THE MINERALS OF IDAHO 329 



in one case, a face giving the indices (10.0.1). The epidotes are 

 minute, rarely over 2 mm. long and are limpid transparent yellow- 

 green in color. 



LEMHI COUNTY 



In Lemhi County epidote is often strikingly developed in the re- 

 crystallized sedimentary rocks and also occurs as a contact mineral 

 in the Mayflower group of claims in the Mackinaw district. The 

 deposits here consist of quartz replacements along a brecciated zone 

 in siliceous schist. The brecciated material is locally almost en- 

 tirely made up of garnet with associated epidote and magnetite. 54 

 At the Carmen Creek mine in the Carmen Creek district the ore 

 occurs as lenses of quartz distributed through a band of schist 8 to 

 15 feet wide, the quartz totaling about one-third of the width. 

 Much of the schist itself is mineralized. In addition to the metallic 

 minerals actinolite and magnetite are widely developed; green epidote 

 is less common. Magnetite occurs in the vein quartz but the actino- 

 lite and epidote are confined to the adjacent schist. 55 



OWYHEE COUNTY 



Epidote is of common occurrence in places in the Silver City dis- 

 trict where it replaces basalt or some other igneous rock adjacent 

 to the silver veins. It is for the most part massive with aphanitic 

 appearance and the usual yellow green or pistachio green color. A 

 specimen from a raise 1,300 feet from the portal of the Blaine tunnel 

 shows this fine grained epidote replacing basalt adjacent to the 

 silver vein. A number of specimens from the dump of a tunnel on 

 the south side of Long Gulch below the Blaine tunnel contain epidote. 

 In the first of these small yellow-green epidote crystals replace frag- 

 ments of altered rock inclosed in the quartz-adularia vein. In 

 another, massive epidote haloes surround fragments of the igneous 

 rock included in the vein and, in the third, a breccia of basalt frag- 

 ments is cemented by quartz and massive yellow-green epidote, the 

 latter in masses up to 2 by 6 cm. in size. 



No epidote has been seen from the contact-metamorphic ore- 

 bodies of the South Mountain district. 



SHOSHONE COUNTY 



Epidote occurs as dull-green aphanitic veins and surfaces of im- 

 perfect curved opaque greenish-yellow crystals lining fractures in an 

 altered basic dike on the Corby claim on Pine Creek. 



PREHNITE (411) 



Calcium aluminium silicate, Orthorhombic. 



H 2 0.2CaO.Al 2 3 .3Si0 2 . 



Prehnite has been found in Idaho in two contact metamorphic 

 deposits in Custer County, associated with garnet and epidote, etc. 



«« J. B. Umpleby. U. S. Geol. Survey, Bull. 528, p. 155, 1913. 

 s» J. B. Umpleby. U. S. Geol. Survey, Bull. 528, p. 127, 1913. 



