Assertion: obsidian | /r/HasProperty | glass
Facets:
Source sentences:
text: As obsidian is a glass and cristobalite is a crystal, snowflake obsidian is essentially a lot of tiny crystals trapped in black glass rock.
text: This is because obsidian is glass and has no crystal structure, whereas metals are limited to the structure of their crystal boundaries.
text: Your Swiss army knife is made of metal, so it can only be sharpened down to the size of its molecules, but because obsidian is glass, it has no crystal structure.