http://geology.frequentlyasked.info Just another WordPress weblog Mon, 24 Sep 2007 15:47:08 +0000 http://backend.userland.com/rss092 en Hrematite, or Specular Iron, is ferric oxide, Fe203. Sp. gr. = 4.5-5.3; H = 6.5. Crystallizes in rhombohedrons, or more commonly, in nodular masses, which are composed internally of very flat crystals. The color is black or steel-grey, which becomes red when the mineral is finely powdered. Hsernatite frequently ... http://geology.frequentlyasked.info/2007/09/24/iron-minerals/ Calcite, carbonate of lime, CaC03, Sp. gr. = 2.72; H = 3. This mineral crystallizes in the hexagonal system, in a great variety of forms; rhombohedrons and scalenohedrons are common; hexagonal prisms and pyramids less so. Cleavage is very perfect, parallel to the faces of a rhombohedron, and the ... http://geology.frequentlyasked.info/2007/09/21/calcareous-minerals/ Chlorite Under this name are grouped a number of closely allied minerals, which are hydrated silicates of alumina, magnesia, and iron. They are soft minerals, with a hardness of 1-1.5 and a specific gravity of 2.6-2.96, and are of a green color. The crystalline form is somewhat uncertain, but is ... http://geology.frequentlyasked.info/2007/09/20/talc-and-chlorite-groups/ Olivine is the only mineral of this group of sufficient importance to require mention; it is a silicate of magnesia and iron 2 (MgO, FeO)Si02, though the percentage of iron varies greatly. Sp. gr. = 3.2-3.5; H = 6.5-7. Olivine crystallizes in the orthorhombic system, and occurs in prisms, flat ... http://geology.frequentlyasked.info/2007/09/19/olivine-group/ These two groups contain parallel series of minerals of similar chemical composition, but differing in their crystalline form and physical properties. In composition they are silicates of various protoxide bases, and range from silicates of magnesia to those of lime and lime-alumina, while silicate of iron is present in ... http://geology.frequentlyasked.info/2007/09/18/amphibole-and-pyroxene-groups/ These minerals have a complex chemical composition, and are so variable that it is difficult to give formulae for them; they are silicates of alumina, together with potash, lithia, magnesia, iron, or manganese. There is a difference of opinion regarding the crystalline system to which the micas should be ... http://geology.frequentlyasked.info/2007/09/17/mica-group/ These minerals are very closely allied to the felspars in chemical composition, but differ from them in crystalline form and physical properties. They have a much more restricted distribution than the felspars, but have, nevertheless, an important bearing upon the classification of certain groups of rocks in which they ... http://geology.frequentlyasked.info/2007/09/14/the-felspathoid-group/ Silica is an acid and forms a very extensive series of compounds with various metallic bases. As rock-forming minerals the silicates are second only to the silica minerals in importance. The Felspar Group The felspars are essentially silicates of alumina (Al2O3) together with potash, soda, or lime. Three primary felspars occur: ... http://geology.frequentlyasked.info/2007/09/13/minerals-composed-of-silicates/ Next to oxygen, silicon is by far the most abundant constituent of the earth's crust, though never occurring alone. It is united with oxygen to form silica (Si02) or enters into the formation of more complex compounds. The oxide, silica, is the commonest mode of occurrence and forms the ... http://geology.frequentlyasked.info/2007/09/12/minerals-composed-of-silica/ Of the simple, undecomposable substances, which chemists call elements, and of which somewhat more than seventy have been identified on the earth, only about twenty enter at all largely into the composition of the earth's crust,' so far as this is accessible to examination. It is estimated that 97 ... http://geology.frequentlyasked.info/2007/09/11/rock-forming-minerals/