Cross and Ililhhnnn/ .]/;„.,-<>/* n<»» Pih-r* Peak. 2-Sl 



Art. XXXIII.— Communications from the U. S. Geological 

 Survey, Rocky Mountain Division. II. Notes on some inter- 

 tsling Minerals occurring near Pike's Peak, Colorado; by 

 Whitman Cross and W. F. Hillebrand. 



The region about Pike's Peak, in El Paso County, Colorado, 



has, within the prist few years, become well known to mineral- 

 ogists the world over through the large and perfect crystals of 

 Amazon stone (microcline), which have found their way into 

 almost every collection of importance, in Europe as well as in 

 America. Other minerals, for the most part associated with 

 the Amazon stone in occurrence, have also come into circula- 

 tion to a less extent. The following minerals have been 

 announced from this region, and are all authentic, viz : micro- 

 cline, albite, biotite, quartz (smoky and clear), fluorite, colum- 

 bite, gothite, hematite and limonite (pseudomorph after 

 siderite), arfvedsonin . astro] In llite and zircon. 



With but one or two exceptions the minerals named occur 

 in "cavities" or "pockets" in granite, and although large 

 quantities of some of the species have been found there is 

 scarcely a mineral locality which at first sight seems more 

 unpromising than this. The coarse reddish granite of the dis- 

 trict disintegrates rapidly through the action of the weather 

 into a coarse, gravel-like mass, and many of the mountain 

 slopes are made of such material, lying at a very steep angle, 

 with solid rock projecting through it here and there. On find- 

 ing fragments oi crystals in the debris, the prospector for 

 th pick and shovel in hand, endeavors to find the 

 original cavity from which the fragments came. The "cavi- 

 ties " are very irregular in shape and size, and yield varying 

 quantities of crystals. A single cavity has been known to 

 yield more than a ton of crystallized specimens. All so far 

 discovered have been on the surface. That a direct connec- 

 tion exists between the tendency of the granite tod 

 so readily, the formation of the cavities, and the deposition of 

 these various minerals in them, can hardly be doubted. 



region, have come to our notice, and are thought worthy of 

 description. Wo can add to the above list of minerals, topaz. 

 phenifcite, cryolite, thomsenolite, and others not yet fully 

 determined. 



The phenacite and topaz were found about two years ago by 

 Thebaut, a prospector of Colorado Springs, associated 



n. xueoaui, a pros 

 r ith feldspar, smoky quartz and 

 escribed. A crystal of phemi 

 *ev. R. T. Cross, "of West Deny 



