THE MINERALS OF IDAHO 299 



placers near Lewiston. 19 Garnets resembling spessartite and show- 

 ing rounded crystal faces were sent to Salt Lake for cutting from a 

 locality near Orofino in 1915. 20 



OWYHEE COUNTY 



A specimen of pegmatite from the Silver City mine, Silver City 

 district, contains scattered small purplish red trapezohedral garnets 

 in a coarse aggregate of mica and feldspar. These crystals are sharp 

 and perfect and average 3 mm. in diameter. They have an index of 

 refraction of 1.812. 



SHOSHONE COUNTY 



Small crystals of reddish garnet are fairly abundant in the contact- 

 metamorphic zones that surround the intrusive mass of monzonite 

 north of Canyon Creek in the Coeur d'Alene district. The mineral 

 occurs also as a gangue constituent intergrown with metallic sulphides 

 and magnetite in ore deposits within the metamorphic zones parti- 

 cularly the Helena-Frisco, Custer (Tamarack), Granite (Success) and 

 Sixteen-to-one (Rex) mines. In the last two properties some of the 

 crystals are large enough to be recognized by the naked eye but for the 

 most part the mineral is microscopic. In the Granite (success) 

 mine, for example, a pink tint which is characteristic of the quartzite 

 close to an orebody is seen in thin section to be due to the presence of 

 numerous microscopic garnets. 21 



South of the Coeur d'Alene district, in the Avery quadrangle, 

 especially along the St. Joe- Clearwater divide, garnet is extensively 

 developed in the metamorphosed Belt sediments where they approach 

 the central Idaho batholith. A number of specimens collected in 

 this area by F. C. Calkins and E. L. Jones, jr., of the United States 

 Geological Survey have been examined. A specimen labeled "gar- 

 netiferous quartzite" from Lookout Mountain, Avery quadrangle, 

 consists of sandy dirty white quartzite having micaceous parallel 

 parting planes from 5 mm. to 1 cm. apart. Rusty brownish red 

 garnets up to 3 mm. in diameter occur along these partings (10-C-36). 

 Three specimens labeled staurolite schist (ll-C-129, 130, 131) from 

 near bench mark 6225, Avery quadrangle (Bathtub Moimtain(?)) 

 are similar to each other. These consist of fine grained mica schist 

 containing abundant small garnets and staurolite crystals 5 mm. 

 long, some of them cruciform, and a few large coarsely granular mica 

 pseudomorphs, probably after cyanite. The garnets are flattened 

 parallel to the schistosity. They average 1-2 mm. in diameter and 

 arc purplish rose pink in color. The index of the garnet of one 

 specimen is 1.810 and of another 1.812. 



18 U. S. Geol. Survey, Mineral Resources for 1892, p. 708. 



20 U. S. Qeol. Survey, Mineral Resources for 1915, pt. 2, p. 851. 



J i F. L. Ransome and F. C. Calkins. U. S. Geol. Survey, Prof. Paper 62, p. 99, 1908. 



