1880.J NATURAL SCIENCES OF PHILADELPHIA. 311 



December 22, 1879. 



THE SO-CALLED EMERY-ORE FEOM CHELSEA, BETHEL TOWNSHIP, 

 DELAWARE COUNTY, PENNSYLVANIA. 



BY F. A. GENTH, JR. 



At the November meeting of this Section, Dr. Cardeza called 

 the attention of the members to a garnet rock, mined as emery- 

 ore, at Chelsea, Bethel Township, Delaware Co., Pa., and subse- 

 »iuently left it with me for analysis. 



The rock is composed almost exclusively of rounded rhombic- 

 ilodecahedral grains of red garnet, varjdng in size from a fraction 

 of a millimetre to over one centimetre ; also a little quartz, biotite, 

 muscovite, and magnetite. It is very friable, being easily crushed. 



Its fracture is uneven, excepting in some of the larger grains, 

 which are so much intersected by mica, that, when struck by a 

 hammer, they break into angular fragments, apparently showing a 

 crystalline cleavage. Specific gravity = 4.028. 



An analysis of the smaller and purer grains, obtained by wash- 

 ing and picking out, gave : 



SiO, = 41.11 



Fe.p3 = 2.11 



Al.Os = 21.60 



FeO ^ 25.86 



MnO = 2.22 



CaO = 1.89 



MgO = 5.41 



100.20 

 which proves it to be an ordinary iron-alumina garnet. 



