|This article is a stub. You can improve Gold Refining Wiki by expanding it.|
Cubic zirconia (colloquially CZ) is a tough, often synthetic gemstone that serves as a diamond simulant.
It can be distinguished from diamond by its thermal conductivity, much lower hardness, higher toughness, lack of electrical conductivity, and of course, by its reactivity towards hydrofluoric and/or hot, concentrated sulfuric acid. The acid treatment (typically with HF acid) of bulk diamond melee obtained from gold refining of karat jewelry scrap is conducted to "frost" cubic zirconia so that they may be visually sorted out from the unfazed/unetched diamonds.