…and half a dozen of the otherThis site about igneous rocks, rocks. (Was that a bit too corny and contrived? Yep, thought so…)
Anyhow, that page also contains links to other bits of the site where you can find out about sedimentary and metamorphic rocks too.
After reading this page about brickwork patterns, I’ll never look at a brick wall in quite the same way again. [via Wikipedia’s equally fascinating brickwork page.]
Phil’s Tree Pages. Excellent site.