biolith

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A rock formed from the remains of or physiologic action of organisms.

from The Century Dictionary.

• noun In petrography, a term proposed by Ehrenberg as a general name for a rock composed exclusively of organic debris. Also organo-lith.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geology A rock or other geological feature formed by living organisms.