Quartzite is the metamorphic equivalent of quartz sandstones. Sometimes the boundaries of the original grains of sand are visible but they have become firmly cemented together. Thus quartzite is a light coloured, medium specific gravity, showing typical vitreous lusture and conchoidal fracture and sacchraoidal structure. The principal constituent is quartz and this is a non- foliated metamorphic rock. It is produced by thermal or regional metamorphism of arenaceous rocks such as sands, sandstone and quartz-veins.
These are the most perfectly foliated metamorphic rocks. These are gray to black, fine grained rocks composed of finely divided micaceous minerals as micas, chlorite etc. with minor quantities of quartz, feldspar etc. These are the metamorphic equivalents of shales and mudstones. Carbonaceous matter is usually found associated with slates. The rock is characterised by the development of extremely good close-spaced cleavage plane, which are called ‘slaty cleavages’.
These are strongly foliated rocks of medium to coarse crystalline texture. Foliation or schistosity is caused by parallel or nearly parallel alignment of micaceous minerals. The most common minerals in schists are quartz, feldspar and micas. These are propel by medium to high-grade of regional metamorphism of argillaceous or quartzo-argillaceous sediments.
It is a typical foliated metamorphic rock usually having alternate dark and light streaks or bands. The light coloured bands consist predominantly of light coloured minerals as quartz, feldspar etc”‘ whereas the dark bands consist of micaceous and/or the acicular ferromagnesian minerals. These rocks represent highest grade of regional metamorphism of quartz-felspathic rocks (granites) or quasi-argillaceous sediments.
This is a non-foliated metamorphic rock, which is the metamorphic equivalent of calcite, limestone or dolomite. It is a soft, compact, sacchraoidal rock. The texture is massive granular.
It is a hard, compact, fine grained rock composed principally of quartz, micas, iron-oxide etc., in which the typical parallel texture of regionally metamorphosed crystalline schists is absent. These are non-foliated, dense and usually dark coloured metamorphic rocks.