Explanation
A class of metamorphic rock with obvious gneissose structure. The composition minerals mainly include feldspar, quartze and dark minerals, and the content of feldspar is often higher than that of quartze. Dark minerals are biotite, amphibole, pyroxene, etc., with a total content of more than 15%. Sometimes it contains metamorphic minerals such as sillimanite, garnet, kyanite and cordierite. The mineral grain size is generally coarse (larger than lmrn), and the gneissose structure is typical, sometimes in the form of eye ball or banded structure. According to mineral assemblage and characteristics, it can be divided into hornblende plagioclase gneiss, hornblende lherzolite plagioclase gneiss, biotite monzonite gneiss, epidote albite gneiss, dolomite potash feldspar gneiss, corundum sillimanite gneiss, garnet biotite syenite gneiss, graphite gneiss, jadeite gneiss, etc. The original rock type of gneiss is complex, and it is usually called orthogneiss from intermediate acid intrusive rocks or volcanic rock. It is called paragneiss, which is changed from arkose, greywacke, calcareous mud rock, clay rock, semi muddy and semi sandy rock or tuffaceous rock of corresponding composition. gneiss often contains mica, graphite, feldspar, garnet, corundum, kyanite and other useful minerals. Some gneiss have bright colors and beautiful patterns, which are good building or decorative stones.
Classification
Natural materials and products -> Mineral materials