crystal vs natural glass

crystal and natural glass both are nouns.

Word	Noun	Adjective	Verb	Adverb
crystal	Yes	No	No	No
natural glass	Yes	No	No	No

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

crystal (noun)	natural glass (noun)
a protective cover that protects the face of a watch	magma of any composition that cooled very rapidly
glassware made of quartz
a crystalline element used as a component in various electronic devices
a rock formed by the solidification of a substance; has regularly repeating internal structure; external plane faces
a solid formed by the solidification of a chemical and having a highly regular atomic structure
colorless glass made of almost pure silica