In ancient times, just about any yellow gem was likely to be called topaz. The name itself may have been derived from a Sanskrit word meaning 'fire'.
The most important color variety of topaz is the range of yellow and brown gems. Golden-brown topaz is the most expensive color variety, with large faceted gems commanding prices of several hunderd dollars per carat.
Topaz, from any sources, is reasonably clean. The exception is with pink and red topaz, where only small stones are usually available. In these stones, slight inclusions are tolerated.
Topaz is very hard, at 8 on the Mohs scale, it wears well in jewelry.