COMPOUNDS OF CALCIUM. 207 
grayish oblique rhombic prisms. Insoluble. H.=—5-5:5. G.=3:1. 
From Salzburg, Austria. Ajerulfine is near wagnerite, 
Hernisite and Iessierite are hydrous calcium arsenates. 
Liineburgite. A magnesium boro-phosphate, from Liimneburg. 

Magnesite.— Magnesium Carbonate. 
Rhombohedral. R : R=107° 29’. Cleavage rhombohedral, 
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. 
Jumposition. MgO,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. ‘he fibrous variety 
is distinguished from other fibrous minerals by its efferves- 
cence in hot acid, which shows it to be a carbonate. 
Obs. 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. Ocenrs 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. 
