PROUSTITE: Germany (7.53)
Proustite is one of the most sought-after of all collector minerals because of its magnificient color and the brilliance of good crystals. It is far too soft for wear, and exposure to light causes it to turn black (a photochromic effect due to the silver present) so the material should not be displayed in strong light. Faceted gems are deep red with a metallic surface that is both beautiful and distinctive. One of the rarest of all the better-looking collector gems.
Proustite Value
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Proustite Information
| Data | Value |
| Name | Proustite |
| Crystallography | Hexagonal (R). Crystals prismatic,rhormbohedral; massive, compact. |
| Colors | Deep red, scarlet to vermilion red. |
| Luster | Adamantine to submetallic. |
| Hardness | 2-2.5. |
| Birefringence | 0.296. |
| Cleavage | Distinct 1 direction. Fracture conchoidal to uneven. Brittle. |
| Stone Sizes | Most cuttable proustite is from Chile, but cuttable crystals in private collections and museums are not about to be cut up. Occasional fragments from Germany are transparent. Gems weighing several hundred carats could be cut from crystals on display in various museums. The finest proustites known are in the collection of the British Museum of Natural History, London. Smithsonian Institution (Washington, D.C): 9.9 (red, Germany). |
| Luminescence | None. |
| Spectral | Not diagnostic. |
| Formula | Ag3AsS3 |
| Pleochroism | Strong in shades of red. |
Dimorph of Xanthoconite.
Streak: Bright red.
Optics: o= 3.088; e= 2.792.
Uniaxial (—).
Occurrence: Low-temperature ore deposits or the upper portions of vein deposits.
Idaho; Colorado; Nevada; California.
Sarrabus, Sardinia.
Cobalt district, Ontario, Canada: small crystals.
Batopilas, Chihuahua, Mexico: small crystals.
Freiberg, Germany: fine crystals; other German localities, sometimes in very fine and large crystals, some cuttable.
Dolores Mine, Chanarcillo, Chile: world‘s finest proustite occurs here, in crystals of deep red color, often transparent, up to 6 inches long and very thick. The occurrence here is unique.
Comments: Proustite is one of the most sought-after of all collector minerals because of its magnificient color and the brilliance of good crystals. It is far too soft for wear, and exposure to light causes it to turn black (a photochromic effect due to the silver present) so the material should not be displayed in strong light. Faceted gems are deep red with a metallic surface that is both beautiful and distinctive. One of the rarest of all the better-looking collector gems.
Name: After J. L. Proust, a French chemist.
