JPart II. 



THE ROCKS. 



A.— SOAP-STONE. 



This, although not properly a building stone, is of sufficient economic 

 importance to merit attention. 



(1) COMPOSITION AND USES. 



Pure soap-stone is a massive or schistose variety of the mineral talc. 

 In this form it is often called steatite, soap-stone, or pot-stone; chemi- 

 cally, then, it is a hydrous silicate of magnesia of the following compo- 

 sition, according to Dana:* Silica, 62.8; magnesia, 33.5; water, 3.7. 

 The mercantile varieties are, however, nearly always more or less im- 

 pure, iron sometimes replacing a part of the magnesia, while antho- 

 phyllite, pyrite. pyrrohotite and quartz are common accessories. It is 

 soft enough to be easily scratched by the thumb-nail, and has a marked 

 soapy or greasy feeling, two characteristics which readily distinguish it 

 from most other rocks. It can be sawn into slabs or turned on a lathe, 

 and being, when well seasoned, very refractory, is miich used for fire- 

 stones in furnaces and stoves; it is also very extensively used for lining 

 stationary wash-tubs. The finer varieties are, according to Daua, made 

 into images in China, and into ink-stands and similar articles in other 

 countries. It is cut into vessels for culinary purposes in Lombardy, and 

 was so used to some extent by the aborigines of North America. The 

 harder varieties are cut into gas jets, and it is also used in the manu- 

 facture of porcelain. " French chalk n is a fine, compact variety used 

 for tracing on cloth and for removing grease spots. The waste frag- 

 ments are sometimes ground up and used for lubricating machinery. 

 It is also utilized to some extent in the manufacture of so-called mineral 

 paints. The total product of the United States for 1882 has been esti- 

 mated at about 6,000 tons, with an average valuation of $15 per ton.t 



* Manual of Mineralogy and Lithology, p. 305. 



t Mineral Resources of the United States, 1883, p. 464. 



357 



