Rock Crystal Classification
Refractive index, birefringence, optic character and optic figure. A bull's-eye optic figure is determinative for quartz; may also show Airy's spiral optic figure and Brazil-law twinning under crossed polarizing filters.
Colorless quartz with visible needle-like inclusions is a variety called "sagenitic." Stones with red hematite inclusions or "beetles-legs" may take a reddish appearance and be called "strawberry quartz." If colorless quartz contains golden blades of rutile it is often called "rutilated quartz."Misnomers: Herkimer diamond, Arizona diamond, Arkansas diamond, Alaska diamond, Cornish diamond. Rhinestones get their name from the rock crystal from the Rhine river that was cut and polished and used as diamond imitations.