Hematite.
Hematite was once largely used to engrave upon, many of the ancient intaglios being on this mineral. It is now cut to simulate black pearls, and is also used in the cheaper jewelry, both engraved and cut cabochon.
Hematite has the hardness of 5.5 to 6.5, and specific gravity, 4.2 to 5.3; it is opaque, and shows a red streak when scratched. It is composed of:
| Iron | 70 |
| Oxygen | 30 |
The colors of hematite are dark-steel gray to iron-black, and sometimes brownish- to blood-red. The lustre is highly metallic, with slight iridescence.
The island of Elba, France, Switzerland, Italy, Norway, Sweden, Bohemia, England, Brazil, Chili, Canada, Spain, and the United States are places where hematite is found. The Germans call this mineral “blood-stone,” and it is also known as specular iron ore and iron glance.
Obsidian.
Obsidian, or volcanic glass, does not occupy a high position as a gem or as an ornamental stone, but its antiquity and occasional use among the agates and semi-precious stones will justify its mention.
This mineral is a melted lava, and consists of silex, alumina, and a little potassa, soda, and oxide of iron. Obsidian is 6 to 7 in hardness, has a specific gravity of 2.25 to 2.8, is sometimes transparent but mostly translucent to opaque, and is vitreous to metallic in lustre. It is brittle and not easily attacked by acids. It melts before the blow-pipe and takes a high polish.
Obsidian comes from volcanoes, and is found in Iceland, Teneriffe, Lepare islands, Peru, Mexico, Sicily, and on all volcanoes. The color is velvety-black to gray, brown, greenish-black, yellow, blue, bottle-green, and white, seldom red, and often with black or yellow spots or veinings.