Sanidinite Facies

metamorphic rocks formed by contact metamorphism under conditions of high temperature and low pressure.

The products of metamorphism in contacts with extrusive and subvolcanic igneous rocks are classed with sanidinite faciès. Under these conditions, argillaceous schists are transformed into rocks with high-temperature potassium feldspar (sanidine) called sanidinites; calcareous rocks (marls and basic extrusives) become metamorphic forms composed of high-temperature, potassium-rich silicates, for example, larnite Ca₂[SiO₄] and wollastonite, and carbonate-silicates, such as spurrite Ca(SiO₄)₂CO₃ and tilleyite Ca₅(Si₂O₇[CO₃]₂).

Subfacies of the sanidinite facies are identified by associations of calcium-bearing minerals: spurrite or larnite (formed at the highest temperature, above 1,100°C), tilleyite (1,100°-1,000°C), calcite-wollastonite-monticellite or calcite-akerman-ite (1,000°-900°C), and diopside-calcite-wollastonite (below 900°C).

REFERENCES

Fatsii metamorfizma. Moscow, 1970.
Marakushev, A. A. Petrologiia metamorficheskikh gornykh porod. Moscow, 1973.
Eskola, P. “The Mineral Facies of Rocks.” Norsk Geologisk Tidsskrift, 1921, vol. 6.

A. A. MARAKUSHEV

单词	sanidinite facies
释义	Sanidinite Facies Sanidinite Facies metamorphic rocks formed by contact metamorphism under conditions of high temperature and low pressure. The products of metamorphism in contacts with extrusive and subvolcanic igneous rocks are classed with sanidinite faciès. Under these conditions, argillaceous schists are transformed into rocks with high-temperature potassium feldspar (sanidine) called sanidinites; calcareous rocks (marls and basic extrusives) become metamorphic forms composed of high-temperature, potassium-rich silicates, for example, larnite Ca₂[SiO₄] and wollastonite, and carbonate-silicates, such as spurrite Ca(SiO₄)₂CO₃ and tilleyite Ca₅(Si₂O₇[CO₃]₂). Subfacies of the sanidinite facies are identified by associations of calcium-bearing minerals: spurrite or larnite (formed at the highest temperature, above 1,100°C), tilleyite (1,100°-1,000°C), calcite-wollastonite-monticellite or calcite-akerman-ite (1,000°-900°C), and diopside-calcite-wollastonite (below 900°C). REFERENCES Fatsii metamorfizma. Moscow, 1970. Marakushev, A. A. Petrologiia metamorficheskikh gornykh porod. Moscow, 1973. Eskola, P. “The Mineral Facies of Rocks.” Norsk Geologisk Tidsskrift, 1921, vol. 6. A. A. MARAKUSHEV
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