138 



MINERALS AND GEOLOGY 



the immediate vicinity of the Apatite and Gale-Spar groups. The 

 fluorides generally, when treated, in powder, with hot sulphuric acid,, 

 evolve fumes of hydrofluoric acid which exert a strongly corrosive 

 action on glass. The powdered substance may be warmed with some 

 sulphuric acid in a platinum or lead crucible covered with a glass 

 plate, when the under surface of the latter will be quickly corroded. 

 In making the experiment, great care must be taken not to inhale the 

 evolved fumes, as these are highly injurious. See also under "Blow- 

 pipe Reactions/' in Part I.) 



106. Fluor Spar: Occasionally colourless, but more commonly 

 violet or amethyst-blue, dark blueish-green, pale-green, pale blueish- 

 grey, yellow, brownish, or rose- red, the edges and angles of many 

 crystals being more deeply tinted than the other parts, or sometimes 

 presenting a distinctly different tint or shade of colour. Streak, 

 white. Crystallization, regular; the crystals mostly cubes, or cubes 

 with bevelled edges (Figs. 80 and 81.) The corners of these cubes 

 break off very readily, in consequence of the strongly-pronounced 

 octahedral cleavage possessed by the mineral. H = 4.0 ; sp. gr. 3.1 

 3.2. Emits a blueish or other coloured phosphorescent light, when 

 moderately heated in the form of powder. BB, generally decrepi- 

 tates violently (see Part I), and fuses into an opaque white bead, 

 which becomes caustic after strong ignition. Decomposed, with evo- 

 lution of corrosive fumes, by hot sulphuric acid. The evolved fumes 

 consist of hydrofluoric acid, which strongly corrodes the surface of 

 glass. Average composition : fluorine 48*72, calcium (the metallic 

 base of lime 51.28. 



Fluor Spar occurs very 

 generally in association with 

 metallic ores in veins. It 

 also forms per se, or in con- 

 nection with calcite, the 

 substance of many narrow FIG. so. FIG. si. FIG. 82. 



veins ; and it occurs likewise in cavities and small fissures in lime- 

 stone and other rocks, and is occasionally disseminated through beds 

 of crystalline limestone. The finest examples hitherto discovered in 

 Canada, have been obtained from a large vug or cavity in a vein of 

 amethyst-quartz on the north-east shore of Thunder Bay, Lake 

 Superior. The fluor spar from this spot forms large cubes of two or 





