the most famous amoung beryl group with formula Be3Al2(Si6O18) and hardness of 7.5-8.Despite his hardness can be brittle and must be handle with care in jewelry.
His color is due to chromium and sometimes vanadium content and the most valuable stones comes from Colombia,especially Muzo.Emerald is also mined in Zambia and Brazil as named the two most important location, small deposit are in Urals, and recently Etiophia.
The stones are oftend treated in the mines with cedar oil or similar oil ,but lots of stones in the market are opticon filled ( a type or resin filled into the fractures and sealed on surface )
This gem here comes from Colombia and it has minor oil treatment.
The color is much nicer in reality,for some reason is difficult to catch the real tone blue-green of emeralds.Very small inclusions.
Size: 8x6.1x4.8 mm.