You can find various websites discussing the crystal systems (see my short list below), but in all honesty, the best way to mastering these systems is to deal with them in 3D.
Print out these sheets and build your own unit cells (the building blocks of a crystal) to get a 3D, tactile representation of how the systems work. Write down the relevant information (such as the name and the angle and length relationships) on each crystal. Rotate them to get an understanding of their symmetry.
To increase durability, I pasted my print-outs onto cereal boxes and then cut them out and folded them, using clear packing tape to keep the sides together (see my photo to the right).
- VIDEO LECTURES: Dr. Haywick of the University of Southern Alabama has shared lectures from his crystallography and mineralogy course on YouTube (27 videos, ~0.5-1 hr each).
- As always, Wikipedia is a good place to start.
- The University of Liverpool has a flash animation that visually shows how the crystal systems relate to each other. Their pages feature simple, easy-to-understand paragraphs . Click "Next" and "Previous" to navigate through their topics.
- If you're looking to see which minerals fall into which system, check out CrystalAge.
- AllAboutGemstones has good images of actual minerals crystallizing into system shapes (used above).
- Boomeria also has photos of which minerals fall into, in addition to visual slides on crystallography.