Feb. 1900. New Mineral Occurrences — Farrington. 



229 



GOLDEN CALCITE. 



BAD LANDS, SOUTH DAKOTA. MUSEUM No. M 5904. 



On breaking open the concretions found in beds of Fort Pierre 

 shale in the region of the Bad Lands, South Dakota, the internal 

 cavities are often found to be studded with crystals of calcite of a 

 more or less golden yellow color. While this occurrence of calcite 

 has been known for some time, the form of the crystals has not 

 heretofore received description. A large quantity of the crystals 

 having been collected by the Museum Expedition to the Bad Lands 

 of 1898, I have examined them with the following results: In form 

 the crystals are all simple rhombohedrons having the symbol /,-2R. 

 This symbol is sufficiently established by the relation of the cleav- 

 age rhombohedron to the crystal form and by several measurements 

 ranging from 101 25' to 101 35' for/ :/=o22i a 2021. The cal- 

 culated value is 101 9'. No planes could be found which were 

 suited to accurate measurement, even the most favorable giving only 

 dim and elongated reflections. The most interesting feature of the 

 crystal form is the distortion which it exhibits. Although some of 

 the crystals show a normal development of the rhombohedron, the 

 greater number are lengthened out along an axis normal to one of 

 the rhombohedral planes. The appearance is therefore that of a 

 monoclinic crystal made up of a prism and basal planes. This 

 apparent prismatic form is made more striking from the fact that 

 the crystal usually rises more or less perpendicularly from its plane 

 of attachment. The apparent basal plane is usually more or less 

 curved, and has a somewhat 

 pearly lustre. The prismatic 

 planes are often curved as well. 

 The length of the apparent 

 prisms varies from a few milli- 

 meters to about 2 centimeters. 

 The form of these crystals is 

 represented in Fig. 7. Another 

 form of distortion is shown in 

 Fig. 8. Here the lengthening 

 out has taken place in two direc- 

 tions, so that an apparently flattened rhombohedron 

 results. The planes of such crystals show a curving 



Fig. 8-Golden Calcite. 



Fig. 7— Golden 



7— Gold 

 Calcite. 



