2 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
LEVERRIERITE GOUGE FROM THE BLACK JACK MINE, IDAHO. 
The first specimen to be examined (Museum Cat. 24679) was 
labeled ‘“‘tallow clay, Black Jack vein, Carson district, Owyhee 
County, Idaho.’’ This proved to consist of the peculiar aluminous 
silicate leverrierite. Exact details in regard to the occurence of the 
clay are not obtainable. Lindgren mentions‘! clayey minerals at sev- 
eral points in this vein. Where the vein is exposed at the surface by 
trenches small streaks of quartz and valencianite with comb struc- 
ture appear, stained and incrusted by hematite and limonite and im- 
bedded in soft brownish rhyolite, often with considerable masses of 
clay, resembling kaolin. In the granite the vein is intimately con- 
nected with a basaltic dike averaging 2 feet in width which is per- 
pendicular or dips steeply west. Although the dike is often soft and 
clayey, its walls are always sharply defined and are separated from 
the granite or the vein by clay seams. The vein lies on the footwall 
or hanging wall of the dike or both, with an average width of 10 
inches. A sharp contact with clay gouge separates vein from dike 
but the gangue is not uncommonly frozen to the granite. The lower 
part of the vein is in granite while the upper part is in extrusive 
rhyolite. The gangue consists of quartz and valencianite while the 
principal ore minerals are black finely divided argentite and chal- 
copyrite which is highly auriferous. 
Physical properties —The specimen, which has been cut into a rec- 
tangular block while plastic, is smooth and resembles a hard soap. 
Its exterior is pale pink, the color obviously being due to discolor- 
ation or darkening on exposure as the interior is snowy white. The 
structure is laminated and platy but suggests schistosity rather than 
micaceous cleavage such as was found in the Colorado leverrierite. 
There are air holes in the Idaho material which indicate that the 
material was originally moist and and very plastic and that the speci- 
men was kneaded somewhat while in this condition. When placed 
in water the material softens slowly and cracks up gradually. At 
the end of several hours immersion it had not disintegrated in the 
manner characteristic of bentonite. Its hardness in the specimen is 
about 1. The mineral has every appearance of a soaplike amorphous 
clay. When crushed between the teeth there is an absolute absence 
of any grit and, when in its original moist condition, the consistency 
must have been such as to make the name ‘‘tallow clay” exceedingly 
appropriate. 
1 Waldemar Lindgren. Gold and Silver Veins in Idaho. 20th Annual Report, U. S. Geol. Survy., 
pt. 3, pp. 135-140, 1899. 
