Charts and Reference

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Firing Gemstones and Natural Stones in Art Clay®

Provided by Art Clay® World

This chart provides information on the gemstones and natural stones that can be safely fired with Art Clay and which stones should be avoided. Use the following key to determine what stones are safe to use with the Art Clay products available:

** - can be safely fired in place with Art Clay Silver Standard and Slow Dry Formula, in addition to all 650 Series.
(650) - can only be fired with Art Clay Silver 650 Low Fire Series.

Elected Gemstone Characteristics
Stone Hardness (Mohs) Specific Gravity Refractive Index Dispersion Durability
Alabaster 2-2.4 2.2-2.4 1.52 med-high low
Alexandrite** 8 3.68-3.79 1.54-1.75 low high
Amber 2.5 1.03-1.10 1.54 none low
Apatite (650) 5 3.16-3.22 1.64-1.65 low medium
Aquamarine 7.75 2.68-2.70 1.57-1.58 low high
Azurite 3.5 3.8 1.48-1.65 none low
Beryl (650) 7.75 2.68-2.70 1.57-1.58 low high
Cat's Eye** 8 3.68-3.79 1.54-1.75 low high
Chalcedony 7 2.65 1.55 low high
Chrysoberyl** 8 3.68-3.79 1.54-1.75 low high
Corundum** 9 3.95-4.10 1.762-1.770 low high
Diamond 10 3.52 2.42 high high
Emerald** 7.75 2.66-2.70 1.57-1.58 low high
Epidote 6 3.25-3.49 1.73-1.76 med-high high
Feldspar 6-6.5 2.54-2.58 1.522-1.530 low medium
Garnet (650) 7.5 3.70-4.16 1.74-1.89 med-high high
Gypsum 1-1.5 2.3 1.53 med-high low
Hematite (650) 5.5-6.5 4.95-5.30 2.94-3.22 none high
Jade / Jadeite 6.5-7 3.30-3.38 1.66-1.68 none high
Jet 3.5 1.1-1.4 1.64-1.68 none low
Kunzite 6.5-7 3.18 1.660-1.676 medium low
Labradorite (650) 6 2.70-2.72 1.55-1.57 medium medium
Lapis Lazuli 5 2.76-2.94 1.5 none medium
Malachite 3.5-4 3.25-4.10 1.655-1.909 none low
Marble 3 2.71 1.48-1.65 none low
Moonstone (650) 6 2.58 1.518-1.526 low high
Nephrite 6.5 2.96 1.62 none high
Obsidian (650) 6 2.33-2.60 1.48-1.51 high medium
Olivine 6.5-7 3.3-3.5 1.654-1.690 medium high
Opal 6 1.97-2.20 1.45 none low
Peridot (650) 6.5-7 3.3-3.5 1.654-1.690 low medium
Quartz 7 2.65 1.55 low high
Rhodonite 5 3.53 1.73-1.74 none medium
Ruby** 9 3.95-4.10 1.762-1.770 low high
Sapphire** 9 3.95-4.10 1.762-1.770 low high
Serpentine 3.5 2.5-2.7 1.57 low low
Sodalite 5 2.13-2.29 1.483 low medium
Spectrolite (650) 6 2.70-2.72 1.55-1.57 low medium
Sphene 5-5.5 3.52 1.95-2.05 high medium
Spinel** 8 3.6 1.72 low high
Spodumene 6.5-7 3.18 1.660-1.676 low low
Steatite (soapstone) 1-1.5 2.7-2.8 1.540-1.590 none low
Topaz (heat diff.)** 8 3.54 1.63 low medium
Tourmaline 7 3.06 1.63 low high
Turquoise 5 2.6-2.8 1.61-1.65 none medium
Zircon 7 4.02 1.81 high high

Warning: Do not subject stones with fractures or heavy inclusions to direct heat (such as a torch or kiln). This could cause the stone to explode. Fire Mountain Gems cannot be responsible for stone breakage or accidents resulting from firing gemstones.

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