376 MINERALOGY 



other forms as the cube, tetragonal and trigonal trisoctahedrons-, 

 occur but are very rare ; also granular or massive. 



The only deposit of franklinite of any importance is at Franklin 

 and Stirling Hill, New Jersey, where it occurs in lens-shaped 

 masses, in a crystalline limestone, and associated with willemite and 

 zincite. This deposit has been worked for years. After the separa- 

 tion of the willemite and zincite mechanically, the zinc is volatilized 

 and collected either as oxide or spelter as the case may be; the resid- 

 ual, iron and manganese, is reduced to " spiegeleisen," an alloy 

 used in the Bessemer steel process. 



CHROMITE 



Chromite. Ferrous chromite, FeCr 2 O 4; ; FeO = 32.0, Cr 2 O 3 

 = 68.0 ; Isometric ; Type, Ditesseral Central ; Common forms, 

 o(lll), d(110); Cleavage, none; Brittle, fracture uneven; 

 H. = 5.5; G. = 4.32-4.57; Color, brownish black to gray or 

 yellowish ; Luster, metallic to submetallic, dull or greasy ; Streak, 

 brown to grayish brown ; Opaque. 



B.B. Infusible ; with borax in O. F. yields an emerald green 

 bead, which treated with KNO 3 in O. F. and dissolved in water 

 and several drops of acetic acid yields a yellow precipitate with 

 lead acetate (PbCr0 4 ). Insoluble in acids, but easily decomposed 

 when fused with sodium peroxide. 



General description. Crystals are octahedral in habit ; other 

 forms even in combination are rare. Chromite is more often mas- 

 sive, granular, or disseminated in rounded grains. 



In rock sections it appears usually in scattered rounded grains ; 

 in very thin sections it may be brown or reddish in color, but opaque 

 otherwise, and not to be distinguished from magnetite except by 

 means of chemical tests. 



Chromite is associated with the basic magnesian rocks, as perido- 

 tites and their alteration products, like serpentine, and while 

 widely distributed in small amounts there are no large deposits in the 

 United States. It is mined in small amounts in California, but 

 most of the chrome ore used is imported from New Caledonia, 

 Greece, Canada, Newfoundland, and Portuguese Africa. 



Crystals occur at Texas, Lancaster County, and massive in various 

 localities in Chester County, Pennsylvania; at Baltimore, Mary- 

 land; also at the Reed Mine, Hartford, Maryland; in North 

 Carolina and Wyoming. 



