Sussexite

An attractive mass of pinkish-lavender, cherty sussexite rimmed by buff-colored calcite in a matrix of hydrothermally altered ore. The calcite in the ore has been colored reddish-brown by the partial hydrothermal breakdown of franklinite to form microscopic, disseminated grains of hematite. The parallel fractures in the sussexite are joints, geologically akin to the common but much larger joints often seen in rock exposures. Joints can form in minerals as well as rocks and are most likely to form in minerals that are mechanically homogeneous, either because they lack cleavage (e.g., franklinite, garnet) or because they have formed as compact, very fine-grained aggregates, as here. This specimen is no. ERV-116 in the collection of Earl R. Verbeek.

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