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Tourmaline is a group of minerals that are known for their vibrant colors and hardness. It's a borosilicate mineral that forms in long, prismatic crystals with a triangular cross-section.

Physical properties

• Hardness: 7–7.5 on the Mohs scale, making it hard enough to be used as a gemstone

• Crystal structure: Trigonal, with a six-member ring cyclosilicate structure

• Shape: Long, prismatic crystals with a triangular cross-section

• Cleavage: Indistinct

• Fracture: Conchoidal, sometimes forming spherical lumps

• Specific gravity: 3.0–3.12, varying with color

• Pleochroism: Strong, visible to the naked eye, and varies with color

Color

• Tourmaline can be found in many colors, including black, blue, green, yellow, pink, red, orange, purple, and brown

• Some tourmalines have a cat's-eye effect called chatoyancy

• Some tourmalines are zoned with a combination of colors

Uses Tourmaline is often cut into gemstones and Tourmaline can be used for carving.

Examples of tourmaline

• Elbaite: A variety of tourmaline that is often transparent and colorful

• Schorl: An iron tourmaline that is black in color

• Dravite: A magnesium tourmaline that is brown in color

• Rubellite: A pink alkali tourmaline

• Brazilian emerald: A green alkali tourmaline

• Achroite: A colorless alkali tourmaline