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This group of minerals consists of three silicates: a potassium- aluminium silicate (the orthoclase feldspars), a sodium-aluminium silicate, and a calcium-aluminium silicate (the plagioclase feldspars) and their isomorphous mixtures.
Orthoclase (KAlSi3O8) is named based on the GreekThe Greek language ( /Elini'k{/) is an Indo-European language which has existed from around the 14th century BC in the Cretan inscriptions called Linear B. Mycenaean Greek of this period is distinguished from later Classical or Ancient Greek of the 8th ce for "straight fracture," because its two cleavages are at right angles to each other. Orthoclase crystallizes in the monoclinicIn crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. Two of crystal system. It has a hardnessMohs' scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created by the German mineralogist Friedrich Mohs and is one of several definitions of hardness i of 6, a specific gravity of 2.56-2.58, and a vitreous to pearly luster. It can be colored whiteAlternate meanings: White (disambiguation White is a color (more accurately it contains all the colors of the spectrum and is sometimes described as an achromatic color— black is the absence of color) that has high brightness but zero hue. The impression, grayGray or grey is a color seen commonly in nature. It is created by mixing white and black in different proportions. Depending on the amount of light, the human eye can interpret the same object as either gray or some other color. Two colors are called comp, yellowYellow is the color of light whose wavelength is between 565nm and 590nm, or is a mixture of red and green light that appears to be the same color. Yellow is one of the subtractive primary colours ( primary pigments), and its complementary color is blue. or redRed is a color at the lowest frequencies of light discernible by the human eye. Red light has a wavelength of roughly 700 nm. Oxygenated blood is red due to the presence of hemoglobin. Red light is the first to be absorbed by sea water, so that many fish; rarely green. Twin crystals are not uncommon. Orthoclase is a common constituent of most granites and other felsic igneous rocks and is often found in huge crystals and masses in pegmatite veins. Orthoclase is used in the manufacture of porcelain and as a constituent of scouring powder. Adularia (from Adular ) is found in low temperature hydrothermal deposits. When pearly and opalescent orthoclase is called moonstone and is used in jewelry. These opalescent varieties are known to be an intergrowth of orthoclase and albite. A glassy kind of orthoclase, called sanidine , is typical of felsic volcanic rocks and is found in the trachytes of the Drachenfels , Germany.
Microcline (KAlSi3O8) is chemically the same as orthoclase, but belongs to the triclinic crystal system, the prism angle being slightly less than right angles; hence the name "microcline" from the Greek "small slope." Microcline is identical to orthoclase in all physical properties and can be distinguished only by optical examination; under a polarizing microscope microcline exhibits a minute multiple twinning which results from a grating-like structure that is unmistakable. It is probable that much orthoclase is actually microcline. Amazon stone, or amazonite, is a beautiful green variety of microcline. It is not found anywhere in the Amazon basin, however, Spanish explorers who named it apparently confused it with another green mineral from that region.
A soda microcline named anorthoclase is known, which is an isomorphous mixture of KAlSi3O8 and NaAlSi3O8, the sodium-aluminium silicate being in larger proportion.
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