250 DESCRIPTIONS OF MINERALS. 



calcium-iron amphibole. Glassy actinolite includes the bright 

 glassy crystals, of a rich green color, usually long and slen- 

 der, and penetrating the gangue like tremolite. Radiated 

 actinolite includes olive-green masses, consisting of aggre- 

 gations of coarse acicular fibres, radiating or divergent. 

 Asbestiform actinolite resembles the radiated, but the fibres 

 are more delicate. Massive actinolite consists of angular 

 grains instead of fibres. GL =3*0-3 '1. The name actino- 

 lite alludes to the radiated structure of some varieties, and 

 is derived from the Greek, aktin, a ray of the sun. 



Asbestus. In slender fibres easily separable, and some- 

 times like flax. Either green or white. Amianthus, in- 

 cludes fine silky varieties. (Much so called is serpentine ; 

 serpentine is hydrous, and is thereby easily distinguished.) 

 Ligniform asbestus is compact and hard ; it occurs of brown- 

 ish and yellowish colors, and looks somewhat like petrified 

 wood. Mountain leather occurs in thin, tough sheets, look- 

 ing and feeling a little like kid leather ; it consists of inter- 

 laced fibres of abestus, and forms thin seams between layers 

 or in fissures of rocks. Mountain cork is similar, but is in 

 thicker masses ; it has the elasticity of cork, and is usually 

 white or grayish white. 



The preceding light-colored varieties contain little or no 

 alumina or iron. 



Composition of glassy actinolite : Silica 59*75, magnesia 

 21*1, lime 14-25, protoxide of iron 3*9, protoxide of man- 

 ganese 0*3, hydrofluoric acid 0-8 (Bonsdorf). 



Nephrite is a very tough compact variety, related to tre- 

 molite. Color light-green or blue. It breaks with a splin- 

 tery fracture and glistening lustre. H. = 6-6*5. G. = 3. It is 

 a magnesium-calcium amphibole. Nephrite is made into im- 

 ages, and was formerly worn as a charm. It was supposed to 

 be a cure for diseases of the kidney, whence the name, from 

 the Greek, nephros, kidney. In New Zealand, China and 

 Western America, it is carved by the inhabitants, or pol- 

 lished down into various fanciful shapes. It is called jade; 

 but the aluminum-sodium silicate, called jadeite, is the stone 

 most highly prized of all those that are called jade. Much 

 of the mineral from China called jade is prehnite. 



n. DARK-COLORED VARIETIES. 



Cummingtonite is a magnesium-iron amphibole. Color 

 gray or brown ; usually fibrous. Named from the locality 

 where found, Cummington, Mass. 



