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Pearceite is an uncommon mineral containing silver and copper in its structure. It forms a series with Polybasite, with Pearceite being the arsenic-rich member and Polybasite being the antimony-rich member. It is often not possible to visually distinguish these two minerals from each other. Pearceite is named in honor of Dr. Richard Pearce (1837-1927), a Cornish-American chemist from Colorado. |
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Chemical Formula |
[(Ag9CuS4)][(Ag,Cu)6As2S7] |
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Composition |
Silver and copper arsenic sulfide, often with some antimony |
| Variable Formula |
[(Ag9CuS4)][(Ag,Cu)6(As,Sb)2S7] |
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Color |
Dark gray to nearly black. May have occasional internal red reflections. |
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Streak |
Black. May have a red tinge. |
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Hardness |
2.5 - 3 |
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Crystal System |
Monoclinic |
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Crystal Forms
and Aggregates |
As short tabular crystals, often pseudohexagonal in shape due to twinning on the prism-planes. Also platy, bladed, in rosettes, grainy, flaky, and massive. Crystals are often striated with triangular striation patterns. |
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Transparency |
Opaque |
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Specific Gravity |
6.0 - 6.2 |
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Luster |
Metallic |
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Cleavage |
1,3 |
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Fracture |
Uneven |
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Tenacity |
Brittle |
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In Group |
Sulfides; Sulfosalts |
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Striking Features |
Crystal habits, streak, and mode of occurrence. |
| Rock Type |
Sedimentary, Metamorphic |
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Popularity (1-4)
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4 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
2 |
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Pearceite is as an ore of silver.
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Pearceite is not a common mineral. Worldwide localities include Měděnec, Chomutov District, Bohemia, Czech Republic; the Uchucchacua Mine, Oyon Province, Lima Department, Peru; and the San Juan de Rayas Mine, Guanajuato, Mexico. In the U.S., Pearceite has come from the Mollie Gibson Mine, Aspen, Pitkin County, Colorado; and from Neihart, Cascade Co., Montana.
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Polybasite - Indistinguishable without complex methods.
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