MATERIALS FOR GLASS AND POTTERY. 375 



of the outcrops, with some stripping in places, will reveal much more than is 

 generally believed to exist. The most favorable district for explorations is in 

 the district between House and Smoothing Iron Mountains and the King 

 Mountains, and west of that area in Llano and Mason counties, but the 

 chances are very good further eastward and southward in Llano, Gillespie, 

 and Blanco counties. Northward in Llano and Burnet counties there may 

 also be other occurrences in accessible situations. We are speaking now of 

 talc and steatite, not of the various clays and other deposits which are often 

 popularly but incorrectly termed "soapstone." 



2. ASBESTOS AND ALLIED SILICATES. 



It is very commonly believed by residents of this region that asbestos 

 occurs in masses of workable extent. I have not yet observed an instance of 

 this, nor do I know of any occurrence of the mineral, unless it be in Blanco 

 or Gillespie counties, beyond the limits of my observations to date. In pri- 

 vate collections there are numerous specimens of so-called "asbestos," the 

 principal part of which are very fine examples of fibrous aragonite, a min- 

 eral of entirely different composition. Asbestos is an anhydrous magnesia- 

 lime silicate, a variety of Amphibole, allied to hornblende and tremolite, 

 while aragonite is a carbonate of lime, differing from calcite only in being 

 harder and heavier. 



Asbestos is tough and unaffected by heat or acids; aragonite whitens and 

 falls to pieces when strongly burned, and is rapidly dissolved by acid, with 

 brisk effervesence. 



Another mineral, occasionally found in small quantity in the rock of this 

 region, has sometimes been reported as asbestos. This is tremolite, which is 

 near asbestos in composition, being a white variety of amphibole. It is not 

 fibrous like asbestos, but occurs in thin-bladed crystals. Other specimens, 

 labelled asbestos in some collections, is fibrolite, a tough, semi-fibrous white 

 rock usually accompanying the garnet of the Burnetan exposures. 



VIII. MATERIALS FOR GLASS AND POTTERY. 



In the white sandstones of Castle Rock and Rock Fort, and the great areas 

 covered by the waste of the same beds in Llano County, especially along the 

 sources of Willow Creek and Phillips Creek, there is every probability that 

 excellent material exists for the manufacture of glass. No tests have yet 

 been made, but the sand is remarkably pure and in enormous quantity. 



Pottery clays are not abundant, probably, although there are places in 

 many of the creeks where very fine clays have been deposited, and in parts of 

 the Burnetan exposures there are good occurrences of albite. A sample of 

 this mineral from Clear Creek, Burnet County, contains only 1.09 per cent 



