has boon grouped with the sesquioxides, as TijOj is iso- 

 i phous with Fo^jOs, but there is no doubt but that ilmenite is a 

 inct:ititanate and is out of place here as placed by Dana's 

 cl:iific:itiun. Magnesium and manganese are both bomorphoufl 

 with ilinonite, and pyrophane is the manganous metatitanate, 

 MnTiOs. 



llmniito occurs associated with magnetite and under the same 

 conditions, as a primary constituent of igneous rocks ; as such it is 

 one of the first minerals to separate from the magma. It is more 

 abundant in the basic rocks, as the diorites, diabases, and basalts. 

 It also occurs in schists, gneisses, metamorphic rocks, argillites, 

 aiul slates. 



In rock sections it is opaque and appears brownish by reflected 

 light. When in crystalline outline it is elongated, but occurs more 

 often as rounded grains and irregular masses, not to be distinguished 

 from magnetite or chromite but by chemical tests. Ilmenite 

 is often altered, resulting in a clear or translucent boundary, or area 

 surrounding the opaque masses, composed of a highly doubly re- 

 fracting substance termed leucoxene, formed by the decomposition 

 of the ilmenite, and which has been identified as perovskite 

 (CaTiO 3 ), as titanite, and again as anatase. Ilmenite occurs in 

 large masses at Bay St. Paul, Quebec, also in Orange Co., New 

 York, associated with serpentine, spinel, rutile, and chondrodite ; 

 at Litchfield, Connecticut; at Chester and South Royalston, 

 Massachusetts. The largest crystals of ilmenite, some of which 

 weigh sixteen pounds or more, have been found in a diorite at 

 Kragero, Norway. As an accessory in igneous rocks ilmenite is 

 very widely distributed. 



Ilmenite finds but little use in commerce; it is used as linings in 

 puddling furnaces, but owing to the difficulty of handling it in the 

 blast furnaces it is not used as an iron ore, though at the present 

 time titanium steel is being tried for rails with encouraging results. 

 Artificially ilmenite has been formed by heating a mixture of me- 

 tallic iron, ferric oxide, and amorphous titanic oxide in a sealed 

 tube to 270-300 C. 



OXIDES OF THE RO* TYPE 



CASSITERITE 



Cassiterite. Stream tin ; Tin binoxide, SnO ; Sn = 78.6, 

 O = 21.4; Tetragonal; Type, Ditetragonal Equatorial ; c = .6723; 

 001 A 101 =33 54'; 110,111=46 27'; Common forms, 



