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Heat tolerance of semiprecious and precious stones


When heat hardening argentium silver, it is in a kiln at 573 F for 1-3 hours. How will this temperature effect already set stones such as zircon, spinel, tourmeline, sphene, etc. as well as other more common precious and seemi precious stones.


Hi Acquaria,

This temperature could definitely have an effect on certain gems. Aquamarine and some varieties of quartz undergo heat treatment at these temperatures, and their color may be altered. There’s more information in our beginner’s guide to gemstone treatments.

Many stones are also sensitive to heat. Our gem value, price, and jewelry information pages give a qualitative “heat sensitivity” for each gem. For example, in tourmaline it says “some” and in spinel it says “no.” Similarly, zircon is not sensitive to heat but sphene is.

Opal and emerald are two that come to mind as being extremely heat sensitive, and may be damaged in this process.

Geologist and IGS Team Member


Thank you Addison, that basically answers my question. I will further research the guide to gemstone treatments.