THE MINEKALS OF IDAHO 401 



CAMAS COUNTY 



Titanite occurs prominently in a black sand placer concentrate 

 from Bear Creek, Camas County. The crystals, which are minute 

 vary from pale yellow to greenish in color and show the familiar 

 "envelope" habit bounded by the forms c(001), a(100) and n(lll). 



CLEARWATER COUNTY 



Small yellow crystals similar to the last occur commonly in a 

 placer sand concentrate from Cow Creek in the Pierce district. 



VALLEY COUNTY 



Titanite is present in numerous crystals in a coarse-grained red 

 granitic rock sent from West Mountain in Valley County by I. W. 

 Phillips, of Pocatello. The CTystals reach an extreme diameter of 

 4 mm. and range from honey yellow or reddish yellow to black. 

 They have the usual envelope habit, but show smaller modifying 

 faces of a number of other and less common forms. 



BRANNERITE (519a) 



Hydratecl rnetatitanate of Uranium, etc. Orthorhombic or tetragonal. 



CUSTER COUNTY 



The new mineral brannerite has recently been described as material 

 from a gold placer worked by Henry Sturkey in Stanley Basin in the 

 central part of Idaho. 13 The placer from which the mineral came is 

 near the head of Kelly Gulch in western Custer County. The bed- 

 rock in the gulch is said to be granite cut by pegmatite. The branner- 

 ite is probably derived from one or more dikes of the pegmatite. 



The mineral occurs in the form of grains part of which are prisms 

 and most of which show a prismatic tendency (see pi. 13). They are 

 brownish yellow on the outside but the visible weathering has ex- 

 tended to a depth not exceeding the thickness of paper. Inside they 

 are a brilliant black, with a conchoidal fracture and no sign of cleavage 

 Polished specimens examined under reflected light show the mineral 

 to be remarkably homogeneous. It is, however, traversed by minute 

 cracks which are in part filled with quartz that undoubtedly accounts 

 for the silica shown in the analysis. Although to the eye the mineral 

 is opaque black, under the microscope very thin chips allow sufficient 

 yellowish-green light to pass to make possible optical measurements. 

 The streak is a dark greenish-brown. The hardness is about 4.5, as 

 the mineral will scratch apatite but will not scratch orthoclase. The 

 crystals are not perfect enough to allow a determination of the 

 crystal form but their shapes suggest that they may be orthorhombic 

 or tetragonal. However, E. S. Larsen determined it to be isotropic 



13 Frank L. Hess and Roger C. Wells. Journ. Franklin Inst. Philadelphia, vol. 189, pp. 225-237, February, 

 1920. 



