710 TRANS-PECOS TEXAS. 



CHAPTER IV. 



MINERALS OF TRANS-PECOS TEXAS. 



The following is a list of those minerals and rocks of Trans-Pecos Texas 

 which up to this time could be classified by their appearance, blowpipe tests, 

 and laboratory work. This list is far from being complete, but it comprises 

 a number of the more important and valuable minerals, building stones, and 

 ores of West Texas, giving the localities where they are found. 



Owing to the frequent and excessive metamorphism, more time will be re- 

 quired to classify the large number of specimens on hand awaiting determi- 

 nation by careful microscopic and laboratory studies (which no doubt will' 

 lead to the determination of a number of new minerals) than could be spared 

 at present. 

 Quartz. 



Common Quartz, Milky Quartz, and Granular Quartz are found all 

 over the Quitman Mountains, the Carrizo, and the foothills of the Sierra 

 Diabolo. 



Mountain Crystal, Sagenitic Quartz (holding acicular crystals of other 

 minerals), Adventurine (with mica inclusions) in the Quitman Mountains, 

 particularly on the contacts between the granitic and porphyritic rocks 

 in the second range of these mountains. 



Flinty Quartz prevails in the Davis Mountains, though Smoky, Milky, 

 Granular Quartz, Agates, and Mountain Crystals are also found there. 



Agates. Banded, cloudy, and milky agates are found in any desired 

 quantities, loose and embedded in the rhyolitic material, between Marfa 

 and the Chinatti Mountains. Between Sierra St. Jago and the Rossillas 

 moss agates of great beauty and variety are are found. 



Onyx is found in streaks in the lava along the road from Marfa to the 

 Saocito ranch. 

 Amphibolite. 



Amphibolite is found in the northwestern part of the Sierra Blanca 

 group, but more sparsely in the northern part of the Quitman Mountains. 

 Hornblende. 



Hornblende is found in the northern part of the Quitman Mountains, 

 in the Sierra Carrizo, at the Rattlesnake tank, in a spur of the Van 

 Horn Mountains, and in the Sierra Blanca group and its northwestern 

 extension; Diorite, Syenite, Tremolite, Aphanite, and related rocks are 

 also found in these mountain ranges. 



