clastic rock vs clastic

clastic rock is a noun but clastic is not a noun.

Word	Noun	Adjective	Verb	Adverb
clastic rock	Yes	No	No	No
clastic	No	Yes	No	No

clastic rock (noun)	clastic (noun)
(geology) a rock composed of broken pieces of older rocks

clastic rock (adjective)	clastic (adjective)
	capable of being taken apart
	of or belonging to or being a rock composed of fragments of older rocks (e.g., conglomerates or sandstone)