The color of a mineral in its powdered form,usually obtained by rubbing the mineral against an unglazed porcelaintile to see the mark it makes. A mineral harder than the tile must bepulverized by crushing.
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The color of a mineral in its powdered form,usually obtained by rubbing the mineral against an unglazed porcelaintile to see the mark it makes. A mineral harder than the tile must bepulverized by crushing.