THE MINERALS OF IDAHO 287 



prismatic cleavages. The extinction is parallel, the elongation 

 positive, and the crystals tend to lie on a face giving medium low 

 birefringence and showing the emergence of a negative bisectrix, 

 probably obtuse but looking like an acute bisectrix with 2V large. 

 The refractive indices are a = 1.612, |8 == 1.621, 7 = 1.635, birefringence 

 = 0.023. 



The second material associated with the preceding and apparently 

 •derived from it by alteration or shearing is made up of very fine 

 fibers in matted aggregates having, in a section, a variable and non- 

 pleochroic pale greenish-brown color and about the same birefringence 

 as the other. The extinction is parallel and the elongation positive. 

 The refractive indices are variable with a = about 1.595. The 

 granular material of this specimen consists of glassy white to pinkish 

 grains of the first mineral described above having scattered grains 

 of actinolite which is identified by its green pleochroic color, negative 

 optical character and extinction inclined about 17°. 



The second specimen from the lot labeled as from Orofino con- 

 sists of a large splintery fibrous mass 40 cm. in length and having a 

 dirty white color. Under the microscope this is made up of coarse 

 blades tending to split into minute fibers of positive elongation and 

 parallel extinction. The indices of refraction are approximately 

 « = 1.608, 7 = 1.630, birefringence 0.022. 



Apparently all of the preceding are anth.ophyllit.es, varying in 

 refractive indices probably with variation in iron and possibly water 

 content. The finely fibrous forms are apparently secondary and 

 derived by some mechanical process of weathering or shearing from 

 a much coarser form of the same mineral. No indication of the 

 source or origin of the anthophyllite is furnished by the specimens 

 examined. 



SHOSHONE COUNTY 



The anthophyllite found by Ransome 4 in the Hercules mine 

 is the high iron variety described below under the name ferroan- 

 thophvllite. 



FERROANTHOPHYLLITE 

 Iron silicate, FeO.Si0 2 . Orthorhombic. 



The name ferroanthophyllite has been suggested for a member 

 of the anthophyllite group in which the essential magnesia is wholly 

 or largely replaced by ferrous iron. 5 Specimens from Idaho have 

 been described in detail. Similar iron anthophyllite had previously 

 been described from Massachusetts and several Scandinavian 

 localities. 



* F. L. Ransome. U. S. Oeol. Survey, Prof. Paper 62, p. 99, 1908. 



« Earl V. Shannon. Description of ferroanthophyllite, an orthorhombic iron amphibole from [daho 

 •with a note on the nomenclature of the anthophyllite group. Proc. U. S. Nat. Museum, vol. 59, pp. 

 397-401, 1921. 



