I got a few of these with each one having a different crystal. 
Each one consists of an aluminum tower 1" wide topped with what looks like gold plated copper vanadate mounts that are typically used in Verdi lasers. 
 
These crystal mounts are all tec cooled or water cooled and appear to be testing towers for various crystals

They could be any crystal that is non hygroscopic as these have been in the air and show no damage from humidity.

This one is water cooled and appears to be vanadate by the coloration but not sure, it has a red/pink colored anti reflection coating on both ends.




I combine ship to keep costs down.