Assertion: onyx's layer | /r/HasProperty | thin upper
Facets:
value: very
type: DEGREE
Source sentences:
text: Some varieties of onyx differ in color, such as sard onyx, which has a brown base and white upper layer, cornelian onyx, which has a red base and white upper layer, and niccolo onyx, which has a very thin upper layer, allowing the black base color to show through as grey or blue.