Crystals along with small rocks are permitted in checked or carryon baggage. This is per TSA website. Simply enter the name of the item you wish to take with you.
There is, essentially, no such thing as a "permitted" item, due to TSA's CYA language on their web page:
Planning ahead and packing properly can facilitate the screening process and ease your travel experience at the airport. Know what you can pack in your carry-on and checked baggage before arriving at the airport by reviewing the lists below. Even if an item is generally permitted, it may be subject to additional screening or not allowed through the checkpoint if it triggers an alarm during the screening process, appears to have been tampered with, or poses other security concerns. Read about civil penalties for prohibited items.
The final decision rests with the TSA officer on whether an item is allowed through the checkpoint.
Notice the bolding (which is mine). The TSA officer can deny you anything he decides to deny you.