Quartz and topaz look very different
,Topaz has a very different refractive index,
You can use a refractometer, but should be able to tell by eye, Quartz has a nice sparkle but Topaz often reflects yellows and blues like a diamond, that is why it is described as silver at times, the shine and sparkle are totally different from quartz.
Most quartz is normally just translucent and may have some sparkle but Topaz has been used as a substitute for diamonds for many years.
I do advise the Refractometer is the best tool for those who can not tell by just looking at the gem. I can understand when you deal with particular gems all the time, When you take your colored gems or Gemologist courses you learn those things and most of all experience,
Place some nice high quality topaz beside some translucent quartz, I am sure he will be able to tell the difference, The eye will catch those beautiful colors irradiate from the topaz where the quartz will just shine with light and not really reflect mulitple yellows and pinks and so on.
Last Update: 23 Nov 2008