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.
The finest specimens are found in the Urals—a block three and a half feet square, being valued at 525,000 roubles.
Jet.
The making of jet or mourning jewelry was once a very large industry in France and England, and even now Whitby jet is well known in commerce.