In sedimentary rocks it occurs as detrital material.
The rocks at the base of the slopes are granite, the upper escarpments are of sedimentary rocks.
They are typical products of "regional" metamorphism, and are in nearly all cases older than the fossiliferous sedimentary rocks.
It consists of a series of plateaus formed of sedimentary rocks which mainly belong to three formations of widely separated ages, and which rest on a platform of granitic and metamorphic rocks.
They occur (a) in crystalline igneous and metamorphic rocks as an original constituent, (b) in veins associated with igneous rocks, and (c) in sedimentary rocks either as organic fragments or in secondary concretionary forms.