Argentopyrite
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Sommaire
COLOR
Light brown : at first glance, very similar to pyrrhotite. Pleochroism is strong, ranging from light yellow-brown to darker brown.
REFLECTANCE
Very high : definitely higher than ruby silvers, much lower than pyrrhotite.
ANISOTROPISM
Strong in both forms. Tints are multicolored (unlike pyrrhotite) and range from reddish brown to light green with purple-pink shades for sternbergite (by uncrossing the nicoles, characteristic blue tints are commonly observed). Argentopyrite has slightly duller brown to greenish grey-white tints. By uncrossing the nicols, red-brown, pink and light green-yellow tints somewhat similar to sternbergite but without its characteristic blue tints are observed.
TEXTURE
Both minerals show cleavages but they are particularly well developed in sternbergite and are a reliable criterion of determination. Cleavage in sternbergite is somewhat similar to that observed in graphite or molybdenite and like those minerals, sternbergite is very often twisted and sinuous.
ASSOCIATED MINERALS
Various silver minerals, pyrite, nickel-cobalt arsenides, native silver.
CRITERIA OF DETERMINATION
Rather similar to pyrrhotite but wich a much stronger pleochroism and more distinctly colored anisotropism. The association with other silver minerals is also a distinctive characteristic. Both minerals (argentopyrite and sternbergite) are clearly dinstinguishable. Sternbergite has a more distinctly colored anisotropism (shows blue tints under crossed nicols) and perfectly developed cleavage not observable in argentopyrite. It does not take as good a polish and is more readily deformed than argentopyrite.
Source
ATLAS OF ORE MINERALS (P. Picot and Z. Johan)
