Tourmaline

Tourmaline is an igneous mineral that commonly forms in granites and granitic pegmatites, except for the brown magnesium rich dravite tourmaline, which forms in crystalline limestones. Tourmaline comes in a wide range of colors depending on its chemistry (which is very variable - see below). Some varieties of tourmaline are:

• Schorl - The most common variety of tourmaline, Schorl is the Fe-rich, black variety and mostly forms in pegmatites.
• Dravite - Dravite is the brown, Mg-rich tourmaline variety. It is less common than the other varieties and commonly forms in crystalline limestones.
• Elbaite - Along with liddicoatite, elbaite referrs to the Li-rich tourmalines. Elbaites are also rich in Na.
• Liddicoatite - Along with elbaite, liddicoatite refers to the Li-rich tourmalines. Liddicoatites are also rich in Ca.
• Verdelite - Verdelite is the Li-rich, green variety of tourmaline.
• Rubellite - Rubellite is the Li-rich, red-pink variety of tourmaline.
• Indicolite - Indicolite is the Li-rich, blue variety of tourmaline.
• Achroite - The rarer colorless/white tourmaline. This is not often found.

Tourmaline will commonly show several of the above varieties in a single crystal. This variation can be in layers along the length of the crystal or in concentric bands radiating from the long c-axis. These banded crystals are usually red/green and look like watermelon slices when cut giving rise to the name watermelon tourmaline.

Specimens: