The polishing of many sections of chalcocite, digenite, and covellite on the lead lap has shown that physical changes can take place which may affect the interpretation of textures, and that special care should be exercised in polishing this group of minerals. The changes are probably attributable to two causes: (1) a mechanical dragging and smearing of these minerals into each other, and (2) some type of surficial solid solution which is induced under the conditions encountered during polishing. The effects may be avoided by careful polishing on a cloth lap, but even with the cloth lap too much pressure must not be used. Most of the physical changes would probably be noticed during a microscopical examination, but "blue chalcolite" which might easily escape detection can be formed.

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