Assertion: chalcedony's hardness | /r/HasProperty | specific gravity of 2.59
Facets:
Source sentences:
text: Like other chalcedony quartz gemstones , fire agate has a hardness of 6.5 to 7 on the Mohs scale; a specific gravity of 2.59 to 2.67; and a refractive index of 1.530 to 1.540.