In the monoclinic system all the axes are different lengths. Two of them, the A and the C axes, meet at 90 degrees but the third one does not.
This crystal system has the following forms:
- 3 Pinacoids
- Prism and 2 Pinacoids
- Prism and 3 Pinacoids
- Prism and 5 Pinacoids

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Pinacoid: A pinacoid is composed of only two parallel faces. In this case, the top and bottom face are the pinacoid forms (the blue faces). There are a total of three pinacoids in this form.
Diagrams originally from http://library.thinkquest.org/C005277/Crystal.html