Abstract

Saponite

A soft, soapy earth, varying in color from nearly white to greenish and bluish colors, has been known for more than a hundred and fifty years. It has been called soapstone and porcellanous earth. It was found to fill cavities in rocks, and especially in those rocks that contain little or no potassium, such as basic trap rocks. It is a hydrous silicate of alumina and magnesia, essentially, but with a little iron and sometimes a little lime, and its optical elements have not been ascertained (System of Mineralogy). To this mineral Dana referred several species that were studied later and whose optical characters were determined, at least in part, and which had a similar origin, such as bowlingite, thalite, and some glauconite. Bowlingite was found to be derived directly from an alteration of olivine, one of the common magnesian minerals of basic igneous rock.2 Thalite was found to have an internal

First Page Preview

First page PDF preview
You do not currently have access to this article.