MICROCRYSTALLINE ROCKS and minerals have been used in decoration for thousands of years. The best known are the jades, lapis lazuli, and turquoise and there are many more which are suitable for carving work. Ancient civilizations such as the Egyptians, Chinese, and Sumerians used jade, lapis, and turquoise to make jewellery. South American Indians and the Maoris of New Zealand have been carving turquoise and jade for centuries.
Lapis lazuli is not a single mineral but a rock consisting of blue azurite with variable amounts of calcite and pyrite. The best, from Afghanistan, consists mostly of lazurite and is deep blue. It is 5.5 on Mohs' hardness scale and has a specific gravity of 2.7-2.9. There are other sources in the Soviet Union and Chile.
The name turquoise comes from the French Pierre turquoise meaning stone of Turkey, most of it in the past being sold in Turkey. It occurs in nodules and veins of green or blue. Copper makes it blue; iron makes it green. It has a specific gravity of 2.6-2.9 and a hardness of 5-6.
The Spanish conquerors of Mexico believed that the Indians' green stones would cure kidney ailments. They called them kidney stones or piedra de hyada and from this the word jade was derived. In Europe, the name was then given to material of the same colour and hardness which was imported from China. It was only in 1863 that they were proved to be two different minerals now called jadeite and nephrite.
Many other stones are popular for carving, mainly because of their colour. These include malachite, serpentine, blue john and rhodonite, as well as marbles and alabaster.