THE MINERALS OF IDAHO 283 



WOLLASTONITE (320) 



Calcium metasilicate, CaO.SiOa. Monoclinic. 



Wollastonite is a mineral which frequently develops in limestone 

 by contact metamorphism adjacent to intrusive igneous masses. 

 It is usually white in color with a more or less pearly luster and 

 granular to fibrous structure. The granular varieties often resemble 

 white marble and fibrous forms frequently simulate tremolite in 

 appearance. The following localities have been noted in Idaho. 



ADAMS COUNTY 



Wollastonite has been listed with a question (?) by Livingston 

 and Laney 97 as occurring in limestone with other metamorphic 

 silicates in the contact copper deposits of the Seven Devils district. 



BLAINE COUNTY 



Specimens from the Starlight mine in Elkhorn Gulch near Ketchum, 

 in the Warm Springs district, contain white fibrous wollastonite 

 making up a lime-silicate rock with garnet and sahlite. Under 

 the microscope the wollastonite is fibrous with prismatic cleavage 

 parallel to the length, parallel extinction and rather high birefringence. 

 It is biaxial negative with 2V medium, /3 about 1.628. The axial 

 plane is across the fibers, so that the elongation is Y. Brilliant 

 black sphalerite is intimately intergrown with the wollastonite, 

 some of the prismatic grains of wollastonite being completely isolated 

 in the sphalerite. 



West of Hailey wollastonite occurs with diopside in metamorphosed 

 limestone near the large granite instrusion. 98 



In the Drummond claim, on Little Wood River, Muldoon dis- 

 trict, the ore occurs in a zone of contact metamorphism in which 

 wollastonite and less garnet, diopside, and epidote have been de- 

 veloped in a calcareous rock. 99 A specimen from this mine consists 

 of about equal parts of pale brown garnet and dense fibrous silky- 

 lustered white wollastonite, which is fibrous, biaxial negative opti- 

 cally with 2V large and refractive index 1.620 ±.002. 



CUSTER COUNTY 



A specimen from the Basin prospect north of the Trail Creek- 

 Lost River Pass consists of pinkish fibrous sheets of wollastonite 

 up to 4 mm. thick, in garnet-epidote rock. Under the microscope 

 the wollastonite is biaxial and negative with 2V small. The fibers 

 give parallel extinction with the optic axial plane across the length. 

 The refractive index, is 1.62. It is decomposed at boiling by 1:1 

 hydrochloric acid. 



97 D. C. Livingston and F. B. Laney. Idaho Bur. Mines and Geol., Bull. 1, p. C2, 1920. 

 " Waldemar Lindgren. U. S. Geol. Survey, 20th. Ann. Rept., pt. 3, p. 195, 1900. 

 »« J. B. Umpleby. U. S. Oeol. Survey, Prof. Paper 97, p. 109, 1917. 



