What is Tourmaline?
Tourmaline is a gemstone that is available in many different colours and falls under the cyclosilicate category of silicate minerals. Chemically, the tourmaline crystal is a boron silicate mineral compound that can have aluminium, iron, magnesium, sodium, lithium, and potassium present in it. The tourmaline stone was first discovered in Sri Lanka, and the Dutch East India Company mined large amounts of the tourmaline crystal and transported it back to their country.
The word tourmaline comes from the Sinhalese word “toramalli” which is a common term for reddish-brown semi-precious gemstones. Tourmaline colour varies greatly, and largely depends on its composing elements. Tourmaline colour is black, deep brown, or bluish-black if it is iron-rich. If it is a magnesium-rich tourmaline stone variety, then it might be brown or yellow. Sometimes, the tourmaline crystal can even be colourless.
Properties of Tourmaline
Depending on the tourmaline mineral, the stone can have many colours, such as blue, green, red, yellow, pink, etc. The tourmaline crystal can also be bi-coloured or multi-coloured, which is quite common. A special type of tourmaline stone, called watermelon tourmaline, has green on the outside and pink on the inside, resembling a watermelon. Some tourmaline varieties can also seem to have different colours when viewed from different directions. This phenomenon is called dichroism. The tourmaline colour can be altered by heat treatment. Heat-treating can lighten dark red stones. They can also be darkened irradiating with gamma rays. Manganese containing pale pink stones can be darkened to a great extent by this technique. However, heat-treated tourmalines are much less than untreated ones.
Tourmaline has the special property of pyroelectricity, which enables the stone to first attract and then repel hot ashes. When rubbed or heated, the tourmaline acquires an electric charge. Due to this special ability, the tourmaline mineral was nicknamed “ Ceylonese Sri Lankan magnet”. Since tourmalines are only slightly brittle, they are excellent for making jewellery.
Sources of Tourmaline
In the 1500s, Portuguese traders; in search of gold; obtained tourmaline from Brazilian indigenous people, and mistook it for emerald and sapphire. They took the stone back to their country and used it to make crown jewels and jewellery pieces for the royalty and the wealthy of the society. Today, Brazil is the largest producer of the tourmaline mineral. The Brazilian state of Minas Gerais has a rich deposit of pegmatite( an igneous rock), in which tourmaline is found. Several African countries also produce large quantities of tourmaline, such as Madagascar, Namibia, Mozambique, Tanzania, Nigeria, and Malawi.
In the United States, southern California is one of the leading producers of tourmaline. Since the 1800s, tourmaline has been the most important gemstone mined in California. Small amounts of tourmaline are also found in Sri Lanka, India, Pakistan, and Afghanistan.
Types of tourmalines
Tourmaline is a gemstone that has found wide usage in jewellery making due to its beautiful and varied colours. It is appreciated by both gem collectors and jewellery lovers for its vibrant appearance and appeal. Tourmalines are mainly of five species: schorl, uvite, dravite, liddicoatite, and elbaite. Of this, schorl or black tourmaline is most easily found.
Elbaite tourmaline, coloured bright green and bright blue due to the presence of copper, was found in Paraiba and Rio Grande do Norte, both states of Brazil in the 1990s. The Paraiba tourmaline is rare and very expensive. Similar variations were later found in Nigeria and Mozambique.
Black Tourmaline
Black tourmaline is also known as Schorl. Unlike other forms of tourmaline, schorl is never transparent or translucent. One of the most common forms of tourmaline, schorl forms in beautiful crystals and has high aesthetic value. It is one of the most lustrous black minerals found on Earth. In the Tourmalinated Quartz, schorl may form as tiny needles.
Schorl is most commonly found in granite pegmatites. It is usually brittle and found as heavily striated prismatic crystals. Its crystals may have a triangular cross-section. Fluor Schorl is a rare form of black tourmaline with a high quantity of fluorine.
The best quality schorls are mined in Shigar Valley and Stak Nala in Pakistan. Afghanistan, Namibia and Madagascar are also schorl producers. In Europe, schorl is produced by Italy, Portugal, the Czech Republic and Sweden.
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Benefits of Black Tourmaline
Schorl is very popular among gem collectors because of its beautiful lustre.
Schorl is used by jewellers as a black gemstone in jewellery.
Schorl-containing tourmalinated quartz is often used as a minor gemstone.
FAQs on Tourmaline
1.What is the composition of a tourmaline?
A large group of boron-silicate minerals are categorised under tourmaline. Varieties of tourmaline occur in various colours, due to varying chemical compositions. However, these crystals have the same physical properties and common crystal structure. Tourmaline occurs in pegmatite, an igneous rock. Tourmaline mineral contains sodium, calcium, aluminium, iron, magnesium, lithium and potassium impregnated in boron-silicate crystals.
Tourmaline is one of the most colourful mineral crystals found on Earth. The colour directly depends on the chemical composition of the particular crystal. Dark blue, black and deep brown tourmalines are usually iron-rich. Brown to yellow tourmalines are magnesium-rich, while lithium-containing tourmalines can be any colour, ranging from red, yellow or pink to green or blue. Bi-coloured tourmalines are also quite common, with the watermelon tourmaline being the most famous of the lot. Although rare, some tourmalines may contain copper, as in the case of Elbaite.
2.What are the types of tourmalines?
Some common types of tourmalines are:
Schorl: Most common type of stone, this variety is iron-rich.
Dravite: Brown tourmaline
Elbaite: Copper-rich tourmaline, this variety is most often used as gemstones due to their beautiful lustre. It is a native of Brazil.
Paraiba: Native to the Paraiba region of Brazil, this neon blue or green tourmaline variety is also highly desirable, and also frequently used as gemstones.
Indicolite: Dark to a light variety of tourmaline.
Rubellite: Red to Pink variety of tourmaline.
Cat’s Eye Tourmaline: Tourmaline that exhibits chatoyancy; also known as cat’s eye effect.
Watermelon Tourmaline: another highly desirable version of the stone, these varieties have green colour on the outside and pink on the inside.
