What gemstones are the most heat-resistant?

[Braininthejar2]

I was going to make a "high priest's ceremonial robe, studded with gems to create a flame pattern" as an I type treasure in my adventure.

But then I realised he's a fire giant high priest, who sacrifices people by dunking them into lava - so if I covered him in ambers, they'd likely melt and catch fire.

What should I use?

[Yora]

Zircon can be heated up to at least 1,000°C. Which should be enough to survive the heat of most lava, though it turns the crystal blue.

The bigger question would be how the fire giant is going to wear it without its robes getting incinerated first.

[hamishspence]

Asbestos robes? Chrysotile can stand temperatures of up to 550 C before it starts to dehydrate.

Still would need pretty cool lava - like this kind:

https://en.wikipedia.org/wiki/Ol_Doinyo_Lengai

[Braininthejar2]

Skin something with a fire subtype?

[snowblizz]

If I understands the table correctly, you want diamonds. Which would not be surprising since diamonds form from coal under enourmous pressure and heat deep in the earth's mantle or something.

https://www.gemsociety.org/article/t...operties-gems/

Apparently you can (and do) heattreat some gemstones at plus 1000C for a while to improve them.

[Aeson]

As far as gemstones go, corundum (sapphire, ruby; note that non-blue sapphires are available, though the color of the gem can change permanently when the gem is heated) could work.

As far as robe materials go, you could perhaps use a metal thread or foil to make the robe. Depending on just how hot the fire giant and the sacrificial chamber are, you might be able to get away with gold (melts at 1337K) or silver (melts at 1235K); Wikipedia indicates that magma is usually between 973K and 1473K.

Also, since you seem to be somewhat concerned about real physics, be aware that lava is generally ~2-3 times more dense than humans are and that it's a very viscous fluid, meaning that it's a bit difficult to submerge a person in lava if you're throwing them into the pool in the traditional way. Depending on what exactly you're envisioning when you say 'sacrifices people by dunking them in lava,' you might need something a bit more complex than just a pool of lava into which the high priest can throw the sacrifices.

If I understands the table correctly, you want diamonds. Which would not be surprising since diamonds form from coal under enourmous pressure and heat deep in the earth's mantle or something.

Be warned that diamond starts turning into graphite in air at around 973K and will start to burn somewhere around 1123-1273K. Also, the linked table does not include the melting and ignition points, which are pertinent to a discussion of which gems are reasonable for use on the robes of a fire giant who spends time in and around lava. Most of the information given in the table relates to how much energy is required to change the temperature of the material, how quickly the temperature of the material changes, and how quickly heat spreads through the material, which is useful if you're willing to do some math and can bring in additional information (temperature of the giant and the lava in the sacrificial chamber, melting and ignition points of the gems, how long the giant is going to be wearing the robe, how long the giant is in the chamber, what temperature the gems start at, etc) but is not particularly useful otherwise.

[Braininthejar2]

I don't need him to actually submerge himself, just stand close enough to the pool that a human would go Anakin if he did. I'm thinking gold and fire agates...

The lava being too dense for humans to submerge just makes them suffer longer, but he worships Imix, so it's ok.

[JNAProductions]

Remember-game. Fantasy game. Use whatever gems you like-if your players object based on science, point out that this giant could easily have enchanted the gems to be heat-resistant.

[Braininthejar2]

Now a more rules related question.

How large would a 5000gp fire agate be? Agates are cheap enough that I could make them quite big, and there is a huge statue of Imix in the temple, so I wanted to add some in its eyes as treasure.

[hamishspence]

Maybe have a geode - cut so that each side is roughly symmetrical and lined with crystals - and installed in the statue's eye sockets.