294 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



LATAH COUNTY 



Beryl is found in the pegmatites of the mica mines near Avon 

 associated with feldspar, quartz, mica, etc. The mineral has been 

 especially mentioned from the Levi Anderson and Muscovite mines, 14 

 and probably occurs in others. Specimens from this locality show 

 prismatic crystals up to 5 cm. in diameter and 15 cm. long. These 

 have fairly smooth prismatic planes but the terminations are in- 

 complete. In color they are all pale yellow-green and they vary 

 from translucent to transparent. Some small fragments might be 

 cut into pale colored gems. Often the crystals are greatly fractured 

 and many of them are iron stained. 



NEZ PERCE COUNTY 



Ernest Schernikow of New York has reported the finding of two 

 good blue beryl crystals near Lewiston. These were obtained from 

 an Indian squaw who would not reveal their source. 15 



THE GARNET GROUP 



The garnet includes a number of well-defined minerals crystalliz- 

 ing in the isometric system and having the general formula : 



3R"O.R'" 2 03.3Si02 



These vary by replacement of both the bivalent and trivalent 

 oxides, thus R"0 may be FeO, CaO, MgO, or MnO and R'" 2 3 may 

 be A1,0 3 , Fe,0 3 , or Cr 2 3 . The end members of the group which are 

 important in Idaho occurrences are: 



Almandite 3FeO.Al 2 3 .3Si0 2 



Spessartite 3MnO.Al 2 3 .3Si0 2 



Grossularite 3CaO.Al 2 3 .3Si0 2 



Andradite 3CaO.Fe 2 3 .3Si0 2 



The magnesium garnet, which has not thus far been demonstrated 

 to be the major constituent of any Idaho garnet, has the formula: 



Pyrope 3MgO.Al 2 3 .3Si0 2 



Members of the group containing titanium, chromium, etc., are 

 known but have not been reported from this State. While the ulti- 

 mate classification of any garnet demands an analysis, it is possible, 

 granting certain assumptions, to classify garnets for the purpose of 

 description here by their general properties and mode of occur- 

 rence. There seem to be limits to the miscibility of the several 

 members. From available data it seems that, so far as Idaho garnets 

 are concerned (1) to pink to red or purplish garnets in pegmatite are 

 variable isomorphous mixtures of almandite and spessartite; (2) red 



» Douglas B. Sterrett. Mica deposits of the United States, U. S. Geol. Survey Bull. 740, pp. 89-93, 1923. 

 " U. S. Geol. Survey. Mineral Resources of United States for 1907, p. 799. 



