Corundum occurs as an accessory mineral in some metamorphic rocks, such as mica schist, gneiss , and crystalline limestone.
Quarzitic gneiss , low-grade metamorphic basic rocks, phyllites and dark chert can be abundant in some layers.
The sample is weakly banded amphibolite-facies gneiss consisting of quartz, plagioclase, biotite and hornblende.
Between the Dharwas leucogranite and Kilar there is a simple planar structure of interspersed pelitic gneiss and leucogranite bands with a regional foliation dipping to the south or southeast.
The Borve Series is dominated by varieties of quartzo-feldspathic schist and gneiss , composed mainly of plagioclase, quartz, and biotite.
The youngest is yellowish-orange to yellowish-gray arkose, derived primarily from Precambrian gneissoid and granitoid rocks; it contains little clay, abundant calcium carbonates, and limonite cement, and is host for all uranium deposits of the district.
The tonalite is gneissic , banded on a decimetre scale, and loaded with discrete mafic enclaves, metasedimentary xenoliths and garnet, feldspar and rutile xenocrysts, such that the body has a migmatitic appearance.
This intrusion is not sharply defined everywhere and in many places the gneissoid foliation of the Yonkers granite blends so intimately with the gneiss of the Fordham formation that sharp, clear-cut contacts cannot be seen.
In the inner sulfide zone gneissoid textures resulting from complete and vigorous replacement of the country rock have resulted.
There are also gray and fine grained red granites, and in some places they have taken a gneissoid form.