The basics
So what is tourmaline, really?
Tourmaline isn't one mineral. It's a group of boron silicates that grow as long, stripy columns.
Black tourmaline, called schorl, is by far the most common kind. Most green, pink and blue ones are elbaite. When a crystal grows pink inside and green outside, it's called watermelon tourmaline.
Heat or squeeze a crystal and its two ends pick up opposite electric charges. Geologists call that pyroelectric and piezoelectric.


