TWISTED MILLERITE CRYSTALS

 A. C. HAWKINS

      In the anthracite coal basin at Nanticoke, Pa., the Mills coal vein is cut by narrow stringers of white quartz. In cavities which are present in this quartz, occasional aggregates of millerite crystals are found. Some of the aggregates of millerite are radiated, while others are irregular, a mass of brilliant acicular, hair-like prisms, the longest of which measures about 2 cm.

      Among the most slender of the millerite crystals there are a number which show a helical twist; they appear like ribbons which have been twisted from both ends. The twist is either right or left handed in equal numbers of the crystals.

      It does not appear that the twisting can have been the result of mechanical causes, since the small twisted crystals are interspersed with thicker prisms which are not twisted. The phenomenon must have been caused by a natural tendency in the growth of the crystal. Professor Newhouse of Mass. Institute of Technology has informed the writer that millerite crystals have been found in quartz veins in a number of other coal mines, and that quite frequently they are twisted. A similar twisted condition has been noted in stibnite.

      Thanks are due to Mr. T. J. Arnott of the Glen Alden Coal Company for submitting the specimens.

      1 W. T. Schaller, The Crystal Cavities of the New Jersey Zeolite Region U.S.G.S. Bull. 832, 1932.