Argentite

Argentite

COLOR

Light grey with a greenish shade somewhat similar topolybasite. Scratches are common. Very weak pleochroism.

REFLECTANCE

Rather low. Definitely lower than galena. May not seem as bright as it really is because of abundant scratches.

ANISOTROPISM

Distinctly visible though weak. By uncrossing the nicols, the tints are rather characteristic, ranging from purplish slate-blue to greenish. Light corrosion by arc lamp is very striking, almost as rapid as for canfieldite. It may vary considerably from one specimen to another.

TEXTURE

Argentite shows very abundant twin lamellae. These polysynthetic twins result from an inversion from cubac (alpha-Ag2S) to (beta-Ag2S) which indicates a temperature of deposition above 179°C. Thus, they are useful as a geological thermometer. Argentite often replaces galena, either froming a rim around it or in the fractures or cleavages (cementation argentite). Very often, argentite is associated with native silver.

ASSOCIATED MINERALS

Native silver and other silver minerals; galena.

CRITERIA OF DETERMINATION

Poor polish, greenish tint, purplish blue-green to green polarization colors and rapid corrosion in light. By comparison with polybasite which also corrodes rapidly in light, polarization tints are completely different and internal reflections are lacking. Jalpaite takes a better polish, in slightly creamy and is not purplish under crossed nicols. Instead, brownish tints not occurring in argentite are observe. Aguilarite has a slightly higher reflectance, takes a better polish and does not corrode in light.

Source

ATLAS OF ORE MINERALS (P. Picot and Z. Johan)