Random post, but I saw this on a makeup blog and had to try it. My MAC eyeshadow cracked and I thought it was doomed forever.
All I did was add a couple drops of rubbing alcohol, mixed it slightly with a tweezer, and then stamped it with the top of my nailpolish. Voila!
Then I took my ol' trusty big fatty mascara, which was a bit dried out, added a few drops of eye drops, and it was nice and fluid again!