It is true, though, that diamond and moissanite pass the diamond
testers, while other gems should not. But that's only one measure,
One measure of what?
Your statement implies that all other gems conduct no heat, and
that's just not true.
I do not believe what I wrote implied any such thing. In the context
of using a thermal tester, only moissanite and diamond respond
positive. What is implied is that all other gems do not test positive
with a thermal tester. That is true.
The original post was about a “synthetic zircon” being tested with a
diamond tester and getting a positive for diamond. Someone replied
The diamond tester works on the principle of heat conduction and
diamond conducts heat better than most other gems with synthetic
moissanite (silicon carbide DR) being close and sapphire/ruby (DR)
being a distant second.
I believe in the context of a discussion about someone getting a
positive indication on a “synthetic zircon” using a diamond tester,
I feel I was clear that diamond and moissanite are the only gems that
test positive as diamond with a thermal tester… That is true. No
gray there. That all gems can conduct some heat is meaningless in the
context of using a diamond tester. Other than separating diamond and
moissanite from all other gems, a diamond tester is useless for
identifying any other gem. No gray there.
I felt I was clear that if only diamond or moissanite test positive,
ruby and sapphire cannot be a distant second. They are not on the
list of gems that can be identified by thermal conductivity. No gray
The discussion was not about how to identify diamond from moissanite
or either from ruby, or sapphire.
Prior to moissanite, only diamond would test positive with a thermal
tester, the only reason for the thermal tester, in my opinion, was
when C.Z.'s came along. Gemological testing advances in relationship
to the synthetics and stimulants that are developed that can be
mistaken for diamond. Diamond is the only natural gemstone that I
know of that will test positive with a thermal tester.
Richard Hart G.G.