SILICA. 273 



Specific gravity from 2.50 to 3.00. Before the blowpipe, it becomes of a brownish red 

 colour, hardens, but melts only with great difficulty on the edges ; with borax, it fuses with 

 difficulty into a green glass, which becomes almost white on cooling. By calcination, it loses 

 water and becomes harder. It is partly attacked by acids. 



Varieties. Noble or Precious Serpentine. This includes the translucent specimens, and 

 has usually a green colour with a tint of yellow. It is harder than many other varieties, and 

 its fragments often have very sharp edges. 



Common Serpentine. It is of various shades of green, usually dark, and with brown or 

 black intermixed. The colours are seldom uniform, but are arranged in stripes, veins, clouds, 

 spots, etc. Its hardness is less than that of the precious serpentine, and its fracture is usually 

 dull. 



Nephrite. The colours are grey, green and white. It is massive, and in rolled pieces. 

 Dull or glimmering. Fracture splintery. Strongly translucent, and difficultly frangible. 

 Hardness 7.0. 



Steatite or Soapstone. Colour white, red and yellow ; often with markings of green, pur- 

 ple and black. Occurs massive, in crusts, and rarely in false crystals. Fracture splintery 

 and uneven. It is soft, sectile, and has a very greasy feel. Somewhat translucent on the 

 edges. Hardens before the blowpipe ; becomes black, but is infusible. 



Potstone. Has a greenish grey or leek-green colour ; is coarse, and indistinctly granular. 

 Its softness and tenacity are such that it can be readily turned on a lathe, and formed into 

 vessels of various kinds. It is perhaps nothing more than a variety of indurated talc. 



The Picrolite of Haussman, appears to be identical with serpentine. It is described as 

 being massive or fibrous, with a radiated structure. Colour leek-green, passing into yellow. 

 Translucent on the edges. Streak somewhat shining. Colours glass of borax green, but the 

 colour disappears on cooling. 



The Retinalite of Dr. Thomson, is probably also nothing more than a variety of serpentine. 



The beautiful marble called Verd antique, is white limestone, with grains and spots of 

 green serpentine. A notice of our principal localties of this valuable material will be found 

 in the article on Marble (page 67). It is sometimes treated of in connection with serpentine, 

 as it is to the presence of that mineral that the great beauty of this marble is to be ascribed. 



Composition. Precious Serpentine — Silica 41.95, magnesia 40.64, alumina 0.37, pro- 

 toxide of iron 2.22, water 11 .68, carbonic acid and bitumen 3.42 {Lychnell). 



Common Serpentine — Silica 42. 16, magnesia 42.26, protoxide of iron 1 .98, water 12.33, 

 carbonic acid and bitumen 1 . 03 {Lychnell). 



Soapstone, from Cornwall, Eng. — Silica 45 . 00, magnesia 24 . 75, alumina 9 . 25, potash 

 0.75, water 18.00, oxide of iron 1.00 (Klaproth). 



Potstone, from Sweden — Silica 49.01, magnesia 30.20, alumina 6.08, protoxide of iron 

 11.40, water 4.20 {Thomson). 



MiN. — Part II. 85 



