Only one that occurs to me is "diatomaceous earth", deep deposits of tiny silicious remnants of diatoms. Very important industrially, as incredibly fine filter, e.g. to clarify beer. The "tom" part is not so obvious.
Webster's 1913 Dictionary

Definition: \Di"a*tom\, n. [Gr. ? cut in two. See {Diatomous}.]
1. (Bot.) One of the Diatomace[ae], a family of minute
unicellular Alg[ae] having a siliceous covering of great
delicacy, each individual multiplying by spontaneous
division. By some authors diatoms are called
Bacillari[ae], but this word is not in general use.

2. A particle or atom endowed with the vital principle.

The individual is nothing. He is no more than the
diatom, the bit of protoplasm. --Mrs. E. Lynn
Linton.