lava vs volcanic rock

lava and volcanic rock both are nouns.

Word	Noun	Adjective	Verb	Adverb
lava	Yes	No	No	No
volcanic rock	Yes	No	No	No

As nouns, volcanic rock is a hypernym of lava; that is, volcanic rock is a word with a broader meaning than lava:

lava: rock that in its molten form (as magma) issues from volcanoes; lava is what magma is called when it reaches the surface
volcanic rock: extrusive igneous rock solidified near or on the surface of the Earth

lava (noun)	volcanic rock (noun)
rock that in its molten form (as magma) issues from volcanoes; lava is what magma is called when it reaches the surface	extrusive igneous rock solidified near or on the surface of the Earth