Tourmaline

Tourmaline gisements

Fluorite-Foitite-Schorl-k-117a

Tourmaline noire ou Schorl

Black Dravite, Yinnietherra, Western Australia

Elbaite-Lepidolite-Quartz-gem7-x1a

Elbaite with albite - São José da Safira, Minas Gerais, Brazil

Tourmaline is a crystalline boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and comes in a wide variety of colors.

Etymology

The name tourmaline comes from the Sinhalese term turmali, which was used to refer to colored gemstones found in Sri Lanka. This term was anglicized to tourmaline in the early 18th century.

Properties

Tourmaline belongs to the trigonal crystal system and is distinguished by its three-sided prisms; no other common mineral has three sides. The most common species of tourmaline is Schorl, which accounts for ninety-five percent of all tourmaline in nature. The crystal structure of tourmaline is hexagonal, making it unique among minerals. Its hardness is 7-7.5 on the Mohs scale of mineral hardness, making it durable enough for various types of jewelry.

Tourmaline is piezoelectric and pyroelectric, which means it can generate an electric charge under pressure or when heated. These properties have led to its use in pressure measuring instruments and in temperature gradient applications.

Color Varieties

Tourmaline exhibits a wide range of colors, from black to bluish-black, dark brown, yellow, medium brown, blue to neon blue, lime to dark forest green, red and reddish purple, yellow, pink, and colorless. The color variations can be attributed to trace amounts of different elements such as iron, manganese, chrome, and vanadium. Some tourmaline specimens are bi-colored or tri-colored, and are highly prized for their unique beauty. The most expensive and desirable color is the neon blue variety from Paraiba, Brazil, known as Paraiba Tourmaline.

Geological Occurrence

Tourmaline is found in pegmatite and metamorphic rocks worldwide. Significant deposits have been discovered in Brazil, Sri Lanka, Africa (Nigeria, Tanzania, Kenya, Madagascar, Mozambique), and the United States (California and Maine). The diversity in the geological environments that can produce tourmaline results in the wide variety of colors and compositions seen in this mineral.

Uses

Beyond its use as a gemstone in jewelry, tourmaline is employed in a variety of industrial applications due to its piezoelectric and pyroelectric properties. It is used in high-pressure gauges, polarizing filters for optical applications, and as a component in electrical and electronic equipment.

Cultural Significance

Tourmaline is believed to have metaphysical properties, with different colors of tourmaline said to have different healing properties. It is considered a stone that promotes self-confidence and diminishes fear. Tourmaline is also the birthstone for October.

See Also

• Gemstone
• Mineral
• Piezoelectricity
• Pyroelectricity

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