Page 75 - Atlas of Sedimentary Rocks Under The Microscope

Carbonate rocks

Dolomitization

Introduction

Dolomite. CaMg(C03)2, is a major component of limestones. It is
usually secondary. replacing pre-existing carbonate minerals. Unlike
calcite, it often occurs as euhedral rhomb-shapcd crystals. However.
since its optical properties arc similar to those of calcite, it can be
difficult to distinguish between the two. For this reason etching and
staining of sections with Alinrin Red S i s carried out (see p. 34).
Dolomitic rocks arc classified according to their dolomite content as
follows:
0 to 1 0% dolomite limestone
10 to 50% dolomite dolomitic limestone
50 to 90% dolomite calcitic dolomite
90 to 100% dolomite dolomite
Since the term dolomite is used for both the mineral and the rock, some
workers prefer the term dolos/One for the rock. although the term has
not been universally accepted and is not employed here.

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