Tourmaline occurs in a seemingly endless variety of colours and hues. Broadly speaking, a tourmaline's colour may be classified as green, blue, pink, or yellow, but within each of these groups, there may be enormous variation in saturation of colour and hue. For instance, a few ways to describe colour in green tourmalines can range from "light mint" to "olive" to "olive with a brown tint" to "deep green" to "deep green with a blue tint" etc.
Tourmaline crystals are generally shaped like long cylinders with flat sides. If a stone is cut with the table parallel to the flat sides of the crystal, it will have a different colour and hue compared to stones cut with the table parallel to the ends of the crystal.
Generally a lot of tourmaline - particularly green and blue - is cut with the table of the gem running parallel to the flat sides of the crystal to optimise colour because cutting the other way can result in a stone that is too dark. Consequently, cutting for best colour may lead the lapidarist to favour a rectangular cut, as this produces optimal weight retention.
Green and blue tourmaline varieties also have the tendency to occur in long slender crystals, and when this occurs the only real practical cut is either rectangular or baguette. This is not so much the case when it comes to pink-coloured tourmalines and the cutter will often cut with the table parallel to the top of the crystal so as to produce a stone with a deeper saturation of colour.
Deep-coloured pink tourmalines can look almost red and are often called "rubellites"; these stones command much higher prices per carat than their lighter-coloured counterparts. Because of the way that pink tourmalines are generally orientated, this also allows for more oval and rounded cuts, compared to greens and blues.
Tourmaline may also be found with different colours in different parts of the crystal. Some gem deposits produce crystals that have one colour in the core of the crystal encircled by differently coloured layers. Such stones are often cut as slices with perhaps the most desirable being those with a pink core and a green rim - these produce stones known in the trade as "watermelon".
Other crystals may have different colours at different ends of the crystal, one end being green and the other pink, for example. The cutting of these stones is often the same as for many green and blue tourmalines with the table orientated to run along the length of the crystal to best attempt to make each colour as distinct as possible, preferably with each colour sharing similar proportions.
Stones that display two truly distinct colours in good proportion to each other are rare and are greatly desired by collectors.
Crystals with a greater number of inclusions are often cut into cabochon stones and, despite their inclusions, may still be attractive to buyers if they display vibrant colour. The relative affordability of rough as compared to some other varieties of gems means that carved stones, which require some wastage of material, are not that uncommon. Cat's eye tourmalines are rare but may also be found on the market.
The hardness of tourmaline sits between 7 - 7.5 on Moh's scale. Like other stones below an 8, it may not be a popular choice for an engagement ring; however, it is suitable for most other types of jewellery given a bit of care on the part of the wearer.
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