Assertion: obsidian | /r/MadeOf | silica
Facets:
value: is due to the fact
type: CAUSE
value: unlike black tourmaline
type: OTHER
value: primarily
type: DEGREE
Source sentences:
text: Obsidian is primarily made of silica, not unlike black tourmaline, but due to the fact that the obsidian forms quickly from the cooling lava, there is no time for a crystalline structure to form, resulting in the amorphous black glass called obsidian.