Sanidine

tectosilicate

hornfels

Formula: K(AlSi3O8) tectosilicate (framework silicate)
Sanidine is a high-temperature K-feldspar.
Specific gravity: 2.53 to 2.56
Hardness: 6
Streak: White
Colour: Colourless, transparent to opaque grey, grey brownish
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Volcanic igneous environments
Pegmatites

Sanidine occurs as phenocrysts (larger crystals embedded in a finer-grained matrix in an igneous rock) in volcanic igneous rocks such as rhyolite and trachyte. It is characteristic of rocks that cooled quickly from an initial high temperature of eruption.

Sanidine may occur in hornfels.

It is characteristic of the sanidinite facies.
Common impurities: Fe,Ca,Na,H2O

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