rocks and the occasional mineral
BY DOMINICK HENRICKSEN
below and on the earths surface
intrusive and extrusive intrusive are formed in side the earth and extrusive are formed on the earths surface
A pegmatite is a intrusive igneous rock composed of interlocking phaneritic crystals usually larger than 2.5 cm in size such rocks are referred to as pegmatitic. Most pegmatites are composed of quartz, feldspar and mica, having a similar basic composition asgranite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene, feldspathoids and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions
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.
Phyllite is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation. It is primarily composed of quartz, sericite mica, and chlorite.
Phyllite has fine-grained mica flakes in a preferred orientation, whereas slate has extremely fine clay flakes that achieve a preferred orientation, and schist has large flakes in a preferred orientation. Among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist