110 NEW YORK STATE MUSEUM 



The crystals of titanite are monoclinic and very varied in 

 form ; commonly of a wedge-shaped or tabular type (fig. 235) but 

 often prismatic in habit. Compact massive forms also occur 

 but lamellar varieties are rare. The luster is adamantine or 

 resinous and the color usually brown to black, 

 yellow or green, rarely rose-red. 



Titanite occurs as an accessory rock-forming 

 mineral in many igneous rocks, mostly of the 

 acidic feldspathic type and is more common in 

 Fig. 235 plutonic granular than in the volcanic forms. 



It is found in basic hornblende granites, sye- 

 nites and diorites and is very characteristic of the nephelin 

 schists, gneisses, etc.; also in granular limestone and in beds of 

 iron ore. It is commonly associated with pyroxene, amphibole, 

 wernerite, zircon, apatite, etc. and when found in cavities in 

 granite and gneiss often accompanies orthoclase and quartz. 



Handsome specimens are to be found in Ottawa and Renfrew 

 counties, Canada, and in Xew York in the Lake George region 

 of Essex county and in St Lawrence, Lewis, Orange and Putnam 

 counties. Transparent varieties are cut for gems. 



NIOBATES, TAXTALATES 



Cohimbite, tantalite 



The species columbite, an iron and manganese niobate, and 

 tantalite', an iron tantalate, grade into each other chemically to 

 such an extent that it is impossible to definitely separate the 

 two species. The normal formula for columbite is (Fe, Mn) 

 Nb 2 O e and that for normal tantalite is FeTa 2 G . The iron 

 and manganese vary widely and tin and wolfram are also often 

 present in small amounts. 



The crystals which are orthorhombic are of varied habit, some- 

 times occurring in short prismatic forms or in tabular prismatic 

 crystals flattened parallel to the macropinacoid. Heart-shaped 

 twins are quite common. It also occurs massive. The luster 

 is submetallic, often very brilliant, and the color black in opaque 

 varieties or brown in the more translucent occurrences. It is 

 frequently iridescent, particularly on the surfaces produced by 

 cleavage, which occurs in two directions at right angles. 



