MICA. 193 



alumina 203, lime 6 1, protoxyd of manganese 4*7, potash 11*0, lithia 

 2-8, soda 22, fluorine 102, chlorine 1*2. 



Lepidolite occurs at the albite vein in Chesterfield, Mass., and at 

 Goshen in the same state ; also at Paris, Me., with red tourmalines, and 

 near Micldletown, Ct. 



Fuchsite. A green mica from the Zillerthal, containing nearly 4 

 per cent, of oxyd of chromium. 



Biotite. Resembles common mica or muscovite, but crystals usually 

 right prisms, and angle between the optical axes 

 only 1 or 2 degrees or less ; while in muscovite 

 the angle is 56 to 75 degrees. The form is usually 

 regarded as h p xngonal and not trimetric. Colors 

 mostly dark green to black, sometimes white. H 

 =2-5—3. Gr=2*7— 3*1. 



Composition: essentially like garnet. A variety from Monroe, N. 

 Y., afforded Smith and Brush, silica 39*9, alumina 15*0, peroxyd of 

 iron 7*7, magnesia 237, soda 1*1, potash 9'1, water 1*3, fluorine 0*9, 

 chlorine 0-4. Biotite is a magnesia mica. 



Obs. Occurs at Vesuvius, at Greenwood Furnace in Monroe, N. Y., 

 and elsewhere. Most of the black and greenish-black micas are biotite. 



Phlogopite. A mica, near biotite in the form of 

 the crystals, but angle between the optical axes 5 to ^^ p 

 20 degrees. Form trimetric. Color usually brown, 

 yellowish brown, sometimes white. 



Composition : a variety from Edwards, N. Y., af- 

 forded Craw, silica 40*15, alumina 17*36, magnesia 28*10, potash 10*56, 

 soda 0*63, fluorine 420. 



06*. Occurs in granular limestone, being characteristic of that rock. 

 Found at Gouverneur and other places in northern New York, War- 

 wick, Orange Co., <fec. 



Margarite, or Pearl Mica. In hexagonal prisms, having the struc- 

 ture of mica ; and also in intersecting laminae. Luster pearly, approach- 

 ing talc, hut differing from that mineral in being a silicate of alumina 

 instead of magnesia. Color nearly white, or gray. It intumesces and 

 fuses before the blowpipe. From Sterzing in the Tyrol, associated with 

 chlorite. Emerylite and diphanite belong here. 



Euphyllite is a new species, related somewhat to margarite, and 

 found associated with emerylite and corundum in Pennsylvania and 

 elsewhere. Rather brittle. 



Margarodite, or Schistose talc of Zillerthal, is near common mica, 

 but contains 4 or 5 per cent, of water. 



Lepidomelane. A black iron-mica, occurring in six-sided scales or 

 tables aggregated together. It contains silica 37*4, alumina 11*6, per- 

 oxyd of iron 27*7, protoxyd of iron 12*4, magnesia and lime 0*3, potash 

 92, water 0*6. From Warmland. Ottrelite (which includes the phyl- 

 lite from Sterling, Mass.,) is an allied mineral occurring in black scales, 

 disseminated through the rock. 



What are other kinds of mica ? 



