Assertion: obsidian | /r/MadeOf | 4 to 10 percent
Facets:
value: generally
type: DEGREE
value: by weight
type: OTHER
Source sentences:
text: Pitchstone is richer in water than are obsidian and most other glassy rocks, generally containing 4 to 10 percent by weight; most of this water may have been absorbed from the sea or wet sediments into which the pitchstone was intruded.