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Millerite occurs in relative abundance with chalcopyrite, pentlandite, violarite, pyrrhotite, and sparse pyrite in discontinuous stringers and disseminations along fractures and joints in leucocratic and amphibolitic footwall gneisses near the norite contact more than 3,000 feet below the present surface. Some roughly equidimensional masses up to 8-10 centimeters in size show splendent crystal faces and excellent cleavages barred by polysynthetic twinning. Gangue minerals include sodic and potassic feldspar, quartz, amphibole, epidote, garnet, and biotite. Partial chemical analysis on handpicked cleavage fragments of millerite gave 62.0% Ni, 0.04% Cu, 0.33% Co, and 1.44% Fe. The x-ray powder diffraction pattern gave a0 = 9.622 ± 0.006A and c. = 3.150 ± 0.005A. Primary origin by crystallization from a hot sulphur-rich iron-poor fluid is proposed from the environmental evidence available.
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