Yellow To Yellowish Orange
refractive index, birefringence, optic character and optic figure. A bull's-eye optic figure is determinative for quartz. Might also show Airy's spiral. Careful observation that reveals Brazil-law twinning separates citrine from scapolite with similar properties.
Citrine is the common variety name for transparent quartz with a predominantly yellow to orange body color. Stones might be piezoelectric: able to generate electricity produced by mechanical pressure, Pyroelectricity: development of opposite charges at the ends of the axis due to change in temperature and triboluminescent: luminescence produced by friction. Misnomers: topaz quartz, Spanish topaz, Saxon topaz, Madeira topaz, citrine topaz, topaz quartz.