sandstone vs gritstone

sandstone and gritstone both are nouns.

Word	Noun	Adjective	Verb	Adverb
sandstone	Yes	No	No	No
gritstone	Yes	No	No	No

As nouns, gritstone is a hyponym of sandstone; that is, gritstone is a word with a more specific, narrower meaning than sandstone:

sandstone: a sedimentary rock consisting of sand consolidated with some cement (clay or quartz etc.)
gritstone: a hard coarse-grained siliceous sandstone

Other hyponyms of sandstone include firestone, holystone, grit, gritrock, brownstone, bluestone, greensand, siltstone.

sandstone (noun)	gritstone (noun)
a sedimentary rock consisting of sand consolidated with some cement (clay or quartz etc.)	a hard coarse-grained siliceous sandstone