Pinnoite

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Pinnoite
Pinnoite-179852.jpg
Pinnoite clusters from a salt dome in the Atyrau Oblast, Kazakhstan
General
CategoryBorate mineral
Formula
(repeating unit)
MgB2O(OH)6
Strunz classification6.BB.05
Crystal systemTetragonal
Crystal classPyramidal (4)
H-M symbol: (4)
Space groupP42
Unit cella = 7.617 Å, c = 8.19 Å; Z = 4
Identification
ColorColorless, light yellow, yellow green
Crystal habitShort prismatic crystals uncommon; radial fibrous clusters
FractureUneven
Mohs scale hardness3.5
LusterVitreous
DiaphaneityTranslucent
Specific gravity2.27
Optical propertiesUniaxial (+)
Refractive indexnω = 1.565 nε = 1.575
Birefringenceδ = 0.010
References[1][2][3]

Pinnoite is a magnesium borate mineral with formula: MgB2O(OH)6[2][1] or MgB2O4·3(H2O).[3] It crystallizes in the tetragonal crystal system and occurs as colorless to yellow or light green radial fibrous clusters and rarely as short prismatic crystals.

Pinnoite was first described in 1884 for an occurrence in the Stassfurt potash deposit, Saxony-Anhalt, Germany and named for the mine counselor Oberbergrat Pinno of Halle, Germany.[2][1] It occurs in marine evaporite deposits and as efflorescence associated with mineral springs. It occurs with boracite and kaliborite.[2] It also occurs in the borax mines of Death Valley in California, the Da Quidam saline lake of the Qinghai-Xizang Plateau in Tibet and in Socacastro, Salta Province, Argentina.[2][1]

References[edit]