Sulphosalt of antimony and arsenic
Specific gravity: 5.91 calculated
Common impurities: Ag,Cu
Sterryite is of hydrothermal origin, occurring in marble
At the type locality, the Taylor Pit, Huntingdon Township, Madoc area, Hastings County, Ontario, Canada, sterryite is rare, but it has been found both in polished sections and as loose fragments. In the sections, sterryite has been observed as needlelike laths which cut veenite parallel to its direction of polysynthetic twinning, and as single anhedral grains also associated with veenite. Sterryite has not been observed in contact with any other minerals. Loose fragments are plumose and characteristically occur as bundles of fibres. The small fragments of sterryite available are black in colour and streak (CM 9.191-213).
At the Pollone mine, Valdicastello Carducci, Pietrasanta, Lucca Province, Tuscany, Italy, the deposit lies where metamorphic rocks outcrop surrounded by non-metamorphic sedimentary formations.
Sterryite and parasterryite cannot be distinguished under the microscope. Sterryite, more common than parasterryite, occurs as lead-grey prismatic crystals, elongate and striated, usually up to a few mm long, but exceptionally up to 3 cm. Crystals are usually included in quartz or baryte, but in some cases it is possible to find crystals inside small vugs of the baryte matrix. Sterryite is generally superficially altered to earthy black products. In polished section, small areas of famatinite are closely associated to a large crystal of sterryite. These two minerals require different conditions for their formation, and this indicates non-equilibrium conditions, probably two distinct stages in the mineral succession (CM 49.623-638).
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