MANUAL OF NATURAL HISTORY. 603 



Salts of baryta tinge flame yellow, sulphuric 

 acid throws down a heavy white precipitate 

 with those which are soluble. Symb. Ba. 



3. FAMILY. Strontiides. Minerals containing com- 



pounds of Strontium. Occur, 1, as Sulphate 

 of Strontia or " Celestine/' in right rhombic 

 prisms, H. 3-3*5, sp. gr. 3'9, bluish-white, 

 very brittle ; 2, as Carbonate or " Strontia- 

 nite," trimetric, often fibrous or granular, 

 H. 3*5-4, sp. gr. 3*6, greenish, brittle ; 3, 

 combined with Baryta, as "Barystrontianite," 

 in Orkney. Salts of strontia colour flame 

 deep red, those which are soluble act with 

 sulphuric acid like those of Baryta. Symb. Sr. 



4. FAMILY. Calciides. Minerals containing com- 



pounds of Calcium. Occur 1, as Sulphate of 

 Calcia (lime) or "Gypsum/' in right rhombic 

 prisms, sp. gr. 2*3, H. = T5 2 ; when tran- 

 sparent it is Selenite, when massive Alabaster, 

 when fibrous Satin-spar, and when an- 

 hydrous, H. = 3 3*5, it is Anhydrite ; 2, as 

 Carbonate, rhombohedral, sp. gr. 2*6, H. = 

 2*5 3*5, when in transparent crystals it 

 is Calcareous-spar or Iceland-spar; when 

 massive, Limestone; when compact and finely 

 crystallized, Marble; when bituminous, Stink- 

 stone; when earthy, Chalk; when projecting 

 from the roof, or on the floor of caverns, &c., 

 Stalactites or Stalagmites; when encrusting 

 Calcareous-tufa, and when in rhombic-prisms, 

 H. = 3 5 4, it is Arragonite; 3, as Phosphate 



DD 2 



