orthoclase feldspar

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Related to orthoclase feldspar: microcline, adularia, biotite

orthoclase feldspar:

see feldsparfeldspar
or felspar
, an abundant group of rock-forming minerals which constitute 60% of the earth's crust. Chemically the feldspars are silicates of aluminum, containing sodium, potassium, iron, calcium, or barium or combinations of these elements.
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References in periodicals archive ?
The feldspar fraction is dominantly altered orthoclase feldspar and perthitic ortho-clase feldspar with traces of microcline and plagioclase.
After obtaining the key to the farm gate, we proceeded to the pocket where large (greater than 10-cm) orthoclase feldspar crystals had been excavated, together with schorl and yellow hyaline opal.
The grains are dominated by monocrystalline non-undulose quartz, minor polycrystalline quartz, less orthoclase feldspar, some rock fragments, micas and a suit of heavy minerals.