DISTRIBUTION AND FREQUENCY OF THE TOPAZ 189 



ance of the very fine grained tuff. It may also be noted that of the four 

 or more possible pyramids, as well as of the domes and basal pinacoid, 

 the pyramid (221) was the only one capable of strong development, even 

 under the most favorable conditions. 



Distribution and frequency of the topaz crystals. — As already stated, 

 the topaz crystals of the lithophysal cavities are very fluctuating in 

 amount. Where the lithoph3'sa3 are characteristically developed the crys- 

 tals are very abundant. This is more apt to be the case where the rock 

 is of a very light gray or nearly white color. But true lithophysae pass 

 by insensible gradations into irregular cavities that show but little if 

 any development of concentric shells. These cavities also may contain 

 topaz crystals, but are not so apt to do so. In such portions of the 

 rhyolite one will have to hunt carefully for the topazes ; but it often hap- 

 pens that where the cavities are scarce or where they contain but few 

 topaz crystals, the opaque crystals are very much in evidence. For in- 

 stance, over limited areas of the exposed rhyolite one may see at times 

 one opaque topaz crystal or cluster to every square foot of surface. At 

 other times and places onl}' an occasional crystal may be seen. In one 

 particular instance the writer extracted from about four cubic feet of 

 rotted or partially disintegrated rhyolite 336 crystals and clusters. These 

 crystals were in many cases distinctly transparent or partially so, but 

 many of them Avere transitional to the opaque variety. Most of them 

 were of very fair size, being three-quarters of an inch to one and one-half 

 inches in size. The total weight of these 336 crystals was 24 ounces. 

 These crystals were undoubtedly in place. The opaque variety has prol> 

 ably a much wider distribution than has the transparent crystals. In a 

 letter from Mr Maynard Bixl)}', of Salt Lake City, to whom the writer 

 is indebted for many courtesies and for much valuable information as to 

 this topaz locality, it is stated that these opaque topazes occur "all 

 through the belt of rhyolite" and are well developed at a locality where 

 the mineral bixbyite was first found, some 20 miles northerly from Topaz 

 mountain. 



SPECULAR HEMATITE 



The occurrence of specular hematite, usually in the form of thin 

 flakes, in cavities of rhyolite and of other acid igneous rocks is a very 

 common feature in the Cordilleran west, but its occurrence in plainly 

 developed lithophysse has not, so far as the writer is aware, been noted 

 heretofore. It is, however, very universally present in the lithoph3'sae of 

 Topaz mountain, attached to the topaz and to the quartz crystals. Its 



