Rocksday

Tourmaline

A boron-bearing silicate found in more colors than almost any other gem. Black schorl is the most common form.

Tourmaline specimen
Photo: Robert M. Lavinsky, CC BY-SA 3.0, via Wikimedia Commons

How to identify tourmaline

  • Long prisms with lengthwise grooves (striations).
  • Rounded-triangle cross-section when broken across.
  • Hard — scratches glass.
  • Gem crystals can change color from end to end ('watermelon').

Often confused with

Where it's found

  • Mount Mica, Maine
  • San Diego County, California
  • Minas Gerais, Brazil
  • Afghanistan

Uses

Gemstones; historically pressure gauges thanks to its piezoelectricity.

Rock tumbling

Great for tumbling.

Did you know?

Heated tourmaline becomes electrically charged — Dutch traders used it to pull ash from their pipes.

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