Fes. 1900. NEw MINERAL OCCURRENCES—FARRINGTON. 22 
9 
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 f-2R. 
This symbol is sufficiently established by the relation of the cleav- 
age rhombohedron to the crystal form and by several measurements 
Saiup rom 10? 25°*to 101° 35’ :for'f- f—o0221 , 2021. The ‘cal- 
culated value is 101° g’. 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 ie 
prisms varies from a few milli- 4 
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 intwodirec- yg. g~Golden Calcite. 
tions, so that an apparently ‘flattened rhombohedron 
ee Calcite. results. The planes of such crystals show a curvin 
af g 
