Assertion: black obsidian | /r/ObjectUse | used as the backing
Facets:
value: for opal doublets
type: TRANSITIVE-OBJECT
value: often
type: TEMPORAL
value: for triplets
type: TRANSITIVE-OBJECT
Source sentences:
text: Not only can obsidian be carved into decorative shapes to ornament the home and made into beads and cabochons, but light green and yellow material from Peru can be faceted and black obsidian is also often used as the “backing” for opal doublets and triplets.