Proustite Value, Price, and Jewelry Information
Proustite crystals have magnificent red colors and good brilliance. Although facetable, they're too soft for jewelry use but highly desired as collector's gems.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Hexagonal (R). Crystals prismatic, rhombohedral; massive, compact.|
|Colors||Deep red, scarlet to vermilion red.|
|Luster||Adamantine to submetallic.|
|Fracture||Conchoidal to uneven|
|Specific Gravity||5.51 - 5.64|
|Cleavage||Distinct 1 direction|
|Transparency||Opaque to translucent, some crystals transparent.|
|Absorption Spectrum||Not diagnostic.|
|Phenomena||Proustite with silver may be photochromic.|
|Pleochroism||Strong in shades of red. Blood red/scarlet.|
|Optics||o = 3.088; e = 2.792. Uniaxial (-).|
|Etymology||After Joseph L. Proust, the French chemist who identified this mineral.|
|Occurrence||Low-temperature ore deposits or the upper portions of vein deposits.|
One of the rarest of all the better-looking collector gems, faceted proustite can display deep red colors with a beautiful and distinctive metallic surface luster. Sometimes called “ruby silver,” proustite is also a source of ore for this metal. (Of course, “ruby” here refers strictly to proustite’s color, since these minerals are unrelated).
Proustites and xanthoconites are dimorphous. They share a chemical formula, but proustites have hexagonal (trigonal) crystal habits, while xanthoconites have monoclinic habits. Proustite also forms a series as the arsenic (As) analogue to pyrargyrite, the antimony (Sb) analogue.
The presence of silver in proustite causes a permanent photochromic effect. Exposure to light over time turns it black.
No known treatments or enhancements.
Chile produces the world’s finest proustite, particularly from the Dolores Mine in Chanarcillo. Deep red, often transparent crystals occur here in sizes up to 6 inches long and very thick. The occurrence here is unique. Most cuttable gem material comes from Chile.
Freiberg, Germany also produces fine crystals. Other German localities sometimes yield very fine, large, cuttable crystals and, occasionally, transparent fragments.
Other notable gem sources include the following:
- Cobalt district, Ontario, Canada: small crystals.
- Batopilas, Chihuahua, Mexico: small crystals.
- United States: California; Colorado; Idaho; Nevada.
- Czech Republic; Peru; Sarrabus, Sardinia.
Faceters could cut gems weighing several hundred carats from crystals displayed in various museums and private collections. However, that likely won’t happen. The National History Museum in London holds some of the finest specimens known. The Smithsonian Institution holds a 9.9-ct red stone from Germany.
Faceters should note that proustite does contain arsenic. When cutting this gem, take care not to accidentally ingest dust or particles from it. For more information, consult our articles on general safety tips for lapidaries and advice for handling toxic gem materials. However, wearing or handling finished proustites should pose no health problems.
Due to its photochromism, don’t display this gem material under strong light. Furthermore, the stone’s very low hardness (2-2.5) makes it a very impractical choice for a jewelry piece. (A coin could scratch it). Consult our gemstone jewelry cleaning guide for more recommendations.