American Institute of Mining, Metallurgical, and Petroleum Engineers · New York (etc.) · leaf 227
ppear, and both these andthe well-bounded ones are generally badly decomposed. With quartzit forms the groundmass of most of the eruptive rock. Calcite is abundant as a secondary mineral, especially as a replace-ment of other minerals, notably feldspar. It may be one of the gangueminerals and… … Tourmaline, occasional grains in tuff. Biotite, occasional shreds, probably secondary. Sericite is the predominant alteration product of the groundmass, M. H. LOVEMAN 191 and away from the ore zone also of the feldspars. It occurs as a mat ofslender microscopic crystals. Kaolin is the principal…
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