From classical to fantasy shapes, there are many different styles when it comes to cutting a stone. However, there are several factors to consider before doing so, such as the yield of the final stone compared to the rough, the inclusions, the colour, the shape of the rough stone, etc. 

Yield and inclusions In most cases, the goal is to keep as much material as possible while getting rid of as many visible inclusions as possible.

With high-end stones such as rubies, sapphire, emerald, spinel, etc., the choice of shape is based on the best yield compared to the rough as well as the need to remove as many inclusions as possible.

Stones such as quartz (amethyst, citrine, smoky quartz, etc.), some garnets and topazes, can be cut in all possible shapes or sizes without any problem. As these stones are more common, it is easy to find a rough that will fit the desired shape. And since they are relatively inexpensive, the yield relative to the rough is not as important.

Colour

Many stones such as sapphire and ruby, tourmalines, tanzanite and beryl will cause an optical phenomenon called pleochroism; that is, light is not absorbed in the same way from all angles. An angle can reveal a distinct shade of the colour (tourmalines) or a completely different colour (tanzanite and andalousite). This is an important factor to consider in order to get the best possible colour when cutting a stone.

Another factor to consider with colour is the presence of colour zoning. The best colour zoning example is found in watermelon tourmaline, which has very contrasting colours. In some cases, such as quartz (amethyst and citrine) or sapphires, colour zoning can be more subtle. The stone can be cut either to reveal the different colours or to highlight a single colour.

The shape of the rough

Gemstones are the result of a crystallization process and there are different crystalline systems, which results in different shapes of crystals. 

Beryl (emeralds, aquamarine and morganite), imperial topaz and tourmaline are found in elongated crystals. Most of the time, they will be cut into various elongated shapes like pears, ovals or cushions. Stones that crystallize according to other systems, such as sapphires, rubies, spinel, garnet and diamonds, will be cut rather in round or square cushion shapes.

Here are some examples of shapes and cuts: