510 



MINERALOGY 



olite, pyroxene, and vesuvianite. At Burgess, Ontario, hexagonal 

 prisms a foot in length occur in the limestone. These large crystals 

 always have a peculiar vitrified appearance, their edges are rounded 

 as if they had been partly fused. Apatite occurs commonly along 

 the Atlantic slope from Ontario to Georgia. It is associated with 

 the tin veins of Bohemia and Cornwall, where its origin is due, as is 

 also the cassiterite, to the chemical interaction of volatile fluorides 

 and chlorides. 



It is very peculiar that apatite, being quite soluble in acids and a 

 salt of a weak acid, decomposes in nature with difficulty. Under the 

 action of percolating waters containing carbon dioxide the calcium 

 phosphate passes into solution, to be again separated as various 



FIG. 515. Section of a Mica-diorite, showing a, Apatite; b, Hornblende; 

 c, Biotite ; e, Quartz ; and /, Feldspar partially Altered. 



secondary iron phosphates, as vivianite, Fe 3 (P0 4 ) 2 . 8 H 2 0, a 

 common mineral of clays ; also as dufrenite, Fe 2 (OH) 3 P04 ; 

 phosphosiderite, 2 FePO 4 . 3 H 2 O ; strengite, FeP0 4 . 2 H 2 O ; as 

 secondary aluminium phosphates, wavellite, A1 3 (OH) 3 (P0 4 ) 2 . 

 5 H 2 O; variscite, A1PO 4 . 2 H 2 O; turquoise, A1 2 (OH) 3 PO 4 . H 2 0. 



Artificial apatite has . been formed by heating calcium and 

 ammonium chlorides with calcium phosphate in a sealed tube at a 

 temperature as low as 150 C. It has been reported as a con- 

 stituent of some slags, but this has never been confirmed by analy- 

 sis. Either chlor- or fluor-apatite may be produced in the dry fusion 

 of sodium phosphate with either calcium chloride or calcium 

 fluoride as the case requires. 



