bi-color tourmaline – Joopy Gems

Joopy Gems Bi-Colour Tourmaline Polki mix

John Ruskin said, ‘The making of tourmaline is more like a medieval doctor’s prescription than the making of a respectable mineral’. This refers to the extraordinary colour range of tourmaline, completely unparalleled, which amusingly does not necessarily relate to the chemical composition. Yes, that’s correct; there is no simple relationship between composition and colour! And tourmaline stones are named more for their colour than their composition. It’s complicated, but lets break it down a bit.

MJS Jewellery Design Chrome Tourmaline Ring

The name comes from the Sinhalese word ‘toromalli’ meaning ‘mixed gems’, a term that the Dutch merchants in Sri Lanka applied to the rough, water-worn pebbles found in the gem gravels. It has been routinely confused with other gems; emerald, ruby for example, and it wasn’t until a few centuries after the first stone had been discovered, and confused with emerald, that it was recognised as a separate species. It is small differences in chemical composition that give tourmaline its differing colours. If you look at tourmaline as being a collection of related mineral species that have the same crystal structure but slightly differing chemical and physical properties, that helps to explain. They are all silicates – silicates being compositions of silicon and oxygen, and making up some 95% of the earth’s minerals, so very common. They all share certain elements – fluorine, boron, aluminium, but contain differing levels of other elements: sodium, lithium, calcium, magnesium, manganese, titanium, copper, and iron.

A tourmaline’s chemical and physical properties are used to define its species: elbaite, liddicoatite,
dravite, uvite, and schorl. However, each species will demonstrate a variety of colours. So you can’t say elbaite is pink, liddicoatite green and so on, although schorl is always black. This is what I mean when I say that tourmaline is referred to by colour rather than species. So intense hot pink tourmaline is called rubellite, blue to teal is called indicolite, green tourmaline is verdelite and paraiba is an intense neon turquoise, named for the state in which the gem producing mine was found.

Tomfoolery London One of a Kind Tourmaline Ring — Vram Jewelry Yellow Tourmaline Ring

The most fascinating, though, for me is the parti-colour and bi-colour stones. This tends to happen with the liddicoatite species, and it occurs when the trace elements change in either concentration or composition during the crystal’s growth. This can give rise to really striking patterns, and these stones can be cut as slices if the colour zoning occurs parallel to the length of the stone, familiarly known as ‘watermelon’ tourmaline. This term was coined for those stones with the bright pink interior and green rim, but can and is used for any slice with particolour characteristics. Alternatively the zoning can take place across the length of the stone which gives the half and half effect on a long crystal. Another very valuable type of tourmaline is known as chrome tourmaline, and this is a very vibrant green colour, and this is of either the dravite or uvite species, or a combination of both. Whilst these normally produce yellow to brown coloured crystals, when vanadium or chromium is present, they will come up bright green.

Because tourmaline crystals tend to grow long and narrow, with those very distinctive striations down the sides, you often find them in very non-standard sizes and they can be harder to find in more familiar, calibrated forms. You can only really cut them along the length as the stones tend to be dead down the length, or in very thin slices. Tourmaline is extremely strongly pleochroic, and one colour is typically much darker than the other. When you consider also that tourmaline absorbs more light down the length of the stone rather than across the width, a crystal that appears, say, light green across the width of the stone may well appear almost black down the length.

Julia Lloyd George Modern Art Tourmaline Earring

Pala International Paraiba Tourmaline Pear — Julia Lloyd George Modern Art Tourmaline Earring

You can also get chatoyant tourmaline, although the fibres are relatively coarse, and tourminalted quartz. Schorl is not used much these days but was popular in Victorian times as mourning jewellery, as it was a great deal tougher than jet. As always, to shop my tourmaline, click here

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Watermelon tourmalines classically mimic the fruit, with their juicy fruit and rind; bright pink in the middle, green on the outside. However, they come in so many different colours, representing the full spectrum of tourmaline’s impressive colour range. In fact tourmaline’s original name was ‘turamali’ which means ‘mixed colours’. It’s quite simply one of my favourite stones, but maybe not the easiest to set; it’s not always easy to find pairs and the profiles are often very uneven and bockety.

Tourmaline grows in pegmatites – veins that run through rocks created by molten magma from volcanoes. As the magma cools, cracks form which fill with a solution of water and minerals such as iron, lithium or manganese. Over thousands of years, these turn into tourmaline crystals, and it is depending on which of these minerals is present that determines the colour. So how do you end up with more than one colour in the same stone? This happens when the trace elements change in concentration or composition during a crystal’s growth. This can result in a core of one colour and bands of different colours, or zones across the length of the crystal. A single tourmaline crystal can contain up to 15 different colours. Tourmaline is the birthstone for October and I always think that is so lucky, as you have such a huge choice of colours. It is said to be particularly beneficial to artists and those in creative fields.

Watermelon tourmaline lends itself wonderfully to carvings – in particular butterfly wings and leaves look great, but arguably the best way to display it is quite simply, in slices, to show off its saturated juiciness to full effect. Although it can be prong-set, I love to see these slices in bezels. I always think of India Mahon as the absolute queen of tourmaline, and I also especially love Sarah Walker’s classic settings below. I haven’t seen slices set like this very often and I really like it. Links and titles on each photo.