Topaz is thought to first originate from the legendary island of Topazios, off the coast of Egypt now known as Zebirget. Topaz occurs in a variety of colors, with natural sherry topaz and pink topaz being the most valuable. Most pink topaz on the market is yellow topaz that has been heat treated. Deep blue topaz - often called London topaz - has been irradiated. Both effects are permanent and deemed harmless. (There was a question about lingering radiation, but this has not been supported by testing.) Russia, Brazil and Nigeria are major sources of topaz, but it is found across the globe. Topaz is formed by fluorite bearing vapors given off in the last stages of crystallization in various igneous rocks, including rhyolite and pegmatite dikes.
Zircon takes its name from the Arabic zargun, meaning "gold color". It's been mined for over 2000 years in the alluvial gem deposits in Sri Lanka and used as a gemstone in Greece and Italy. It's found in a variety of colors: colorless, red, golden yellow, green and blue. Heat-treating brown zircon into blue-zircon has been practiced for centuries; stones were placed in clay pots with fine sand and heated in the coals of a campfire. Blue zircon reheated becomes golden yellow and may be the source of the ancient name.