4 SMITHSONIAN INSTITUTION 



The yield included a number of unusual arsenate minerals, some 

 very rare, others well crystallized, and groups of scorodite, an arsenate 

 of iron — the finest, I believe, yet to have been found. There were 

 also specimens of fluorite of various colors, some clear and flawless 

 and suitable for optical purposes, and others of a fine wine-red color 

 suitable for gems. 



From Ojuela, I attempted to reach by automobile the Sierra de 

 Banderas, where large sulfur deposits are known to exist. The road 

 led over a "barreal," or mud plain, and since this was the season 

 when one could expect sudden and violent storms, we proceeded with 

 one eye on the sky. When we were within sight of our objective, 

 a tremendous storm broke. The deluge, fortunately, caught us on 

 a small gravelly knoll, where we spent the night. The surrounding 

 terrain was converted into a sea of soft, tenacious mud, and we spent 

 almost the entire next day in returning to the main road 12 miles away. 



Another prolific locality was Cerro Mercado, the famous iron 

 mountain and Mexico's chief source of iron ore, just outside the 

 city of Durango. Here huge banks of high-grade iron ore are mined 

 by open quarry methods. These quarries are famous for their fine 

 clear yellow apatite crystals, which are found in scattered pockets, 

 in the mineable material, and I was fortunate in arriving at a time 

 when these crystals were being obtained in unusual size as well as 

 numbers. Many of these crystals are clear and flawless, of a sparkling 

 yellow color, and are suitable for gem cutting. 



A visit was made to Guanajuato, primarily to inspect the mineral 

 collection of the late Don Ponciano Aguilar. Guanajuato is the center 

 of an important mining area and has been the greatest producer of 

 silver in the world. The rich ores consisted of beautifully crystallized 

 silver minerals — argentite, pyrargyrite, polybasite, and others — but 

 desirable museum specimens are now available for purchase only in 

 an occasional old collection. 



The mineral deposits of Mexico have received comparatively little 

 attention from mineralogists, and precise information of the character 

 of the ores from even some of the most prolific mining districts is 

 very meager. Field work by the Smithsonian Institution, carried on 

 intermittently since 1926, has resulted in the accumulation of the 

 greatest collection of Mexican ores and minerals extant. During 

 the 15 years this survey has been in progress, important mining dis- 

 tricts have become exhausted and the minerals and ores are, even 

 now, no longer obtainable. This material will be made the basis of 

 two reports, one on the ore deposits and another on the minerals of 

 Mexico. 



