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Abstract

Staining techniques are among the fastest, simplest, and cheapest methods for getting reliable data on composition of detrital grains or cements in sandstones. Stains for calcite, organic matter, K-feldspar, and plagioclase are among the most useful stains.

The top photo shows a sandstone (Pennsylvanian Tensleep of Wyoming; 0.10 mm) which has been stained for calcite using Alizarin Red S. Calcite and dolomite are both present as cements but only the calcite has taken the red stain. Note imperfections in staining of calcite near thin edges of crystals and where bubbles were present. Because of the similarity in optical properties of calcite and dolomite, such staining is essential for accurate identification of these minerals.

The lower photo shows a K-feldspar (sanidine) from a Tertiary intrusive in Nevada (0.28 mm). This originally colorless grain was stained for potassium using a sodium cobaltinitrite solution. The lack of twinning and cleavage in this grain make it difficult to differentiate from quartz without time-consuming optical study. Staining, however, provides a rapid and reliable alternative for routine petrographic studies.

Directions for stain preparation are given in the references by Bailey and Stevens (1960), Laniz, et al (1964), Dickson (1966), Friedman (1971), and Whitlatch and Johnson (1974).

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