THE MINERALS OF IDAHO 297 



of refraction of the garnet is 1.815. A clear transparent brownish- 

 red irregular fragment from this lot has an index of 1.813. A clear 

 brown-red trapezohedral crystal 5 mm. in diameter gives purplish 

 fragments with brown stained grains. The index is 1.815. A clear 

 transparent brownish-red flake has an index of 1.815 while a clear 

 purplish-red fragment of the same size has an index of 1.804. A fine 

 transparent brown-red piece 1 cm. in diameter has an index of 1.807 

 and upon testing gave a strong manganese reaction. A black well- 

 formed trapezohedral crystal 7 mm. in diameter, opaque in the 

 specimen, when crushed was found to be stained along cracks and 

 the garnet was colorless except in the thickest pieces, which were 

 rose red. This has an index of 1.818. It is thus evident that, in 

 this lot at least, the color of the garnet is of no value in classification 

 nor can the spessartite-bearing garnets be determined by their 

 refractive index. 



Placer concentrates from the Rich Hill Mining Co. and others 

 marked Rhodes Creek contain purplish-red garnet. 



ELMORE COUNTY 



Purplish-red garnet is abundant in sand concentrates from the 

 Big Rock placer claim, Wood Creek, Elmore County. 



IDAHO COUNTY 



Placer concentrates from the various localities in the Elk City 

 district contain moderate amounts of garnet, mainly brown-red in 

 color. 



LATAH COUNTY 



Pink garnets are of frequent occurrence in the pegmatites which 

 are mined for mica near Avon in Latah County. A specimen from 

 the Luella mica mine has been examined in detail. 17 This specimen, 

 which was collected by Dean Francis A. Thompson, of Idaho School 

 of Mines, is stated to be typical of the garnet occurring in the mica- 

 bearing pegmatite of that area. The pegmatite consists of coarse 

 crystals of muscovite, quartz, feldspar, and abundant black tourma- 

 line in addition to the garnet. The garnet is purplish rose-red in 

 color and is much traversed by cracks which render it friable, granu- 

 lar, and somewhat opaque. It forms grains or imperfect trapezo- 

 hedral crystals up to 1 cm. in diameter embedded in quartz or in 

 mica, the most perfect crystals being those which are surrounded by 

 muscovite. There is no flattening of the garnet crystals between 

 the laminae of mica. 



A sample carefully selected and purified by the use of an electro- 

 magnet and heavy solutions was analyzed yielding the results and 

 ratios below: 



i' Earl V. Shannon. Note on garnet from a pegmatite in Idaho. American Mineralogist, vol. 7, pp. 171- 

 172, 1922. 



