Perhaps slight alterations in temperature and pressure caused the clumping? In any manner, it should be good to smoke. I'm not exactly sure how one could tell that it's "not good" anymore just from examining the crystals, but it seems that even if they did "expire", the most likely case would simply be that they wouldn't be as potent as they would have been, but that doesn't seem like a terrible consequence for trying it out.
"Science without religion is lame. Religion without science is blind" - Albert Einstein
"The Mighty One appears, the horizon shines. Atum appears on the smell of his censing, the Sunshine- god has risen in the sky, the Mansion of the pyramidion is in joy and all its inmates are assembled, a voice calls out within the shrine, shouting reverberates around the Netherworld." - Egyptian Book of the Dead
"Man fears time, but time fears the Pyramids" - 9th century Arab proverb