WesternDevil from lt [GFDL or CC-BY-SA-3.0], from Wikimedia Commons
This is not a terribly attractive gemstone, but faceted gems would be a tremendous rarity. The material is quite brittle, but there is no cleavage to cause problems in cutting. I do not know of the existence of a faceted gem at this writing.
| Data | Value |
|---|---|
| Name | Gadolinite |
| Crystallography | Monoclinic. Crystals rough and coarse often terminated; massive. |
| Crystallographic Forms | |
| Refractive Index | 1.77-1.82 |
| Colors | Black, greenish black, brown, very rarely light green. |
| Luster | Vitreous to greasy. |
| Hardness | 6.5 - 7.0 |
| Fracture | Conchoidal |
| Specific Gravity | 4.0-4.65 (usually 4.4); metamict material 4.2. |
| Birefringence | High, and variable 0.01-0.04. |
| Cleavage | None |
| Stone Sizes | Norwegian crystals have been found up to 4 inches across and nodules up to 60 pounds have been unearthed in Texas. This massive material cuts cabochons up to several pounds. Faceted gems, however, would be very tiny and very rare since the mineral is rarely transparent, even in thin splinters. |
| Transparency | Opaque. Very rarely transparent, even in thin splinters. |
| Formula | Be2FeY2Si2O10 |
| Optics | a = 1.77-1.78; γ = 1.78-1.82. Biaxial ( + ), 2V = 85°. Usually metamict and amorphous, hence isotropic. |
| Optic Sign | Biaxial + |
Streak: Greenish gray.
Optics: a = 1.77-1.78; γ= 1.78-1.82.
Biaxial ( + ), 2V = 85°. Usually metamict and amorphous, hence isotropic.
Occurrence: Granites and granite pegmatites. Colorado; Texas; Arizona.
Greenland; Sweden; Norway; USSR; Japan; Switzerland; Australia.
Comments: This is not a terribly attractive gemstone, but faceted gems would be a tremendous rarity. The material is quite brittle, but there is no cleavage to cause problems in cutting. I do not know of the existence of a faceted gem at this writing.
Name: After the Swedish chemist, J. Gadolin.
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