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A dense siliceous rock having the texture, dull luster, hardness,
conchoidal fracture, and general appearance of unglazed porcelain; it is
less hard, dense, and vitreous than chert. The term has been used for: an
impure chert, in part argillaceous; an indurated or baked clay or shale
often found in the roof or floor of a burned-out coal seam; and a
fine-grained, acidic tuff compacted by secondary silica. Etymol: Italian
porcellana, porcelain. Also spelled: porcelanite; porcelainite.
See also: siliceous shale; porcelain jasper;
haelleflinta. AGI
Source:
Dictionary of Mining, Mineral, and Related Terms
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