BE ! \n 8, TITANATES, i i< 497 



tminnaline in schists ;it < 'h. >(([, Massachusetts; also at 



villc, Pennsylvania, and at the corundum lucalit ie> of North ( 'aru- 



lina and ( Jem-gin. 



Ottrelite, H 2 (Fe . Mn)Al 2 Si 2 O 9 , is a mica in which there is con- 

 sidrraMr manganese; H. = 6-7 ; G. = 3.3. It fuses with difficulty 

 and yields iron and manganese reactions and is usually dark gray to 



black. 



Clintonite is a bronze-colored mica occurring at Amity, New 



York. 



C.HLORITES 



The composition of the chlorites is complex and uncertain. 

 They are all hydrated decomposition products, probably formed of 

 mixtures of several isomorphous salts or types of salts, but just 

 what these types are is still unknown. When fused, their water is 

 driven off and they break down into a portion which is soluble, and 

 into an insoluble portion, of the nature of spinel. They may be 

 derived from the hydration and alteration of almost any ferro- 

 magnesian mineral containing aluminium, as they are all basic 

 orthosilicates of aluminium and ferrous iron. Some ferric iron 

 may replace the aluminium, and isomorphous elements replace the 

 ferrous iron, as manganese. When crystallized, they are mono- 

 clinic in symmetry, tabular and six-sided in habit, with a perfect 

 basal cleavage. The laminae are flexible and tough, but inelastic. 

 Their color is usually shades of green, as the name implies, except 

 where manganese is present, when they may be pink ; H. = 1-3.5 ; 

 G. = 2.65-2.96; Double refraction .001 to .009; Optically (); 

 Bx a A c = 0-8. 



B.B. They whiten and fuse on the edges to a black slag when 

 much iron is present, or a yellowish slag when it is absent. Yield 

 much water in the closed tube, about 12 per cent. ; decomposed 

 by sulphuric acid. 



Clinochlore, H 8 (Mg . Fe^A^SisOig, and orochlorite (ripidolite) 

 II \Ig . Fe) 23 Ali 4 Sii3O9o, are well-crystallized members of the 

 group, occurring in large hexagonal plates or curiously curved 

 prisms. Their crystals are often implanted on the edges in diver- 

 gent groups. They yield pressure and percussion figures as in the 

 true micas. Large rough crystals of clinochlore occur at West 

 Chester, Pennsylvania, and well-formed tabular crystals at Texas, 

 Pennsylvania. 

 2x 



