Characteristics of Tourmaline:

Chemical Name: Complex boron silicate

Formula: NaFe ²⁺ ₃Al ₆(Si ₆O ₁₈)(BO ₃) ₃(OH) ₃(OH)

Colors: Various

Structure: Trigonal

Hardness: 7-7.5

Specific Gravity: 2.8-3.3

Refractive Index: 1.61-1.67

Lustre: Vitreous

Streak: White

Locations: USA, Brazil, Czech Republic, Italy, Nigeria, Namibia, Madagascar

What is Tourmaline? 

Tourmaline refers to a family of borosilicate minerals of variable composition, but all with the same basic crystal structure. There are more than 30 minerals species in the Tourmaline group, including elbaite, dravite, and schorl. However, while mineral names are based on chemistry, gemstone names are based on color and take no notice of Tourmaline species. These include indicolite (blue), achroite (colorless) and rubellite (pink or red). The crystals generally form pencil-like prisms, with a rounded-triangular cross-section, and unlike the rocks in which they often form, Tourmaline minerals are resistant to weathering. As a result, they tend to accumulate in gravel deposits; the origin of the name is the Singhalese word turmali – “gem pebbles”.

Variety of colors

There is no simple correlation between chemical composition and color. Most gemstone Tourmaline material comes from the species elbaite, which is usually green, although it can occur in many other colors. Emerald green is fairly rare and thus valuable. Until the 18^th century, it was often confused with emerald. The most dramatic Tourmalines are the color-zoned gems called “watermelon” Tourmaline; when sliced across the crystals, this variety shows a red or pink center surrounded by a rim of green. The deepest color is always seen when looking down the length of the crystal, so it is important to position rough material correctly when cutting gems.