A diamond is evaluated through four different characteristics which can be combined in several ways changing the value of the gemstone. Here you are the “four C’s rule”: Carat, Clarity, Colour and Cut. Among the “four C” the cut is the one that can be mainly influenced by the human being. The others are solely influenced by nature.
A ruby is a variety of corundum, a very allochromatic mineral. It is the only substance which has a hardness of 9 on the Mohs scale of mineral hardness. Corundum is called ruby when it has inclusions of chromium. In fact, the presence of this element makes the allochromatic corundum red. A ruby can have different shades of red from a very vivid one (this is the typical colour of the famous variety of ruby called “blood red” or “pigeon blood”) to a pinkish red.
A sapphire is a variety of corundum, a very allochromatic mineral. It is the only substance which has a hardness of 9 on the Mohs scale of mineral hardness. Corundum is called sapphire when it is an aluminium oxide. If the term “sapphire” is not preceded by an adjective that specifies the colour, it refers to the blue gem. However, there are natural sapphires of many different colours; such as yellow sapphire, pink sapphire or green sapphire. All of them are very valuable and used in the jewellery sector.
Emerald is a quality of beryl coloured green by the presence of chromium. Its characteristics are the green colour (with shades from blue – green to yellow – green), the vitreous lustre and a hardness of 7 on the Mohs scale of mineral hardness. The evaluation of emeralds is based on integrity of the gem, cut, colour and transparency; in particular, these last two parameters are the most important. Unlike diamonds, the emerald integrity is evaluated to the naked eye.