THE MINERALS OF IDAHO 307 



Alberta tunnel, consists of very fine dense flinty brown massive 

 garnet with waxy luster. A specimen from a fissure zone in No. 8 

 crosscut. Alberta tunnel, consists of pale olive green to yellow masses 

 of garnet showing an occasional crystal face. Another from the 

 second east drift, No. 300 level, Empire mine, is dense very fine- 

 grained greenish garnet containing some disseminated fine grains of 

 chalcopyrite and bornite. A typical specimen from the dump of 

 the north tunnel is a very heavy dense fine-grained pale-greenish 

 rock with greasy luster which is apparently pure garnet. A second 

 specimen from the dump of this tunnel contains abundant small 

 well-formed greenish yellow garnet crystals showing equal develop- 

 ment of dodecahedron and trapezohedron, in fluorite. A third 

 specimen, typical ore, from bins at the North tunnel contains vitre- 

 ous brown grains and crystals of garnet in a matrix of chalcopyrite. 

 Two specimens labeled "Copper bullion" show in one specimen 

 small brown crystals and granules of garnet with magnetite and 

 calcite in coarse white calcite, while the other specimen consists of 

 yellow-brown porous masses of garnet with large imperfect magnetite 

 crystals. Some fine little olive-green garnet crystals showing 

 dodecahedron modified by trapezohedron abut against calcite 

 filling cavities. 



LEMHI COUNTY 



A little garnet has been noted in association with forsterite in 

 metamorphosed limestone on the Colorado group claims in the 

 Spring Mountain district. 28 The Bruce Estate in the same district 

 is said to have opened a copper-bearing contact zone in limestone 

 which probably contains garnet, although no specimens of garnet 

 rock have been seen from this mine. 



FORSTERITE (375) 

 MAGNESIA OLIVINE 



Magnesium silicate, 2MgO.Si0 2 . Orthorhombic. 



Forsterite has been reported from 4 localities in Idaho, three of 

 them contact-metamorphic products in limestone and the third an 

 original constituent in an igneous rock. 



ADAMS COUNTY 



Forsterite has been listed with a question (?) as occurring as a 

 contact mineral in the contact-metamorphic ore deposits of the 

 Seven Devils district. 29 



2' J. B. Umpleby. U. S. Oeol. Survey, Bull. 528, p. 88, 1913. 



" D. C. Livingston and F. B. Laney. Idaho Bur. Mines and Qeol. Bull. 1, p. 62, 1920. 



