Pearceite

Characteristics of Pearceite

Pearceite is often granular and massive; crystals are short, tabular pseudohexagonal prisms with bevelled edges, showing triangular striations on faces parallel to the plane containing the a and b axes, and rosettes of such crystals, to 3 cm across. The mineral is black, and in polished section it is white with very dark red internal reflections. It has a black to reddish black streak and a metallic luster, generally opaque, but translucent in very thin fragments. It is biaxial with a very high refractive index of 2.7 and maximum birefringence δ also 2.7. Dispersion of the optic axes is relatively strong. Reflected light anisotropism is the property of appearing to change color when viewed under crossed polarised light in a reflected light microscope. Pearceite exhibits moderate anisotropism, often dark violet. The color in reflected plane polarised light is white, with very dark red internal reflections and very weak pleochroism in air, fair in oil. Reflectivity in air at 540 nm is about 30%. It is not fluorescent. Pearceite is a brittle mineral that breaks with a conchoidal to irregular fracture. It is soft, with hardness only 3, the same as calcite. The silver content gives it a high specific gravity of 6.15, the highest of the ruby silvers. Cleavage is either absent or poor. The mineral is neither magnetic nor radioactive.