Tourmaline is one of the unique gemstones that can be found in all colours of the rainbow. This beautiful stone occurs in more colours and colour combinations than any other mineral group and can suit every taste and skin tone.
Tourmaline Origin and Formation
The name tourmaline comes from the Sinhalese word “turamali” which means “stone with various colours”. In fact, “tourmaline” is the name of a large group of boron silicate minerals, which have a common crystal structure and similar physical properties but vary in chemical composition.
Tourmaline family includes the following main varieties: dravite, uvite, elbaite, liddicoatite and schorl, the latter being the most common variety making up nearly 95% of all tourmaline deposits. However, most tourmalines used for jewellery manufacturing belong to elbaite group.
Since tourmalines have a large variety of colours, they are usually traded under colour-specific names. For example, pink-red stones are called “rubellite”, blue-green “Paraiba”, blue “indicolite” and multicoloured ones are called “watermelon tourmalines”. Descriptive names such as “yellow tourmaline” or “pink tourmaline” are also used for fancy-coloured gemstones.
Tourmalines have very good hardness 7 – 7.5 on the Mohs scale and are found in pegmatites and alluvial deposits all over the world.
Being the national gemstone for the United States, it has been mainly mined in the US up until the early 1900s. Today, the most significant sources are Brazil, Bahia and Minas Gerais. Tourmaline deposits can also be found in Afganistan, Burma, India, Italy, Madagascar, Mozambique, Namibia, Nepal, Russia, Pakistan, Nigeria, Sri Lanka, Tanzania, Zimbabwe, Zambia and Zaire.
Zambia is known for fine red rubellite and canary yellow tourmalines, Afganistan is producing fine green verdelite and rare blue indicolite. While Nigeria and Mozambique are famous for producing Paraiba tourmalines.
Tourmalines occur in a wide range of colours and shades from colourless to black. Colourless ones are considered to be the rarest variety but they are also the least valuable. While the most common tourmaline colour is black (Schorl tourmalines).
Most tourmalines display two ore more colours in a single stone or two shades of the same colour. The variety of tourmalines that exhibit green on one end and pink-red on the other are called “watermelon tourmalines”.
One of the most sought-after colour is the pink/red variety which is called rubellite.
Most green tourmalines exhibit strong pleochroism which is the ability of the crystals to show different colours (bright green in one direction and blue in another) depending on the angle from which they are viewed. Such stones are the most valuable.
Dark-toned green stones, which are more common in the marketplace, can appear almost black from certain angles. These stones are described as “oily” or “olive” green.
Blue tourmalines can range in colour from light to dark tones. The shade is often modified by green so you can see blue colour with a bit of green or very greenish-blue.
Paraiba tourmalines appear in a wide range of greenish-blue, bluish-green, green, blue and violet shades. There are many terms to describe the quality of Paraiba tourmalines, such as “electric”, “turquoise”, “sapphire“, “mint” green and “tanzanite” blue. Because of the high value of the rough, Paraiba tourmalines are almost always custom cut.
Because of the environment tourmalines grow, they are often included. The level of inclusions typically depends on the type of gemstones, meaning some colours are more included than others.
Green tourmalines are often eye-clean, while blue, rubellite, Paraiba and watermelon tourmalines are almost always found with visible inclusions.
Inclusions are much more visible in light tone stones. Such tourmalines are usually cut into cabochons to emphasize the colour and hide the flaws.
As a general rule, the more visible any inclusions are, the less the stone costs.
Because of the elongated crystal shape, tourmalines are often cut into long rectangular bars. However, these gemstones also come in many traditional and fancy shapes.
Since tourmalines can exhibit different shades under certain angles, cutters may orient a gem based on the depth of colour. For example, to darken light rough, they orient the table perpendicular to the crystal’s length. To lighten the dark shade, they orient gem’s table parallel to the crystal’s length.
Tourmaline Carat Weight
The price per carat of large size tourmalines is considerably high. However, it’s worth mentioning that these spectacular sizes are very rare. In general, the price per carat increases significantly as the gem pass the 5-carat milestone.
As a general rule, it’s recommended to buy coloured gemstones such as tourmalines by size and not by carat weight. Tourmalines vary in size to weight ratio, so some stones look larger while others look smaller but have greater carat weight in comparison.