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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.