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Earth Measure: Native American Geometry Designs: Mathematical Landscaping
If you want to plant a class garden, this is a great resource for combining geometry, Native American studies, and rocks.
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Finite Geometry Notes: Diamond 16 Symmetry Puzzle
At this site see if you can solve the "Diamond 16" puzzle. Change the patterns to create ordinary or color exchange symmetry. This is just one of several challenging puzzles at this site. Links to similar puzzles and games.