ORPIMENT

ABOUT THE SPECIMEN

For all of the nice orpiment specimens to have come out of the Quiruvilca Mine, not too many have reached the impressive size and presence that this one has. With large crystals and a balanced appearance, all on matrix, this represents a distinctly high quality of specimen. Standard for orpiment from here, there’s a fair share of bruising, although in this case it reveals an underlying layer of growth with a shining golden luster. Comes with an old label attached.

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Set at roughly 3,800 meters in the Peruvian Andes, Quiruvilca exploits epithermal and mesothermal Cu-Pb-Zn veins hosted in Miocene Calipuy Formation andesites and basalts, with four concentric mineralogical zones radiating outward from a central enargite core. Orpiment precipitated within that innermost zone as a low-temperature arsenic sulfide alongside enargite, pyrite, and the locality's celebrated hutchinsonite - arsenic bonding with sulfur in a layered monoclinic structure that intrinsically produces the saturated yellow-orange color without requiring any trace chromophore. Crystals occur as translucent to transparent prismatic blades and foliated masses with a distinctly resinous luster, frequently on pyrite matrix; the combination of orpiment with hutchinsonite on a single specimen is a Quiruvilca signature with no meaningful parallel elsewhere. Most significant pocket finds date to the 1970s and a secondary pulse in the late 1990s, both from the now largely flooded enargite zone. The material bruises readily given orpiment's perfect cleavage and softness, meaning pristine pieces were a small fraction of recoveries even when the zone was active - a structural fragility that has steadily thinned available quality over the decades since mining shifted to the outer Pb-Zn zones.