THE MINERALS OF IDAHO 417 



many thousands of feet of subsequent strata have overlain or suc- 

 ceeded them. The deposits are more properly analogous to coal and 

 limestone and to the Clinton iron ores of the Appalachian region 

 than they are to ore deposits such as veins or lodes or to alluvial 

 deposits of the placer type. 



Thin sections of the richest oolitic ore show under the microscope 

 that the rock consists mainly of ovules or concretions of a crypto- 

 crystalline substance which, in some concretions, is surrounded by 

 banded zones of crystalline fibers with local isotropic bands, all 

 having the same average index of refraction (about 1.60) and ap- 

 parently representing the phosphatic substance. In some places 

 the interstices are filled with calcite and in others with an isotropic 

 material which appeal's to be identical with the cores of the concre- 

 tions. The fibrous material has parallel extinction. The isotropic 

 substance is probably collophanite and the doubly refracting sub- 

 stance may be called quercylite which, however, is not a definite 

 mineral, but a mixture of different members of the series of lime 

 phosphate minerals. 23 



In some specimens the black phosphate rock is cut by thin seams 

 of gypsum and rather frequently it is coated along cracks with 

 purple fluorite. 



Two specimens have been examined carefully by the writer dur- 

 ing the course of this work and these were probably typical of the 

 coarse and fine types of the material. The first of these was col- 

 lected by G. R. Mansfield and the locality is given as on the west 

 side of the Teton Basin in southeastern Idaho. This is conglomeratic 

 in texture and consists of vitreous black ellipsoidal pebbles or con- 

 cretions up to 5 mm. in diameter in a somewhat friable brownish 

 matrix. In thin section this rock is seen to be made up of rounded 

 masses of a material which is brown in transmitted light and in part 

 opaque from inclusions. Surrounding these masses is calcite which 

 penetrates them along fractures and replaces them to a slight extent. 

 The concretionary masses are either isotropic or show that feeble 

 aggregate birefringence characteristic of metacolloidal substances. 

 Occasional angular grains of clear quartz are included in the con- 

 cretions and small angular cavities within them have been lined 

 with a finely fibrous layer of chalcedonic structure, the fibers of 

 which have parallel extinction and positive elongation. The index 

 of both the isotropic and cryptocrystalline material is 1.613 ±0.003. 

 The isotropic material is doubtless collophanite while the birefring- 

 ent material may be called quercylite. The collophanite gave a 

 distinct fluorine reaction with potassium bisulphate. 



« Waldemar T. Schaller, quoted by R. W. Richards and G. R. Mansfield. U. S. Geol. Survey, Bull. 

 470, pp. 376-378. 



54347— 26t 28 



