GUIDE TO THE MINBRALOGIC COLLECTIONS 



117 



Columbite often occurs in granite and pegmatite veins, in 



mica, and, in the Greenland locality, in cryolite; it has been 

 found in gold washings in the Urals. In the United States it 

 is found in Maine, New Hampshire, Massachusetts, Connecticut, 

 New fork, Pennsylvania, Virginia, North Carolina, Colorado, 

 South Dakota and California. 



I'HOSPHATES, ARSENATES, VANADATES, ANTIMONATES 

 Monazite (Ce 5 La,Di)P0 4 

 Monazite is a phosphate of the cerium metals, with some 

 thorium and silicon possibly present as mechanical impurities. 



It occurs in small monoclinic crystals (fig. 

 236) often flattened parallel to the orthopina- 

 coid; also in disseminated grains or as sand 

 and sometimes in angular masses. The lus- 

 ter is resinous and the color hyacinth-red, 

 brown to yellow. 



Monazite in the form of sand is quite 

 abundant in certain parts of Brazil; it also 

 occurs as a constituent of the gneiss rock of 

 North Carolina and South Carolina. Monazite 



It is the chief source of the thorium which is now extensively 

 used in the manufacture of mantles for incandescent gas fix- 

 tures. 



Apatite group 

 Apatite (phosphate rock) Ca 5 (Cl,F) (P0J 3 

 Under this head are included the subdivisions fluor-apatite and 

 chlor-apatite. The former is a calcium phosphate with calcium 

 fluorid and the latter a calcium phosphate with cal- 

 cium chlorid. Intermediate compounds contain both 

 fluorin and chlorin in varying amounts. 



Apatite crystallizes in the pyramidal group of the 

 hexagonal system. The crystals are prismatic in 

 oabil commonly terminated by the unit pyramid (fig. 

 ■I'M) and sometimes with ill.- additional modification 

 of Hi'- base; occasionally the prismatic crystals 

 are short or tabular and shovi the modification of 

 the third ord.r pyramid ias in specimens from Knap- 

 penwand in the Tyrol). Compacl massive varieties have a 

 globular or reniform structure and are often found in rocklike 



log. 237 

 Apatite 



