Volume 22, pages 931-933, 1937

      Sodium and chlorine are commonly found in the deep mine waters¹ of the Michigan Copper Mines. Halite has been mentioned² but once and then only as a few crystals found on the 9th level of the Hecla Mine.

      The mineral occurs in the form of stalactites, stalagmites and encrustations on the walls as well as on the floor. There are even a few slabs as large as a foot square and two inches thick. The halite varies from coarse crystals of about one inch cubes to very fine thread-like crystals. These fine crystals are so fragile and delicate that even a slight breeze loosens them from the walls and produces what appears to be falling snow. The larger needle-like crystals show square terminations; in other words, they are distorted cubes. Although the large crystals are cubes, many are modified by octahedrons, as shown in Fig. l. They have a salty taste, perfect cubical cleavage, hardness of 3, and a specific gravity of 2.11. The low gravity is probably due to air bubble inclusions. Most of the material is coated with yellow-reddish mine sludge that washes off very readily, leaving the crystals pure white. There are also other encrustations, some red, others green; but not enough of these have been collected for determinative work.

     
FIG. 1. Halite showing cube in combination with the octahedron.

      The brown-colored material was analyzed by R. F. Makens as follows: It was washed and dried to constant weight at 110°C. The resulting material consisted of nearly colorless cubic crystals. A qualitative analysis showed traces of Fe⁺⁺⁺ Ca⁺⁺ and SO4^-- associated with relatively large amounts of Na⁺ and Cl^-. 0.07% of the original material was found to be insoluble in water.

      The Na⁺ was determined quantitatively as NaZn(UO₂)₃(C₂H₃O₂)₉·6H₂O according to the directions of H. H. Barber and I. M. Kolthoff,³ and the chloride was determined by precipitating and weighing as silver chloride. The per cent Na⁺, found as an average of five determinations, was 39.5%; and the per cent Cl^-, found as an average of two determinations, was 60.76%. The theoretical percentages of Na⁺ and Cl^- in pure NaCl are 39.32% and 60.68%, respectively.

      X-ray diffraction patterns⁴ of the Quincy halite and known sodium chloride were identical.

      The part of the 85th level where the halite was found in such abundance has not been in use for six years, and the drift is subject to a continuous air current. As the walls, floors, and crevices are covered with halite in a manner similar to the occurrences of calcium carbonate in limestone caves, it is believed that the halite was precipitated by evaporation from waters as they oozed from crevices in the rock or concentrated in small pools on the floor.

NOTES

      1 Dripping on 55th level north of No. 6 shaft, Quincy Mine