204 



DESCRIPTIVE MINERALOGY. 



CLASS V. 



ALKALINE-EARTHY MINERALS. 



Composed of one or jno7-e alkaline earths, Baryta, Strontia, Lime or Magnesia, combined 

 with water or an acid, and frequently containing some metallic oxide. 



ORDER I. BARYTA. 



1. Heavy Spar. 



HEAVY SPAR. 



[From its great specific gravity, as compared with other non-metalHc minerals.] 



Baryte Sulfatee. Hauij, — Sulphate of Barytes. CleaveUmd and Thomson. — Prismatic Heavy Spar. JmiKsm. 

 — Prismatischer Hal-Baryte. Moks. — Barytes. PhiUips. — Barytine. Bcudant. — Heavy Spar. Shcpard and 

 Dana. 



Fig. 29. Description. Colour, when pure, snow wliile ; but it is some- 



times gi'ey, black, blue, green, yellow, red and brown. It occurs 

 regularly crystallized, also massive and disseminated. Primary 

 form a right rhombic prism. Fig. 29. M on M' 101° 42'. Clea- 

 vage parallel to M and M', perfect. Fracture uneven, splintery and 

 earthy. Lustre resinous or pearly, inchning to vitreous. From 

 transparent to opaque. Brittle and very easily frangible. Hardness 

 from 3.0 to 3.5. Specific gravity from 4 . 30 to 4 . 70. Before the 

 blowpipe, it decrepitates, and is with difficulty fused into a white 

 enamel. With soda, it is converted into sulphuret of barium, which, when dissolved in a dilute 

 acid, gives out sulphuretted hydrogen. 



When pure, the great speciiic gravity will usually distinguish this mineral from others which 

 it resembles. Celestine, when lield for some time in the reducing flame, and then moistened 

 with a drop of muriatic acid and held to the blue part of a candle flame, colours it beautifully 

 purple ; which is not the case with heavy spar. Witherite and strontianite dissolve with effer- 

 vescence in muriatic acid, while heavy spar is not acted on by it. It is, however, in some cases 

 quite difficult, without a detailed analysis, to distinguish between the salts of baryta and the 

 corresponding ones of strontia. 



