You can obtain Topaz Gypsum by defeating creatures level 55+ while under the effect of Topaz Gypsum Attunement Potion.
Cooldown
Drop Quantity Limit: 10
Time Between Drops: 0
Limit Expiration: 18h
Note: the drop counts towards the limit as soon as it is on the ground (when a loot bag drops). If you do not pick it up, you will miss one gypsum until the limit expires.