Emerald--the green stone

EMERALD 

The emerald is a type of beryl. It's green – varying from blue-green to yellow-green! Emeralds are naturally fairly hard, (they are rated seven-and-a-half to eight on Mohs' scale) but aren't very strong. Emeralds are highly included (included means “material that is trapped inside a mineral during its formation”), so their resistance to breakage is poor.

Unlike diamonds, when specialists magnify the stone 10x to determine the quality, emeralds are graded by eye. If there are no visible inclusions, the stone is considered “flawless”. Stones that don't have fissures (or cracks) breaking the surface are very rare, and most of the time the emeralds are treated with oil to give it a better overall appearance. “Clean” stones with a vivid green colour and no more than 15% of other colours (e.g. blue or yellow), who have a medium to dark tone cost the most.

Emeralds were mined by the ancient Egyptians in Egypt (ever wonder where the Israelites got their emeralds from for Aaron's breastplate? They may have dug them up themselves!), and were also mined in India and Austria. Emeralds are also found in other countries; Australia, Bulgaria, Cambodia, Canada, China, Ethiopia, France, Germany, Italy, Kazakhstan, Madagascar, Mozambique, Namibia, Nigeria, Norway, Pakistan, Russia, Somalia, South Africa, Spain, Switzerland, Tanzania, United States, Zambia and Zimbabwe.

Emeralds are used for jewelry.

http://en.wikipedia.org/wiki/Inclusion_(mineral)
http://en.wikipedia.org/wiki/Emerald