62 MINERALOGY. 



124. Pyroxene. This is a very common mineral, and 

 has many varieties. The colors also are various, being 

 shades of green from the lightest to the darkest. One 

 variety is even white. One of the additional oxyds is 

 lime, which differs in quantity very much in the different 

 varieties. Pyroxene occurs in various rocks granite, 

 limestone, the lavas, etc. 



125. Hornblende. This constitutes a large part of 

 some rocks, as trap and some kinds of slates, giving to 

 them great toughness. Like pyroxene, it contains lime, 

 and some of its varieties it is difficult to distinguish from 

 that mineral. Some of its varieties are beautiful. The 

 famous asbestos is a very remarkable one, being arranged 

 in such slender silky fibres that it may be woven like 

 cotton or linen into cloth. This cloth is incombustible, 

 and, when soiled, can be effectually cleaned at once by 

 putting it into the fire. The Greenlanders use asbestos 

 for lamp-wicks, and in ancient times it was used for this 

 purpose in the temples, its incombustibility being thought 

 to give it a sacred character. Amianthus is a variety of 

 asbestos which has a satin lustre. In Siberia and Spain, 

 gloves, ribbons, and purses are made of it. The differ- 

 ence between the tough hornblende that we find in rocks 

 and this very delicate variety of it is no greater than 

 that between common wood and the delicate varieties 

 of wood which we see in the forms of cotton and linen, 

 and in the textures of leaves, flowers, etc., as noticed in 

 511, Part II. 



126. Alumina. This is an oxyd of aluminum, a metal 

 which is never found in nature, but is obtained artificial- 

 ly from its compounds. Though this metal has been lit- 

 tle known till lately, it is coming into considerable use, 

 especially among the French, on account of qualities 

 which are noticed in 238, Part II. The oxyd alumina 

 is familiar to us in the form of emery. This is granular. 

 But it also appears in various crystalline forms, and, 

 when clear, is exceeded in costliness only by the dia- 



