Arsenic

COLOR

White with a creamy tint. Pleochroism is fairly weak. Takes a rather good polish with few scratches. After a few days tarnishes very rapidly to a brownish grey which darkens very quickly.

REFLECTANCE

High but definitely lower than the other native elements. Much lower than antimony. Somewhat similar to pyrite.

ANISOTROPISM

Strong but in rather noncharacteristic tints: yellowish, bruwnish or greyish (tints are a little more distinc and more orange colored at low magnification). Antimony is similar to arsenic under crossed nicoles but has more intense orange tints. Numerous scratches invisible in ordinary light become visible under crossed nicols.

TEXTURE

Arsenic is characterized by particularly numerous and frequently intersecting polysynthetic twins and a perfectly developed cleavage. Rhytmic textures are rather common, as are concentric envelopes. Myrmekitic association with allemontite is rather common and highly characteristic.

ASSOCIATED MINERALS

Allemontite, bismuth, silver, dyscrasite, silver sulfosalts, argentopyrite.

CRITERIA OF DETERMINATION

The main criteria are: softness, relatively low reflectance for a native element, polysynthetic twins and especially rapid tarnishing. Antimony does not tarnish, has a much higher reflectance and polarizes in brighter orange tints. Dyscrasite has stronger reflectance, tarnishes far less rapidly and does not show twin lamellae. Moreover, its anisotropism is much weaker.

Source

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