green to yellowish green
green quartz, "greened amethyst"
Refractive index, birefringence, optic character and optic figure. A bull's-eye optic figure is determinative for quartz. The presence of Brazil-law twinning is a means of separating amethyst from scapolite.
Misnomer: green amethyst. Green color is rarely found naturally and most are irradiated and/or heat treated.