COMPOUNDS OF CALCIUM. 207 



grayish oblique rhombic prisms. Insoluble. H. =5-5*5. G.=3'l. 



From Salzburg, Austria. Kjeralfine is near wagnerite. 

 Hiirnisite and Bcesslerite are hydrous calcium arsenates. 

 Luneburgite. A magnesium boro-phosphate, from Luneburg. 



Magnesite.— Magnesium Carbonate. 



Rhonibohedral. R : 72=107° 29'. Cleavage rhomboliedral, 

 perfect. Often massive, either granular, or compact and 

 porcelain-like, in tuberose forms ; also fibrous. 



Color white, yellowish or grayish-white, or brown. Lus- 

 tre vitreous ; fibrous varieties often silky. Transparent to 

 opaque. H.=3 — 4*5. G. = 3. 



Composition. Mg0 3 C = Carbon dioxide 52'4, magnesia 

 47'6 = 100. Infusible before the blowpipe. After ignition 

 has an alkaline reaction. Nearly insoluble in cold dilute 

 hydrochloric acid, but dissolves with effervescence in hot. 



Diff. Resembles some varieties of calcite and dolomite ; 

 but from a concentrated solution no calcium sulphate is 

 precipitated on adding sulphuric acid. The fibrous variety 

 is distinguished from other fibrous minerals by its efferves- 

 cence in hot acid, which shows it to be a carbonate. 



Ob*. Magnesite is usually associated with magnesian 

 rocks, especially serpentine. At Hoboken, N. J., it occurs 

 in this rock in fibrous seams ; similarly at Lynnfield, Mass.; 

 and in Canada, at Bolton, imperfectly fibrous, traversing 

 white limestone. 



When abundant it is a convenient material for the manu- 

 facture of magnesium sulphate or Epsom salt, to make 

 which, requires simply treatment with sulphuric acid. 



Hydromagnesite. A hydrous magnesium carbonate. Occurs with 

 serpentine, at Hoboken, but more abundantly in Lancaster Co. , Penn. 

 Dolomite. A magnesium and calcium carbonate. See page 219. 



CALCIUM. 



Calcium exists in nature in the state of fluorite, and this 

 is its only binary compound. It occurs in ternaries in the 

 state of sulphate, borate, columbate, phosphate, arsenate, 

 carbonate, titanate and silicate. The carbonate (calcite and 

 limestone) is one of the three most abundant of minerals. 

 The fluoride and sulphate, and some silicates, are also of 

 very common occurrence. 



