Gemstone usually found in. For example, diamonds, which have a cubic crystal system, are often found as octahedrons. Gemstones are classified into different "groups", "species", and "varieties". For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow) and morganite (pink), which are all varieties of the mineral species beryl. Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture and luster. They may exhibit pleochroism or double refraction. They may have luminescence
Hooker Emerald Brooch Emerald at the centre of the brooch. Ten pairs of baguette-cut diamonds project between the spokes from behind the emerald towards the platinum band. The Hooker Emerald itself weighs . It measures to a side and is remarkably free of inclusions for its size. The gem's cut gives the appearance of a series of concentric squares within the gemstone (known as a beveled square emerald cut.) In total, the brooch contains approximately of diamonds. The Hooker Emerald was extracted from an unidentified mine in Colombia in the 16th or 17th century. The rough emerald was sent to Europe by Spanish