ELIZABETHTOWN AND PORT HENRY QUADRANGLES 1 59 



In the clump of the Split Rock titaniferous ore body the writer 

 happened upon a few pieces, which had once formed the sides of 

 a narrow crevice. They were coated with smaU but briUiant crys- 

 tals which Mr H. P. Whitlock of the State Museum identified as 

 magnetite of the form shown by the accompanying figure which 

 lie kindly drew. The crystals are remarkable for the development 

 of the cube, a rare face in magnetite, and for the trigonal trisocta- 

 hedron. 



The following papers have dealt with the magnetite crystals 

 from Mineville : 



Birkinbine, John. Crystalline Magnetite in the Port Henr)^ N. Y. Mines. 

 Am. Inst. Min. Eng. Trans. 1890. 18:747. 



Kemp, J. F. j3estreifte Magnetitkrystalle aus Mineville, Lake Champlain 

 Gcbiet, Staat New York, Zeitschrift fiir Krystallographie,- 19:183. Notes 

 on the Minerals occurring near Port Henry, N. Y. Am, Jour. Sci. July, 

 1890, p. 62. 



Microcline, sec under Feldspar. 



Molybdenite, as is usual in the magnetic mines of the ancient 

 gneisses, occasionally appears in the pegmatitic streaks. In the 

 New Bed pits it has been observed as scales associated witli 

 pyrrhotite. 



Olivine is a common constituent of the gabbros but seldom if 

 ever in amounts sufficient to see without the microscope. 



PhlO'gopite appears in the quarries in the Grenville limestones 

 and ophicalcites, its characteristic association. 



Plagioclase, see under Feldspar. 



Pyrite is a rarity in the large mines and is only met in some 

 secondary veinlets. It does appear in some of the smaller and 

 ■leaner ore bodies but not, so far as known, in good crystals. 



Pyroxene being the name of a group, the several species under 

 it must be taken up separately. Hypersthene, the orthorhombic 

 member, is common in the anorthosites and gabbros, usually in the 

 microscopic way; but when the former are coarsely crystalline and 

 above all pegmatitic, the hypersthene assumes moderately coarse, 

 platy growths which give cleavage pieces. 



Diopside appears in the quarries in the Grenville limestones. 

 Once at the ophicalcite quarry a half mile north of Port Henry, 

 the writer happened on pockets of calcite, into which diopside, 

 brown hornblende and titanitc projected in such a way as to be 

 easily freed by weak acid. The diopsides vary from one tenth 

 to half an inch in length and possess shining faces adapted to 

 goniometrical measurement. They are usually white but shade to 

 pink and are translucent. They have, been measured and figured 



