Many to most of the citrines on the market today are heated amethysts. Naturally occurring citrines are a rich yellow to almost orange color, and very rare. Both stones are in the Quartz family. Amethyst turns yellow when heated.

Other quartz family stones include chalcedonies, onxy, bloodstone, tiger's eye, smokey and rose quartz, and ametrines too.

The corundum family is sapphire and ruby. The beryl family of gemstones is composed of emerald, aquamarine, morganite, heliodor, goshenite, and the rare bixbite (red beryl). These are some of the most valued of all colored gemstones.

I have a HUGE Amethyst cabochon ring with pink tourmalines on the side, and it's to die for.
You just don't see perfect cabochons anymore