158 FieLp CoLuMBIAN MusEumM—GEocoey, Vot. III. 
This is also usually truncated by the positive % rhombohedron d 
(o1l2). The unit prism m, (1olo) also appears as small planes. The 
third specimen (Mus. No. M 10276) consists of a large crystal of ortho- 
clase 3x5 inches in size more or less intergrown with albite, and show- 
ing also three crystals of topaz 2 to 3 inches in length. . Scattered 
about upon the albite and orthoclase about 50 crystals of phenacite 
occur. These vary in diameter from 1 cm. tO“D Mines 
whitish to colorless, the larger crystals tending to be semitrans- 
parent and the small ones perfectly transparent. In habit all show 
the lenticular shape previously described, which is produced by 
the forms already mentioned. Many of the smaller crystals, how- 
ever, are more highly modified than the large ones and. the planes 
being brilliant and giving good reflections afford easy identification 
of the forms. The following is a list of the forms observed and some 
of the measurements obtained: 
m (1olo) d (o1l2) S$ (ea3n) 
a. (1120) Po (T122) Saal cen 
tou) | 
Observed Calculated 
Qi NOP = SOT TeO) ef ano Le = S8° Tan 58° 78/ 
tN OD es (LOLT): Waa aa a ZO. Tae PO as 
ee hate Gite GA hu bide fas = so° Ai 52° 39 
m' A -d == forlo) way foria) =. 65” 258 69° 37" 
fh. Oa eee (VOLT ee ore = 31° 35s a aes 
Y UR ASY vets CIOL) ay ee Tea) = chee hey) 20.5 
SUAS Pe a (2737 eae oe ae 55° 40> 050 meas 
The appearance of one of the crystals is shown in the accompany- 
ing figure, Fig. 4, it having been drawn as is usual with phenacite, 
with the negative rhombohedrons in front. 
REALGAR 
MERCUR, UTAH 
PLATES XLIV AND LIV 
Among other specimens from Mercur, Utah, obtained from May- 
nard Bixby, two exhibiting realgar deserve especial mention. In 
one of these specimens (Mus. No. M 8204), the realgar occurs as small 
crystals partially filling a narrow fissure in limestone: in the other 
(Mus. No. M 820s) it occurs as elongated prisms intergrown with 
