Assertion: mineral's crystal | /r/HasProperty | mineral
Facets:
Source sentences:
text: Not all naturally occurring crystals are minerals either; opal and amber, the sap of ancient trees that have fossilized, are not minerals.
text: Quartz crystal is one of several minerals which are piezoelectric, meaning that when pressure is applied to quartz, a positive electrical charge is created at one end of the crystal and a negative electrical charge is created at the other.