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Microcline: Mineral Information Page

See also the rare Microcline feldspar variety Amazonite, and the rare orthoclase variety Moonstone

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In the earth's crust, feldspars are more abundant than all other minerals combined. The majority of the common feldspars fall into two groups, the alkali feldspars (KAlSi3O8 through NaAlSi3O8 series), and the plagioclase feldspars (NaAlSi3O8 through CaAl2Si2O8 series). Microcline (KAlSi3O8) is the low temperature pure potassium end member of the alkali feldspar group.

At high temperatures, the alkali feldspars form a continuous solid solution series, however at medium to low crystalization temperatures the sodium feldspar (albite) and potassium feldspar (microcline or orthoclase) separate forming lattice type exsolution intergrowths, usually as thin layers of albite roughly parallel to {100} in a host crystal of microcline or orthoclase. This is known as perthitic texture. Adularia is an unusual gem variety of the potassium feldspar orthoclase. It exhibits an iridescence most commonly known as moonstone (also known as adularescence), which is due to diffused light reflection from microscopic parallel intergrowths of albite and orthoclase.

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Microcline commonly occurs in plutonic igneous rocks such as granites and syenites that cooled slowly and at considerable depth. It is the common potasium feldspar variety in pegmatites where it can form the largest known crystals of any mineral (in a pegmatite in Karelia, U.S.S.R., a microcline mass weighing over 2000 tons showed the form of a single crystal!). Microcline and quartz (often as smoky quartz) can crystalize simultaneously in pegmatites in an interpenetrating pattern known as graphic granite. The rare variety of green microcline known as amazonite also occurs in pegmatites. Its green color is thought to be due to trace impurities of lead and OH-1. Microcline is also common in metamorphic rocks in gneisses, and in sedimentary rocks in arkoses and conglomerates.

Microcline is distinguished in thin section from orthoclase (the medium temperature polymorph of potassium feldspar which is chemically identical to microcline) by the presence of tartan twinning. In the field the indicators are color, transparency, occurance and luster.

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The name microcline comes from two Greek words meaning little and inclined, referring to the cleavage angle's slight inclination from ninety degrees. Feldspar is derived from the German word feld which means field.

The green variety of microcline amazonite is used as an ornamental lapidary material.
Microcline is used mainly in the manufacture of porcelain. It is ground very fine and mixed with kaolin and quartz. Upon heating, the feldspar fuses and acts as a cement binding the materials together. Fused feldspar also is the main constituent in the glaze on porcelain. Sometimes feldspar is also used to supply alumina in the manufacture of glass.

The astrological sign of microcline is Libra.
The astrological sign of amazonite is Virgo.
Amazonite is an alternate birthstone for the month of December.

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Microcline is said to stimulate clarity of thought, to enhance understanding, and to improve one's ability to cooperate with others. Microcline is also said to help treat eye disorders and fevers. It also is said to control water retention and to help with ease of childbirth.
Amazonite is said to calm one's emotions and soothe nerves, and to enhance creativity and the ability to express oneself. The deeper the color of the amazonite, the more intense the effect is said to be. Amazonite is said to help aleviate muscle spasms and to help normalize calcium levels in the body, and to help relieve stress and exhaustion.

For more in-depth metaphysical information, see our Metaphysical Books section.

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Last Updated: March 17, 2015
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