COLUMBATES, IMK >si'll \TI:S. \ \v\n\Ti.s 



GMfeiterite, and sulphides al Khren!ri''der-dorl'. Saxony. Crystals 



rich in lonns have ;ilso been described from Branehville, < 'on- 

 necticiit, ;nl Alexander < 'oimty, North Carolina. 



Chemically then- an- two coiupouiKls, a chlor-apatite and a fluor- 

 apatite, which are isomorphoiis and occur in the >ame crystals. It 

 i< rarely that one occurs wit hoiil the other : in addition the chlorine 

 or fluorine may be replaced by hydroxyl (OH) ; such specimen.-- will 

 yield a little water in the closed tube. Phosphatic rock found in 

 the South and West is of the nature of apatite, but of organic origin ; 

 a bone phosphate, phosphatic nodules, coprolites, all of which are 



FIG. 514. Apatite. Snarum, Norway. 



phosphates of calcium, but not crystalline, and therefore their com- 

 position varies greatly. 



Extensive beds of these phosphates are found in South Carolina 

 and the Gulf states ; after treatment with sulphuric acid they form 

 the superphosphates of the fertilizer industry. 



Apatite occurs in rocks of all descriptions and under variable 

 conditions. In igneous rocks it is always well crystallized, elon- 

 tialed parallel to the vertical axis ; one of the very first minerals to 

 separate from the magma; it appears as inclusions in all others, 

 even penetrating the magnetite. 



In rock sections it is colorless, with a hexagonal outline, or elon- 

 gated when cut nearly parallel to c; such sections usually show a 

 tran verse parting, but the basal cleavage is seldom observed in sec- 

 tions. The relief is well marked ; interference colors are grays of the 

 first order. Apatite is a common mineral in the metamorphic rocks 

 and crystalline limestones, where it is associated with titanite, scap- 



