GUIDE TO THE MINEKALOGIC COLLECTIONS 73 



spinel ruby or balas ruby, which often rivals the oriental ruby 

 in color and fire. 



Spinel occurs in limestone, gneiss, serpentine and other 

 metamorphic rocks. Spinel ruby is abundant in Ceylon and 

 Burma and has been obtained from Hamburg N. J. and Orange 

 county, N. Y. Crystals of spinel are found in many parts of 

 North Carolina and Massachusetts and near the boundary line 

 between New York and New Jersey. 



Magnetite (magnetic iron ore) FeO.Fe.O3 



Magnetite is composed of iron sesquioxid and iron protoxid 

 and contains 72.4$ iron and 27.6$ oxygen. 



Magnetite crystallizes in isometric forms closely resembling 

 those of spinel. Parting parallel to the octahedron is often 

 developed (see specimen from Mineville N. Y. 

 in N. Y. state mus. collection). Massive 

 varieties have laminated, coarse or fine 

 granular and compact structure (pi. 4 2 ). 

 Magnetite has a metallic or submetallic 

 luster, is black in color and is strongly 

 magnetic. A variety known as lodestone is 

 a natural magnet (pi. 21 2 ). Magnetite 



Magnetite occurs mostly in crystalline rocks and is of uni- 

 versal distribution. Extensive beds are found in the Archaean 

 formation of northern New York and in the Adirondack region, 

 as well as in Saratoga, Herkimer, Orange and Putnam counties 

 of the same state, 1 the former deposits being to a considerable 

 extent titaniferous. 



Magnetite is extensively mined for iron. 



Franklinite (FeMnZn)0.(FeMn) 2 3 



Franklinite is an iron, zinc and manganese ferrate and man- 

 ganate of iather complicated formula and varying relative 

 quantities. 



The isometric crystals of franklinite are octahedral in habit 

 and are generally characterized by rounded edges, otherwise 

 they resemble those of magnetite. Franklinite also occurs in 

 rounded grains and in compact masses, hi color and luster it 



»N. Y. state inns. P.ul. 7. 1889. 



