Stability of Minerals in Sedimentary Rocks

Abstract

AS the rocks which form the continental masses are disintegrated by the action of weathering and other geological agents, their detritus accumulates to form sedimentary rocks, ultimately on the sea-bed. In most instances, the constituents of these sedimentary rocks afford a clue to the character of the parent material and furnish information about the probable source and direction of transportation of the detritus (provided, of course, that the investigation is carried out over a sufficiently wide area). In the majority of sediments, especially the coarser types, the bulk of the grains consist, however, of the common mineral quartz, which yields little evidence of a particular source, for it is widely distributed throughout almost all types of rocks. It is able to survive many cycles of erosion because of its high resistance to chemical alteration and mechanical disintegration. But certain other constituents, usually of rarer occurrence, known as the heavy detrital minerals because of their higher density (>2 9), are of much greater value as clues to origin, for many of them are characteristic of particular rock-types.