Carat :
The carat (ct) is a unit of mass equal to 2 g. Carat is used for measuring the weight of gemstones.
Emerald :
Emerald is a gemstone, a variety of beryl colored in green by trace amounts of chromium, vanadium and sometimes iron. Emerald frequently contain many inclusions, with a result of poor resistance to breakage making their cutting very difficult.
Brilliant cut :
The modern brilliant cut was developed by Marcel Tolkowsky in 1919. It consists of 58 facets (or 57 if the culet is excluded). It is the most popular modern cut because it provides maximized light return through the top of the diamond.