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Tourmaline is a group of minerals that are hard enough to be used as gemstones. It's known for its many colors, including pink, blue, green, yellow, red, orange, purple, brown, and colorless.

Physical properties

Hardness: 7–7.5 on the Mohs scale

Crystal structure: Trigonal, with rounded triangular cross-sections

Cleavage: Indistinct

Fracture: Conchoidal, sometimes forming spherical lumps

Specific gravity: 2.8–3.3, depending on chemical composition

Color

Black: The most common color

Zoned: Some tourmalines have different colors in different parts of the crystal

Cat's-eye effect: Some tourmalines have a chatoyancy effect, caused by thin inclusions that form during growth

Types

Iron tourmaline: Also known as schorl, this type is black

Magnesium tourmaline: Also known as dravite, this type is brown

Alkali tourmaline: This type can be pink (rubellite), green (Brazilian emerald), or colorless (achroite)

Uses Cut into gemstones and Carved into decorative objects.