Habit
Zinc schefferite forms coarse granular or foliate masses, mixed with willemite and franklinite. A basal parting, due to lamellar twinning parallel to the base, is so perfect as to give the mineral a foliated appearance strongly suggesting feldspar, and there is also a poor parting parallel to the orthopinacoid. The cleavage is good parallel to the prism and in traces parallel to the clinopinacoid. The hardness is 5.5, and the specific gravity is 3.3 to 3.39. The color ranges from white (very rarely) to light brown and rich dark brown. The optic axis is approximately normal to the base. Bx_a/\ c' = 4° 35' in obtuse angle. The indices are a = 1.876 ±0.0008, b = 1.683 ±0.0006, g = 1.705 ±0.0008, for sodium light. 2V = 60° 0', r > v.

Composition
Analyses 4 and 5 (see page 62) show that the mineral is close in composition to jeffersonite, from which it differs chiefly in the practical absence of iron and in the greater amounts of calcium and magnesium and less amounts of manganese and zinc.

Occurrence
At Franklin zinc schefferite was abundant in massive ore in parts of the Parker shaft workings. It was first described by Wolff (185), from whose paper the data given above were taken. The same material had previously been analyzed by Hillebrand (183), who, however, had not separated the mineral from jeffersonite.

With the development of mining at Sterling Hill on a large scale and the operation of a separate mill, zinc schefferite has been found abundantly in the ore there. As it is nonmagnetic it comes out in milling with the willemite.


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