- Home
- Rocks
- Type fossils
- Fossil Specimens
- Minerals
- Glossary
- Stratigraphic Chart
- Michel-Levy Chart
- Classification of igneous rocks
- University of Cambridge
- Department of Earth Sciences
- ESC Library
- Moodle
- Sedgwick Museum
- DoITPoMS
- Mindat.org
- Microfossils
- Bryozoans
- Webmineral
- Tree of Life
- CrystalMaker
- Virtual Microscope
Tourmaline
Title
Tourmaline
Subject
Tourmaline is the only common mineral of which boron is an essential constituent. Its presence in a rock, therefore, indicates that the rock contains significant boron.
Description
Formula
(Na,Ca)(Mg,Fe,Mn,Li,Al)3(Al,Mg,Fe3+)6[Si6O18](BO3)3(O,OH)3(OH,F)
Structure
Ring silicate
Crystal System
Crystal system: trigonal (-)
Physical Properties
Colour in hand specimen: black
Hardness: 7
Optical Properties
Colour in plane polarised light: typically brown-green or green
Pleochroism: strongly pleochroic in many colours
Relief: moderate
Birefringence: typically 2nd order
Rock Specimens
Mineral Name
tourmaline
Citation
“Tourmaline,” 1A Collections, accessed April 9, 2024, https://wserv3.esc.cam.ac.uk/p1acollections/items/show/47.