The Mineral pearceite

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. 

Chemical Formula

[(Ag₉CuS₄)][(Ag,Cu)₆As₂S₇]

Color

Dark gray to nearly black. May have occasional internal red reflections.

Crystal System

Monoclinic

Properties

Streak Black. May have a red tinge.

Hardness 2.5 - 3

Transparency Opaque

Specific Gravity 6.0 - 6.2

Luster Metallic

Cleavage 1,3

Fracture Uneven

Tenacity Brittle

Crystal Habits

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.

3D Crystal Atlas

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Additional Information

Composition Silver and copper arsenic sulfide, often with some antimony

In Group Sulfides; Sulfosalts

Striking Features Crystal habits, streak, and mode of occurrence.

Rock Type Sedimentary, Metamorphic

Other Names

Arsenpolybasite

Uses

Pearceite is as an ore of silver.

Noteworthy Localities

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.

Common Mineral Associations

Polybasite, Quartz, Calcite, Barite, Acanthite, Tetrahedrite, Silver, Proustite

Distingushing Similar Minerals

Polybasite - Indistinguishable without complex methods.

pearceite Photos

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