MINERALOGY. 433 



rouge and colored pastels ; also used as polishing powder. 

 The Romans called it Pumex (which has been corrupted 

 into pumice), and employed it for various toilet purposes. 

 In the present time it serves instead of oil to smooth the 

 wheels of machinery. Potstone, the Lapis ollaris of the an- 

 cients, found on the mountains of St. Bernard, St. Gothard? 

 etc.. bears much likeness to the foliated talc we have 

 just been describing. Various domestic utensils, stoves, 

 etc., are manufactured of potstone, which, being very 

 hard, almost equals iron in resisting igneous action. One 

 stove specimen, found in Germany, is celebrated as hav- 

 ing lasted one thousand years. 



Lapis Lazuli (Ultramarine) is of rich color, Berlin 

 or dark azure blue ; luster vitreous ; translucent on the 

 edges. Occurs in compact masses ; seldom as crystals. 

 When powdered it constitutes the most beautiful and 

 durable of blue paints, called ultramarine, and has been 

 one of the most costly colors. H. = 5 to 6 ; G. .= 2.8 

 to 2.4. Found in Siberia, Thibet, and China. Lapis 

 lazuli is rare ; highly esteemed for costly vases, and inlaid 

 work for ornamental furniture, it is also used in the 

 manufacture of mosaics, boxes, rings, etc. Magnificent 

 slabs of great value are contained in some of the Italian 

 cathedrals. The artificial ultramarine, being much 

 cheaper, has taken the place in the arts, entirely, of the 

 native lapis lazuli. 



Turquoise. Luster waxy, translucent on the edges ; 

 color blue, verging into green ; fracture conchoidal ; 

 shape, reniform or globular masses. Turquoise is 

 brought from Persia, and so highly valued as a gem that 

 small specimens of the pure and finely-tinted stones, 

 measuring but five or six lines, command a high price, 

 19 



