peretaite

{{Infobox mineral |name=Peretaite |category=Sulfate |formula=Ca(SbO)2(SO4)2(OH)2 · 2H2O | IMAsymbol = Pta |system=Monoclinic |color=Colorless, can be pink |habit=Prismatic crystals |twinning=Very common on {100} |cleavage=Perfect on {100} |mohs=3.5-4 |luster=Vitreous |refractive=nα= 1.686 nβ= 1.694 nγ= 1.709 |opticalprop=biaxial positive |pleochroism=Strong with colors pink(γ') to green(α') |fluorescence=No |streak=White |gravity=4.06 |density=3.8 g/cm3 |diaphaneity=Transparent | references = }} Peretaite is a sulfate of antimony and calcium. The mineral, Ca(SbO)4(SO4)2(OH)2 (2(H2O)), was named Peretaite for its locality. It was first discovered in an antimony-bearing vein at Pereta, Tuscany, Italy.

== Occurrence == Peretaite occurs in only small quantities, as aggregates of tabular crystals. The crystals are found in the geodes of a deeply silicified limestone. It also occurs in the cavities of columnar stibnite. Other associated minerals are stibnite, quartz, calcite, pyrite, valentinite, kermesite, sulfur, and gypsum. Peretaite can often be red from the inclusion of valentinite. The mineral was formed by the action of sulfuric acid on the stibnite; peretaite is closer to the boundary of the country rock limestone, which is the source of the calcium in peretaite.