THE MINERALS OF IDAHO 345 



about a mile north of Junction Peak shows similar and more perfect 

 prisms of staurolite of the same size. 



Specimens from J/£ mile northwest of Bathtub Mountain contain 

 numerous small cruciform twins of brown staurolite up to 1 cm. in 

 size associated with small pink garnets and scattered large mica 

 pseudomorphs after cyanite. Similar specimens have been collected 

 from the summit of Bathtub Mountain. 



All of the specimens seen were collected from weathered surfaces. 

 From their nature it is evident that this area is capable of furnishing 

 numerous excellent mineralogical specimens of this mineral. 



THE ZEOLITE GROUP 



The minerals known collectively as the zeolites form a group of 

 hydrated aluminous silicates, principally of lime and soda with 

 sometimes potash, barium, or magnesia. They are all related in 

 composition and are similar in occurrence, but they differ widely in 

 crystallization. 



These minerals have long been regarded as the result of alteration 

 or weathering of basic igneous rocks, an idea that has now largely 

 been abandoned. They characteristically occur as vesicle fillings in 

 extrusive igneous rocks or occupying veins, either in or near igneous 

 intrusives and are probably deposited shortly following consolidation 

 of the igneous rock as a product from the heated water given off on 

 crystallization of the magma. 



The occurrence of such minerals is probably more widespread than 

 the following descriptions of Idaho specimens would indicate as they 

 are not of such a character as to excite the curiosity of the prospector. 

 Such few specimens as have been examined, with the exception of the 

 Challis material, have been more or less chance rock specimens. The 

 material for investigation has been unsufficient in most cases. The 

 crystallography of the minerals is difficult, due to the imperfections 

 of the crystals and the tendency to form complex groups and twins. 

 Furthermore, in some species of the group the optical properties are 

 subject to variation with variation in chemical composition not 

 thoroughly understood and are further complicated by anomalies 

 due to internal twinned structure, etc. In very few minerals of the 

 group do the optical structure and the external crystallographic 

 symmetry agree. 



In the following descriptions the minerals which have been available 

 are described as fully as the material at hand will permit. Many 

 points remain unsettled and the localities should furnish material for 

 additional investigation. 



Several reported occurrences of zeolites in Idaho are unmentioned 

 because no specimens have been available. A few years ago A. Albee 

 wrote from Salmon asking whether the Smithsonian Institution would 



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