Quartz Quartz is hexagonal and commonly occurs as crystals ranging in size form microscopic to crystals weighing several tons. Where it crystallizes unhindered by other crystals, such as in cavities in rock or in a liquid containing few other crystals, it shows well-developed hexagonal prisms and sometimes showing apparent hexagonal pyramids or dipyramid. When it crystallizes in an environment where growth is inhibited by the surroundings, it rarely show crystal faces. It is also found as microcrystalline masses, such as in the rock chert, and as fibrous masses, such as in chalcedony. Vitreous lusture. As visible crystals, Quartz is one of the more common rock forming minerals. It occurs in siliceous igneous rocks such as volcanic rhyolite and plutonic granitic rocks. It is common in metamorphic rocks at all grades of metamorphism, and is the chief constituent of sand. Because it is highly resistant to chemical weathering, it is found in a wide variety of sedimentary r
Meteorites - chunks of rock from space that land on Earth. Meteors are not meteorites Like meteorites, meteors are objects that enter Earth's atmosphere from space. But meteors-which are typically pieces of comet dust no larger than a grain of rice-burn up before reaching the ground. Common minerals in meteorites : · kamacite, · taenite (both Ni-Fe alloys, different crytall structures) · pyroxene (especially bronzite) · olivine · plagioclase Kinds of meteorites : v irons v stones v stony-irons Iron meteorites : Predominantly Ni-Fe alloys Minor amounts of other minerals such as troilite (FeS) Types classified according to % Ni: Hexahedrite octahedrite (has Widmanstatten structure, exsolution feature formed by slow cooling) ataxite Stone meteorites : Chiefly silicates, mostly ferromagnesian Up to 1/4 metallic Ni-Fe Types: Chondrites Achondrites Chondrites : Contain chondrules (BB-si