ROCKS

Listing description Breccia ( / ˈ b r ɛ t ʃ i ə / or / ˈ b r ɛ ʃ i ə / ; Italian : breach) is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix , [1] that can be either similar to or different from the composition of the fragments. Detailed description The word has its origins from Italian language , and in that language indicates either loose gravel or stone made by cemented gravel . A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, tectonic breccia, igneous breccia, impact breccia and hydrothermal breccia. Types Sedimentary Sedimentary breccias are a type of clastic sedimentary rock which are made of angular to subangular, randomly oriented clasts of other sedimentary rocks. They are formed by either submarine debris flows , avalanches , mud flow or mass flow in an aqueous medium. Technically, turbidites are a form of debris flow deposit and are ...

Listing Description: Amphibolite is the name given to a metamorphic rock consisting mainly of amphibole , especially the species hornblende and actinolite . A holocrystalline plutonic igneous rock composed primarily of hornblende amphibole is called a hornblendite , which are usually crystal cumulates . Rocks with >90% amphiboles which have a feldspar groundmass may be a lamprophyre . Detailed Description: Amphibolite is a grouping of rocks composed mainly of amphibole and plagioclase feldspars, with little or no quartz . It is typically dark-colored and heavy, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance. Amphibolites need not be derived from metamorphosed mafic rocks. Because metamorphism creates minerals based entirely upon the chemistry of the protolith , certain 'dirty marls ' and volcanic sediments may actually metamorphose to an amphibolite as...

Listing description Andesite is the name used for a family of fine-grained, extrusive   igneous rocks   that are usually light to dark gray in color. They often weather to various shades of brown and these specimens must be broken for proper examination. Andesite is rich in   plagioclase   feldspar   minerals   and may contain   biotite ,   pyroxene , or   amphibole . Andesite usually does not contain   quartz   or   olivine . Detailed description Andesite is typically found in lava flows produced by stratovolcanoes. Because these lavas cooled rapidly at the surface they are generally composed of small crystals. The mineral grains are usually so small that they cannot be seen without the use of a magnifying device. Some specimens that cooled rapidly contain a significant amount of glass, while others formed from gas-charged lavas have a vesicular or amygdaloidal texture. Where Does Andesite Form?   Andesi...

Listing Description: Other names: Anhydrous Gypsum Anhydrite is an evaporite mineral that occurs in extensive layered deposits in sedimentary basins where large volumes of sea water have been evaporated. It is typically interbedded with   halite , gypsum   and   limestone   in accumulations that can be up to hundreds of feet thick. On a much smaller scale, anhydrite can form in shoreline or tidal flat sediments from the evaporation of sea water.   Detailed Description: Anhydrite also occurs as a vein-filling mineral in hydrothermal deposits. It is deposited from solution, often along with   calcite and halite, as gangue in sulfide mineral deposits. Anhydrite is also found in the cap rock of salt domes and in cavities of trap rock. Anhydrite is an anhydrous calcium sulfate with a composition of CaSO 4 . It is closely related to gypsum which has a chemical composition of CaS0 4 . 2H 2 O. The worldwide abundance of gypsum greatly exceeds th...

Listing description Apatite   is a group of   phosphate minerals , usually referring to   hydroxylapatite ,   fluorapatite   and   chlorapatite , with high concentrations of   OH − ,   F −   and   Cl −   ions , respectively, in the   crystal . The formula of the admixture of the four most common   endmembers   is written as   Ca 10 ( PO 4 ) 6 (OH,F,Cl) 2 , and the crystal unit cell formulae of the individual   minerals   are written as Ca 10 (PO 4 ) 6 (OH) 2 , Ca 10 (PO 4 ) 6 (F) 2 and Ca 10 (PO 4 ) 6 (Cl) 2 . Detailed description The mineral was named apatite by the German   geologist   Abraham Gottlob Werner   in 1786, although the specific mineral he had described was reclassified as fluorapatite in 1860 by the German   mineralogist   Karl Friedrich August Rammelsberg . Apatite is derived from the Greek απατείν (apatein), which means to deceive or to be misleading, as...