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This crystal is mainly terminated by a rhombohedron of the third order, (x). With this form are associated the prisms of the first and the second order, (m) and (a); another rhombohedron of the third order, (s), and the two rhombohedrons of the first order, (r).

Phenacite

This crystal is mainly terminated by a rhombohedron of the third order, (x). With this form are associated…