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2005-05-26 12:03:39

Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. It is sometimes called "iron mica" and is found in granitic rocks, gneisses, and schists. Like other mica minerals, biotite has a highly perfect basal cleavage, its flexible sheets easily flaking off. It has a hardness of 2.5 - 3, a specific gravity of 2.7 - 3.1, is colored greenish to brown or black, and can be transparent to opaque. Biotite is occasionally found in large sheets, especially in...

2005-05-26 10:50:45

Gneiss is a common and widely distributed type of rock formed by high grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. Gneissic rocks are coarsely laminated and largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc. However, depending on their composition,...

2005-05-26 09:41:33

The mineral kyanite is an aluminium silicate of the sillimanite group (along with andalusite and sillimanite), also called alumino-silicate. It has the formula Al2O3·SiO2 (Al2SiO5). Its hardness varies widely depending on its crystallographic direction, from 5 to 7.5, and it has a specific gravity of 3.56-3.67. It is translucent, usually blue, but possibly white, gray, green, or black. It is usually found in long-bladed crystals or columnar to fibrous structures. Kyanite is used in...

2005-05-25 18:35:54

The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. By definition, schist contains more than 50% platy and elongated minerals, often finely interleaved with quartz and feldspar. The individual mineral grains in schist, drawn out into flaky scales...

2005-05-25 17:09:09

Slate is a fine-grained, homogeneous, sedimentary rock composed of clay or volcanic ash which has been metamorphosed (foliated) in layers (bedded deposits). Slate can be made into roofing shingles ('roofing slates' in the United Kingdom), because it has two lines of breakability: cleavage and grain. This makes it possible to split slate into thin sheets. Slate is mainly composed of quartz and muscovite (a mica), often along with biotite, chlorite, and hematite, or, less frequently,...

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Word of the Day
  • A person in a secondary role, specifically the second most important character (after the protagonist).
The word 'deuteragonist' comes from a Greek word meaning 'an actor of second-class parts'.