54 MINERALOGY. 



105. Fluor Spar. This is a fluorid of calcium, com- 

 posed of fluorine (one of the chlorine family) and calci- 

 um, which is the metallic base of lime. Neither of these 

 elements is ever found in nature. The, crystals of fluor 

 spar are the cube and the octahedron, and their seconda- 

 ries. Their colors, which are bright, are white, light 

 green, purple, and yellow ; sometimes rose-red and sky- 

 blue. Fluor spar phosphoresces brightly when put upon 

 hot iron, giving out various colors. It is an abundant 

 mineral in Derbyshire, England, and it is therefore often 

 called Derbyshire spar. In the massive* or granulated 

 form it is susceptible of a high polish, and vases, candle- 

 sticks, and various articles of ornament are made from 

 it. This mineral is present in very small quantities in 

 the teeth and bones of animals ; and as there must be a 

 supply of it for these structures from some source, it is 

 found in some plants, which, of course, have imbibed it, 

 as is the case with silex, from the earth. 



106. Apatite. Most of this mineral, whose beautiful 

 crystals present much variety of form, is a compound of 

 phosphoric acid and lime that is, a phosphate of lime. 

 But there is intimately incorporated with this fluor spar, 

 and a very small quantity of the chlorid of calcium. 



107. Salts of Magnesia. The sulphate of magnesia 

 was noticed in 61. The carbonate appears like some 

 of the varieties of carbonate of lime and dolomite. Sul- 

 phate of magnesia (Epsom salt) is often made from it. 

 This is done by means of sulphuric acid, the acid seizing 

 the magnesia and uniting with it, the carbonic acid gas, 

 of course, flying off as it is released. The hydrate of 

 magnesia is a compound of magnesia and water, the lat- 

 ter being nearly one third of the whole. JBorate of mag- 



* The term massive is applied to minerals that are imperfectly 

 crystallized that is, having parts of crystals huddled together in a 

 confused mass. The crystals thus massed together may be granular, 

 or fibrous, or laminated. We have a familiar example of the gran- 

 ular in marble, and of the laminated in slate rocks. 



