HYDROUS SILICATES—MARGAROPHYLLITE SECTION. 305 
Indurated Taic, is a slaty tale, of compact texture, and 
above the usual hardness, owing to impurities. 
Rensselaerite. A compact erypto-crystalline rock,.from 
St. Lawrence and Jefferson counties, N. 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, 4Mg O,Si=Silica 62:8, magnesia 335, 
water 3°/=100. al usually contains a little iron replacing 
magnesium. B.B. infusible. Moistened with cobalt nitrate 
assumes a pink 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 tale 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 tale, becomes 
dark blue when moistened with cobalt nitrate and ignited. 
Qos. Occurs in Cornwall, near Lizard Point ; at Portsoy 
in Scotland; at Croky Head, Ireland; in the Greiner 
Mountain, Saltzbure. Handsome foliated talc occurs at 
Bridgewater, Veta Smithfi Id, It. I. ; Dexter, Me.; Lock- 
wood, Newton and Sparta, N. J, and, Amity: NL Ys Om 
Staten Island, near the Quarantine, both the common and 
indurated are obtained ; at Cooptown, Md., green, blue, 
and rose-colored tale occur. Sfeatite or soapstone is abun- 
dant, and is quarried at Grafton, Vt:, and an adjacent 
town; at Francestown and Orford, N. H. It also occurs 
at Keene and Richmond, N. H.; at Marlboro’ and New 
Fane, Vt. ; at Middl field, Mass. ; in Loudon es Vas 
and at many other places. 
Steatite may be sawn 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- 
posesin Lombardy. ‘The harder kinds are cut into gas Jets. 
Steatite is alsoused in the manufacture of porcelain ; it 
