volcanic glass vs volcanic rock

volcanic glass and volcanic rock both are nouns.

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

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

volcanic glass: a kind of natural glass produced when molten lava cools very rapidly
volcanic rock: extrusive igneous rock solidified near or on the surface of the Earth

volcanic glass (noun)	volcanic rock (noun)
a kind of natural glass produced when molten lava cools very rapidly	extrusive igneous rock solidified near or on the surface of the Earth