Since May is the emerald birthstone month I though the maybe we should spend a few minutes going over some of the properties of that gem.
It's widely believed that the best emeralds come from Colombia; hoverer, gems of exceptional quality can also come from many other locations and be equal to the finest of Columbian stones. Russia's Ural Mountains has produced fine gems, and the stones from Zambia and Brazil are often found of the finest levels of quality..
Brazil is by far the world's largest producer of emerald. Other sources are Afghanistan, Australia, India, Pakistan, the United States, Zambia and Zimbabwe.
Emeralds come in a variety green intensities. The have subtle side-tone hues of other colors, typically blur or yellow. Generally, the richer the green, the more valuable the emerald. Emerald are a 7.5 to 8 on the hardness scale, a making them suitable for jewelry, but best used in occasional wear pieces or jewelry which is not subjected to abuse, i.e., don't build a stone wall while wearing your emerald ring.
Emeralds usually have some inclusions. These inclusions are called jardin in the jewelry trade. Completely clean emeralds are exceptionally rare and very expensive. In fact completely clean emeralds should be tested as being synthetic, as clean and emerald don't ofter occur in the same gem.
Like most gemstones in the market today, emeralds are usually treated in some way to remove surface flaws and enhance color. The most common (and acceptable) technique is to oil the stone with a green-tinted oil to fill in surface cracks. The oil hardens and strengthens the stone, and improves its green color as well. Newer types of treatment are also used which can be superior to oiling. These treatments include epoxy-type treatments to fill and strengthen the gem.