Assertion: opal | /r/CapableOf | occur as thin seams of material
Facets:
value: within a host or matrix rock
type: LOCATION
value: frequently
type: TEMPORAL
Source sentences:
text: Because opal frequently occurs as thin seams of material within a host or matrix rock, some deposits are cracked or are so thin and fragile that they are not suitable for stand-alone jewellery.