Topaz is an uncommon ore that you can get from Rare Stone Tali and Rare Ore Deposits.

Sources of Topaz

Topaz has a fair chance of coming from Rare Ore Deposits, and a rare chance of coming from normal Ore Deposits.

You also have a fair chance of getting topazes when you defeat Rare Stone Tali, and a low chance of getting topazes from Luminous Stone Tali.