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Peretaite

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Peretaite
General
CategorySulfate
Formula
(repeating unit)
Ca(SbO)2(SO4)2(OH)2 · 2H2O
IMA symbolPta[1]
Crystal systemMonoclinic
Identification
ColorColorless, can be pink
Crystal habitPrismatic crystals
TwinningVery common on {100}
CleavagePerfect on {100}
Mohs scale hardness3.5-4
LusterVitreous
StreakWhite
DiaphaneityTransparent
Specific gravity4.06
Density3.8 g/cm3
Optical propertiesbiaxial positive
Refractive indexnα= 1.686 nβ= 1.694 nγ= 1.709
PleochroismStrong with colors pink(γ') to green(α')
Ultraviolet fluorescenceNo
References[2]

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

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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.[2] 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.

Physical properties

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The mineral peretaite has transparent crystals that are colorless. It has a vitreous luster and perfect {100} cleavage. The density of peretaite was determined by a heavy-liquid method, crystals tend to float in a Clerici solution, which has a density of 4.0 g/cm3, therefore the density is 3.8 g/cm3.[2]

Chemical properties

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The mineral is made up of 4 oxides. Most of this mineral is made up of an Antimony oxide, Calcium, and a sulfur oxide. Some of the qualitative analyses of peretaite were done by an ORTEC X-ray microanalyzer and an ARL SEMQ electron microprobe.[2] Later it was discovered that the crystals would disintegrate under the electron beam. Therefore, a wet chemical analysis was performed for the sulfur content, calcium was determined by atomic absorption, and antimony was determined by alternating current anodic stripping voltammetry.[2]

Chemical Analysis in Weight %
Oxide Ideal weight percentage Analytical Results
Sb2O3 68.31 69.09
CaO 6.58 6.44
SO3 18.78 17.62
H2O 6.33 6.0

Crystallography

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X-ray single-crystal study indicated peretaite had a symmetry of 2/m with a space group of C2/c or Cc and a crystal system of monoclinic.

See also

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References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d e Nicola Cipriani, Silvio Menchetti, Paola Orlandi, Cesare Sabelli, 1980, "Peretaite a new mineral from Pereta, Tuscany, Italy", American Mineralogist, vol 65, pg 936-946.