CONSTITUENT MINERALS OF ROCKS. 61 



in granular limestone. Color, pale yellow and brownish yellow. Brittle, without 

 cleavage or much lustre. Hardness, as with chrysolite. G. = 3.1-3.24. Com- 

 position : nearly like chrysolite, but containing fluorine: Silica, 33, magnesia, 56, 

 protoxyd of iron, 3, fluorine, 8. 



3. Protoxyd-Silicates containing water. 



66. (17.) Talc. — In foliated masses; folia flexible, but not elastic; 

 also compact-massive, very soft, and having a greasy feel, either 

 granular, or very compact without any appearance of grains, when 

 it is called soapstone or steatite. Gr. = 2.5-2.8. Before the blowpipe, 

 infusible. Composition : a silicate of magnesia ; Silica, 62.12, mag- 

 nesia, 32.94, water, 4.94. 



(18.) Serpentine. — Usually massive, without cleavage or any gra- 

 nular texture, and soft enough to be scratched easily by a knife. 

 Sometimes thin-foliated, with the folia brittle ; also delicately fibrous, 

 and then often called amianthus and chrysotile. Sometimes in rectan- 

 gular and rhombic prisms. Color, dark to light green. Before the 

 blowpipe, fuses with difficulty on thin edges. Gr. = 2.2-2.6. Com- 

 position: Silica, 43.6, magnesia, 43.4, water, 13.0. 



(19.) Chlorite. — Thin micaceous, like mica, but folia not elastic, 

 and color olive-green, rarely whitish. Commonly massive, with a 

 fine granular texture, and of massive varieties. Quite soft, so as to 

 be cut easily with a knife. G. = 2.7-3. Before the blowpipe, 

 more or less fusible. Composition: Silica, 27.2, alumina, 23.1, 

 magnesia, 13.5, protoxyd of iron, 24.2, water, 12.1. This mineral 

 contains alumina, like those of the following subdivision ; but its 

 magnesia gives it its character, and it is usually associated with 

 other magnesian rocks. 



Clinochlore and ripidolite are names of other chlorites. (See author's Mine- 

 ralogy.) 



4. Alumina-Silicates containing water. 



67. (20.) Agalmatolite. — A compact material, resembling steatite, without 

 any distinct grain, white or grayish in color, and easily cut with a knife. It is one 

 of the kinds of materials cut into images in China. Specific gravity, 2.7-2.9. 

 It is a silicate of alumina and potash, containing about 46 per cent, of silica, 32 

 of alumina, 8 of potash, and 7 per cent, of water, with traces of some other in- 

 gredients. The Parojohite of Hunt is a rock of similar composition, from Canada; 

 and the dysyntribite of Shepard is a related compound, from northern New 

 York, of grayish green, brownish, and other shades of color. In the vicinity 

 of the dysyntribite large hexagonal crystals have been found, resembling the 

 Gieseckite of Greenland, and showing that gieseckite also belongs here, as ascer- 

 tained by G. J. Brush. These crystals, and also the gieseckite, are supposed 

 to be altered nepheline. 



