EXTRA-LIMITAL SPECIES. 
453 
NITRE. 
Nitrate of Potash. Cleaveland, 
Colour white. In capillary crystals and crusts. Transparent to semi-transparent. Hard¬ 
ness 2.0. Sp.gr. 1.94. Dissolves in water. Composed of nitrate of potash, and several 
salts of lime, in variable proportions. 
With nitrate of lime and other salts, in the salt-petre caves of Kentucky, &c. 
PETALITE, 
Colour white or reddish white. In lamellar masses. Lustre glistening. Translucent. 
Hardness 6.0. Sp. gr. 2.44. Before the blowpipe, it melts only on the edges. Composed 
of silica 79.21, alumina 17.22, lithia 5.76. 
Bolton, Massachusetts. 
FINITE. 
Colour grey, greyish green or brown. Crystallized. Primary a hexagonal prism. Lustre 
sometimes resinous. Opaque. Hardness 2.0 to 2.50. Sp. gr. 2.75 to 2.78. Whitens 
before the blowpipe, and fuses on thin edges, but does not melt. Composed of silica 55.96, 
alumina 25.48, potash 7.89, soda 0.39, peroxide of iron 5.51, magnesia with manganese 
3.76, water 1.41. 
Lancaster in Massachusetts, and Haddam in Connecticut. It has been thought to be a 
variety of mica. 
POLYMIGNITE. 
Colour black. In prismatic crystals. Primary a rhomboidal octahedron, the dihedral 
angles of which are 136° 28', 116° 22' and 80° 16h Lustre imperfect metallic, but brilliant. 
Hardness 6.5. Sp. gr. 4.77 to 4.85. Infusible before the blowpipe. Composed of oxide 
of titanium, zirconia, yttria, oxide of iron, etc. 
Beverly, Massachusetts (Shepard). 
PURPLE COPPER. 
Variegated Pyritous Copper. Cleaveland. 
Colour between copper-red and tombac-brown. Streak pale greyish black and shining. 
Crystallized and massive. Primary a regular octahedron. Lustre metallic. Rather sectile. 
Hardness 3.0. Sp.gr. 5.00. Melts before the blowpipe. Composed of copper 61.07, 
sulphur 23.75, iron 14.00, silica 0.50. 
Chesterfield, Massachusetts ; Perkiomen, Pennsylvania. 
