2 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
UNUSUAL PYRITE CRYSTALS FROM ARKANSAS. 
A specimen recently received for examination from Mr. C. A. 
McClelland of Stillwater, Ark., contains pyrite crystals of such un- 
usual development as to merit a brief description. The crystals are 
small, averaging less than a millimeter in diameter, and are attached 
to the faces of imperfect quartz crystals which line vuggy cavities in 
white quartz. The quartz forms veins up to 2 inches thick in a 
black highly graphitic slate. No other minerals are associated with 
the pyrite. The crystals all show the simple combination of cube 
a(100) and octahedron 0(111) both prominently developed. Their 
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Figs. 1-5.— PYRITE CRYSTALS FROM STILLWATER , ARK. 
claim to distinction lies in their unsymmetrical development. Many 
of the crystals are cuboctahedrons of normal proportions. (Fig. 1.) 
From this habit they vary to long prismatic with the length 10 to 20 
times the diameter as illustrated in Figure 3, the apparently tetrag- 
onal prism being formed by the vertical faces of the cube, while the 
octahedral planes form a terminal pyramid, often truncated at its 
summit by a minute cube face. The faces are practically perfect 
and free from striations, although some of the long prisms taper 
slightly, as indicated by the following angular measurements, which 
were made on a crystal of the habit illustrated in Figure 3. 
