About the Properties of Obsidians and Malachites

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 semiprecious 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.

Iceland agate lava, volcanic lava, and royal agate are all obsidian.

MALACHITE.

Malachite although sometimes used for jewelry, is now more largely employed for mosaic work and ornamental vases, and is sufficiently costly and rare to be classed amongst the precious stones.

Malachite is 3.5 to 4 in hardness; has a specific gravity of 3.6 to 4; is translucent to opaque; the lustre is vitreous to adamantine. It is attacked by acids, and melts before the blow-pipe. It is composed of:

Carbonic acid 20.

Protoxide of copper 71.8

Water 8.

Malachite occurs in emerald or verdigris green color, sometimes in alternating stripes of different shades of green, and occasionally in leek-to blackish-green.

Malachite is found in Russia, France, the Tyrol, England, Scotland, Ireland, Germany, Africa, Chili, Australia, and the United States.