Tourmaline: Rainbow Gem
Tourmaline is the alternative to opal as birthstone for October and offers a beautiful rainbow of colourful gems to choose from. No other gemstone has quite the range of colours that tourmaline does with a huge variety of shades and hues, and even stones that have more than one colour!
Tourmaline was recognised as a mineral species in the 1800s. Before this it was often confused with other gems. For instance, when green tourmaline crystals were first discovered in Brazil in the 1500s they were thought to be emeralds. The name tourmaline originated in Sri Lanka and comes from the Sinhalese meaning ‘mixed gems’ which refers to the multi-coloured assortment of crystals found in the gem gravels of that country.
You will often find tourmaline sold using a colour prefix such as pink or green tourmaline, but some varieties have their own names. Rubellite is the name given to red tourmaline although it is often also used for stones with a reddish-pink colour too; the point at which pink becomes red is difficult to establish, often depending on how exactly the observer perceives colour. Tourmaline also has strong pleochroism, a property that is connected to the way light interacts with a gemstone. In tourmaline’s case it means the gem can appear different colours when viewed from different directions, often darker and lighter shades of the same colour.
Blue tourmalines including those that are violetish-blue or greenish-blue are known as indicolite. A rare variety with a vivid blue to green colour is Paraiba tourmaline. This was first discovered in the state of Paraiba in Brazil although the name is often now applied to similar gems from Mozambique and Nigeria. They receive their colour from the presence of traces of copper which gives a stunning brightness to their colour. Paraiba tourmaline is rare and can fetch very high prices for fine quality stones.
Although green is a reasonably common colour for tourmaline, some stones have an especially bright hue that can look like fine Tsavorite or emerald. These stones are known as chrome tourmaline although many of them actually receive their colour from traces of vanadium within the crystal rather than chromium!
It is not uncommon for a single tourmaline crystal to display more than one colour due to alterations in conditions during crystal growth. The crystals form as long prisms with a rounded triangular cross-section and those displaying more than one colour may vary along the length (so one end of the crystal is one colour and the other end a different colour) or have concentric zones of different colours when viewed in cross-section. Because of the range of colours seen in tourmaline it is possible to see a wide variety of combinations, but the most common is green and pink. A variety called watermelon tourmaline is often cut into slices to display a pink centre framed by an outer zone of green.
Tourmaline has a reasonable level of hardness and can be worn regularly, but it does require quite frequent cleaning. This is because it is both pyroelectric and piezoelectric. The first of these properties means it becomes electrically charged when heated while the second means it becomes electrically charged when put under mechanical stress (e.g. squeezed). The charge can cause the gem to attract small particles like dust, especially when it is displayed under a jeweller’s bright, hot lights!
If you would like to learn more about tourmaline or view our tourmaline jewellery please visit our showroom, where our team of jewellers and gemmologists will be happy to help. You can also view some of our tourmaline jewellery on our website.
Comments on this post (0)