sandstone vs siltstone

sandstone and siltstone both are nouns.

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

As nouns, siltstone is a hyponym of sandstone; that is, siltstone 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.)
siltstone: a fine-grained sandstone of consolidated silt

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

sandstone (noun)	siltstone (noun)
a sedimentary rock consisting of sand consolidated with some cement (clay or quartz etc.)	a fine-grained sandstone of consolidated silt