HTDROU8 SILICATES — MARGAROPHYLLITE SECTION. 305 



Indurated Talc, is a slaty talc, of compact texture, and 

 above the usual hardness, owing to impurities. 



Rensselaer ite. A compact cry p to-crystalline rock, from 

 St. Lawrence and Jefferson counties. IS 7 . Y., of white, yellow, 

 or grayish-white colors, and even black. It has sometimes 

 the form and cleavage of pyroxene, and is in part at least a 

 product of the alteration of that mineral. 



Composition. £H 2 %Mg 3 Si .= Silica 62-8, magnesia 33o, 

 water 3*7=100. It usually contains a little iron replacing 

 magnesium. 13. B. infusible. Moistened with cobalt nitrate 

 assumes a ]3ink tint. Not acted upon by hydrochloric acid. 

 In closed tube gives a little water, but not till highly 

 heated. 



Diff. The softness, unctuous feel, foliated structure, when 

 crystallized, and pearly lustre of talc are good characteris- 

 tics. It differs from mica also in being inelastic, although 

 flexible ; from chlorite, kaolinite, and serpentine in yielding 

 little water when heated in a glass tube. Only the massive 

 varieties resemble the last-mentioned species, and chlorite 

 has a dark olive-green color. Pyrophyllite, which cannot be 

 distinguished in some of its varieties from talc, becomes 

 dark blue when moistened Avith cobalt nitrate and ignited. 



Obs. Occurs in Cornwall, near Lizard Point ; at Portsoy 

 in Scotland ; at Croky Head, Ireland ; in the Greiner 

 Mountain, Saltzburg. Handsome foliated talc occurs at 

 Bridgewater, Yt. ; Smithfi Id, B. I. ; Dexter, Me. ; Lock- 

 wood, Newton and Sparta, N. J., and Amity, N. Y. On 

 Staten Island, near the Quarantine, both the common and 

 indurated are obtained ; at Cooptown, Md. , green, blue, 

 and rose-colored talc occur. Steatite or soapstone is abun- 

 dant, and is quarried at Grafton, Yt., and an adjacent 

 town ; at Francestown and Orford, N. H. It also occurs 

 at Keene and Bichmond, N. H. ; at Marlboro' and Ncav 

 Bane, Yt. ; at Middl held, Mass. ; in Loudon County, Ya., 

 and at many other places. 



Steatite may be saw r n into slabs and turned in a lathe. It 

 is used for firestones in furnaces and stoves, and fire-places. 

 It receives a polish after being heated, and has then a deep 

 olive-green color. The finer kinds are made into images in 

 China, and into inkstands and other forms in other coun- 

 tries. Potstone is worked into vessels for culinary pur- 

 poses in Lombardy. The harder kinds are cut into gas jets. 

 Steatite is also used in the manufacture of porcelain • it 



