21 C.F.R. § 573.340
Diatomaceous earth
(a) Identity. The additive consists of siliceous skeletal material derived from various species of diatoms.
(b) Specifications. The additive shall conform to the following specifications:
(c) Uses. It is used or intended for use as an inert carrier or anticaking agent in animal feeds in an amount not to exceed 2 percent by weight of the total ration.