erally
reniform and massive, whence it is often called kidney-ore. Though dark
steel-gray when polished, it has a reddish-brown or cherry-red streak,
from which its name hematite, or " blood-stone," is derived. The lustre
is highly metallic. Hardness, 5.5 to 6.5; specific gravity, 4.5 to 5.3.
It is found in Europe, South America, and the United States.
Hypersthene,
or Labrador hornblende, resembles home-blende, but differs in cleavage
and the angles of its crystals. It is found in crystalline masses in
Labrador and in various localities of northern and central Europe, the
Isle of Skye, and the United States. Composition varies: silica, 54;
magnesia, 24; protoxides of iron and manganese, 22. Specific gravity,
3.39. Lustre pearly to metallic; translucent to opaque. Brittle. Some
varieties fuse under the blow-pipe; others fuse with difficulty to a
grayish green semi-opaque glass. Color, grayish, greenish, and jet
black, green, and dark brown.
Iolite, dichroite, or cordierite, is named from the Greek iodes, violet.
Crystallization trimetric. In rhombic and hexagonal prisms, and as
pebbles. Hardness, 7 to 7.5; brittle; specific gravity, 2.6 to 2.7.
Cleavage indistinct; crystals often separable into layers parallel to
the base. Lustre vitreous to greasy; transparent to translucent. Very
flawy. Its pleochroism is remarkable and it sometimes shows, when
properly cut, a chatoyancy similar to the corundum star-stones.
Composition: silica, 48.3; alumina, 32.5 ; magnesia, 10; and ferrous
oxide in slightly varying proportions. It melts with difficulty on the
edges under the blow-pipe, and is partially decomposed by acids. It
undergoes a gradual alteration if exposed to air and moisture,
absorbing water and assuming a foliated micaceous structure. The blue
variety is known as water-sapphire. It is also found colorless; in
blue, and yellowish shades of white, gray, and brown; and in indigo and
violet. It is obtained in Ceylon, Greenland, various parts of Europe,
and the United States.
