106 |
Revision as of 10:54, 30 August 2007
Diaspore | |
---|---|
Chemical composition | AlO(OH) |
Crystal system | Orthorhombic |
Habit | Tabular, sometimes fibrous |
Cleavage | Perfect to imperfect |
Fracture | Conchoidal |
Luster | Bright vitreous to pearly (on cleavage surface). |
Hardness | 6.5 - 7 |
Optic nature | Biaxial + |
Refractive index | 1.682 - 1.752 |
Birefringence | 0.040 - 0.048 |
Specific gravity | 3.2 - 3.5 |
Lustre | Vitreous |
Pleochroism | Moderate |
Diaspore as a plausible gemstone has been reported first around 1977 when a large enough crystal was examined at the Gem Testing Laboratory in London. This, usually colorless, material showed good color-change from pale bluish-green to pale pinkish-brown. Turkey was the origin of this color-change material.
When Zultanite Gems LLC aquired the mining location, this color-change variety of diaspore was marketed under the tradename "zultanite®". At present (2007) sole distribution rights of "zultanite®" are granted to GemsTV.
Contents
Chemical composition
AlOOH + Mn (or Fe) as impurity (a dimorph of boehmite).
Mn or Fe may substitute Al in the lattice.
Crystallography
Orthorhombic. Habit: crystals are elongated plates (tabular); acicular needles also massive; foilated.
Diagnostics
Diaspore may be confused with peridot due to the strong doubling of back facets, but diaspore is usually much paler in color. Iron-rich green sapphire has an absorption sectrum close to sapphire.
Color
Colorless, pale bluish-green to pale green, pale pinkish-brown to pale brown.
Diaphaneity
Transparent to opaque.
Specific Gravity
S.G.:3.2 - 3.5 (mean = 3.4)
Cleavage
Perfect in one direction {010} and imperfect on {110} and {210}.
Refractometer
Optic nature: Biaxial positive.
Refractive index range: nα = 1.682 - 1.702, nΒ = 1.705 - 1.725 and nγ = 1.730 - 1.752. Mean = 1.702 - 1.750.
Maximum birefringence: 0.040 - 0.048.
Spectrum
Not diagnostic but Turkish stones 471, 463, 454 (much similar to iron-rich sapphire).
Luminescence
UV fluorescence: May show dull pale yellow (LW) and green (SW)
Pleochroism
Strong depending on body colour and source. Blue / Pale green and rose to dark red.
Simulants
Sapphire | No strong doubling of facets; higher heft; higher R.I., unixial figure. |
Sillimanite | Lower S.G., lower RI and lower birefringence. |
Peridot | Lower RI and slightly lower birefringence. |
Occurrence
Geological occurrence:
In metamorphosed limestones, chloritic schists and altered igneous rocks. Also in bauxite deposits.
Geographical locations:
Memaris, Turkey (gemmy pale brown); Chester, Massachusetts (with corundum); Pennysylvania (fine transparent colourless to brown); Hungary; South Africa in Postmasburg district - Manganiferous variety; Cornwall, England; Greenland; Norway; Sweden; France; Switzerland; Germany; Greece; USSR; Japan; China; Turkey.
References
- Gems, Their Sources, Descriptions and Identification 4th ed. (1990) - Robert Webster ISBN 0750658568 (6th ed.)
- Colour Encyclopedia - J.E. Arem ISBN 0412989115
- Textbook of mineralogy - E.S. Dana
- Introduction to Optical Mineralogy (2004) - William D. Nesse ISBN 0195149106