Sanidine

minerals

muscovite

K-feldspar

hornblende

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Formula: K(AlSi3O8)
Tectosilicate (framework silicate), feldspar group, fully disordered in its Al and Si distribution, paramorph of kokchetavite, microcline (fully ordered) and orthoclase (partially ordered). Sanidine forms a series with high albite (disordered, stable above 800oC) (Mindat).
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
Common impurities: Fe,Ca,Na,H2O
Environments:

Volcanic igneous environments

Sanidine is a high-temperature K-feldspar; it 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.

Associated minerals include quartz, sodium-rich plagioclase, muscovite, biotite, hornblende and magnetite (HOM).

Localities

The type locality is Drachenfels, Königswinter, Rhein-Sieg-Kreis, Cologne, North Rhine-Westphalia, Germany.

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