Glossary of Terms
Any mineral that falls under the following specifications belongs to the monoclinic crystal system:
Three axes, all of them are unequal in length. Two of them are at right angles to each other, while the third is lies at an angle other than 90°.
3D Animated Illustration of the Monoclinic System with Axes
Crystals kindly provided by Smorf
Monoclinic Selenite Crystal