I got in my stocking a really cool clear Calcite crystal, and an amazing Bismuth crystal! I have never seen or heard of these before, they are so awesome! Here's a pic I got from amazingrust.com. My sample looks just like this on the bottom. On top it's like a cluster of pyramids that are beautifully colored.
Isn't that cool!? The outsides of the crystal grow faster than the insides, making it a hollow square spiral. The metal oxidizes on the outside which is what gives it the coloring. (Read more about it at http://amazingrust.com/experiments/how_to/Bismuth_Crystals.html).