152 FiELD CoLuMBIAN MusEuM—GEo Loey, Volt. III. 
OLIVENITE 
TINTIC DISTRICT, UTAH 
PLATE Lib 
Crystals of olivenite from this locality have been previously de- 
scribed by Washington,* but a large suite of specimens received from 
Maynard Bixby affords some new characters which seem worthy 
of description. The olivenite in these specimens occurs both as well- 
defined crystals and in the fibrous form known as wood-copper. For 
the most part the crystals present the dark olive-green color char- 
acteristic of olivenite, although there are some variations from this, 
as will be noted. None of the crystals is highly modified, nor are they 
of large size. For the most part they exhibit a prismatic habit and 
occur encrusting cavities in a cupriferous gangue. The largest crystals 
noted (Mus. No. M 9414) are represented by Fig. 1, Pl. LII. These 
crystals are scattered in radiated fashion over a siliceous matrix and 
reach in some cases a length of 1 cm. They are usually attached 
by the macropinacoid a (100). As shown in the figure, they are 
simple in form, being made up of the unit prism m (110), the 
macropinacoid a (100) and the brachydome d (025). This dome isa 
form new to olivenite. Its determination was based on a good meas- 
urement of d A d’ = 32° 45’. A somewhat similar habit is ex- 
hibited by the crystals shown in Fig. 2, Pl. LII (Mus. No. M 9400), 
except that the basal plane occurs here and the macropinacoid 
is lacking. The dome and base are characterized by striations 
|| to a (100). These crystals are of dark, nearly black, color, about 
1 mm.in length and occur thickly encrusting a somewhat porous 
gangue. Another simple habit consists only of the unit prism and 
basal plane, producing a tabular form. This is exhibited in Fig. 3, 
Pl. LII (Mus. No. M 9413). These crystals occur lining a cavity about 
one inchin diameter. Sheaf-like crystals of azurite of a tabular habit 
are implanted upon the olivenite. The olivenite crystals are of a light 
olive-green color, with dull planes, and are usually attached by the 
basal plane. The average length of these crystals, measured in 
the direction of the macro-axis is 5mm. A rather unusual habit for 
olivenite is that represented in Fig. 4, Pl. LIZ (Mus. No. M g4ar). 
These crystals are elongated in the direction of the brachy-axis. 
The extension seems to be rather the result of growth of a number of 
* Am. Jour. Sci., 1888, 3, 35, p. 208. 
