Topaz
The name is believed to come from 'topazos' - 'seek/hard to find'.
This name, "Topazos" was originally used to name the mineral we now know as Peridot. The first peridot gems came from 'Topazos' island, now called 'Zeberget' island in the Red Sea. It was a difficult island to find and very protected.
Topaz is an allochromatic gem, which means that its color is given by certain elements outside its formula that were introduced into the crystal lattice during its formation. In its pure form it would be colorless.
Al2SiO4(OH,F)2