THE NONMETALLIC MINERALS. 



247 



The analyses given below l will serve to show the varying character 

 of the mineral: 



Composition of chromite from various localities. 



Chromite, like magnetic iron, is black in color and of a metallic lus- 

 ter, but differs in being less readily if at all attracted by the magnet. 

 On a piece of ground glass or white unglazed porcelain it leaves a 

 brown mark, and fused with borax before the blowpipe it gives a green 

 bead. 



Occurrence. Chromite is a common constituent in the form of dis- 

 seminated granules of basic eruptive rocks belonging to the peridotite 

 and pyroxenite groups and in the serpentinous and talcose rocks which 

 result from their alteration (Specimens Nos. 63032, 36845, U.S.N.M., 

 from Maryland and North Carolina). It is never found in true veins 

 or beds, though sometimes in segregated, nodular masses somewhat 

 simulating veins on casual inspection. Masses of pure material, like 

 Specimen No. 17288, U.S. N.M., from Lancaster, Pennsylvania (weight 

 1,000 pounds), are quite usual. The more common form, as noted 

 above, is that of detached granules, which when freed from the inclosing 

 rock form the ore known as chrome sand (Specimens Nos. 5179, 63032, 

 56310, U.S.N.M.), and small masses like Specimens Nos. 11681, 40320, 

 63032, TJ.S.N.M. 



Deposits of chromite are now being worked near Black Lake Station, 



1 As compiled from various sources in Wadsworth's Lithological Studies. Memoirs 

 of the Museum of Comparative Zoology, XI, Part 1, 1884, Cambridge, Massachusetts. 



