[boris]

I take it back. Amazing:

317 W/m-K gold
2200 W/m-K diamond

[Bernard Marx]

This is the easiest way to distinguish between CZ and diamond. Visually they are similar with approximately the same refractive index and dispersive properties. Both are isometric so are not double-refractive. CZ is about 5 times as dense as diamond but that's no help when the stone is mounted.

Interestingly, Moissanite passes the thermal conductivity test and might be misidentified as diamond. But it's strongly double-refractive and a trained gemologist can see doubling of the facet junctions when the stone is viewed in the right direction (the direction of single refraction is generally oriented perpindicular to the large table facet on the stone, so you have to know "how" to look for doubling).

[lafroste]

Wow. That IS amazing. I had no idea diamond conducted heat so well.