KINDS OF ROCKS. 455 



7. Pyrophyllyte and Pyrophyllite Slate.— Like the preced- 

 ing in appearance and soapy feel, but having the composi- 

 tion of pyrophyllite (p. 306). The color is white and gray 

 or greenish white. Occurs in North Carolina. One of the 

 varieties from the Deep River region is used for slate pen- 

 cils. Metamorphic. 



9. IRON-ORE ROCKS. 



1. Hematyte. (Specular Iron Ore). — Hematite (p. 176), in 

 metamorphic beds. Color iron gray, and lustre bright me- 

 tallic, but varying to red and jaspery. Has the hardness of 

 crystallized hematite and its red streak. Constitutes beds 

 of" great thickness in Archaean regions and thinner beds in 

 formations of later geological age ; alternates with horn- 

 blendic, chloritic, micaceous, and gneissoid, and sometimes 

 calcareous rocks, and often contains siliceous or jaspery 

 layers. 



Varieties — a. Iron-gray ; the ordinary massive kind. b. Red ; 

 resembling a hard red jasper, into which it sometimes passes, c. Con- 

 taining martite; the octahedral crystals of martite having originally 

 been magnetite, and showing that they are changed to hematite by 

 their red streak, d. Foliated ; sometimes called micaceous iron ore, 

 in allusion to the foliation, e. Epidotic. 



In large beds in the Archaean of Canada, St Lawrence Co., N. Y., 

 at Marquette, Northern Michigan, Missouri. At Nictaux, in Nova 

 Scotia, in semi-metamorphic fossilif erous Devonian there is a bed six 

 feet thick. 



2. Itabyryte. — A mica schist consisting largely of hema- 

 tite in laminae of bright metallic lustre. 



3. Magnetyte. (Magnetic Iron Ore).— Magnetite (p. 178), 

 in metamorphic beds. Color iron gray to grayish black, 

 and lustre metallic ; never bright red. Strongly attracted 

 by the magnet, and hence often separated from the gangue, 

 after crushing it, by means of large electro-magnets. Con- 

 stitutes, like hematite, thick beds in Archaean regions, and 

 thinner in rocks of other periods. 



Varieties. — a. Massive, b. Granular, c. Epidotic. d. Hornblendic. 

 e. Chloritic. f. Titanic, g. Chondroditic ; as near Brewster, N. Y., 

 where chondrodite is the " gangue" of the ore. 



Metamorphic magnetite constitutes thick beds in the Archaean of 

 Canada, Northern New York, Orange Co., N. Y., Sussex C!q., N. J., 

 and occurs also in Virginia, east of the Blue Ridge, in Albermax-le, 



