What's the safest rock to have submerged in boiling water?

big diamonds, cheap and affordable

If youre serious, youd need to make sure thw rocks you choose do not have any sulfurin them (and thats damned difficult because defect Xl lattices usually contain elements of the Sulfur family of elements).
Hyperthermophylic archaea can live in boiling water as long s they can hqve some sulfur to munch on.
A rock Id choose wouldnt be a rock, itd be a peice of 1,1silane in a ring with (cyclo) siloxane (hydrated forms of quartz gel mixture made in a lab and can be made to "set up" like a paperweight.
OR have a pice of crystal glass drop forged with a hole so that you can attacch the implement to be sterilized. I think the silane cyclosiloxane has a p grav about that of quartz so Itll sink

I dont know why you wish to do this when pressure & T works fine.


what are you sterilizing anyway?

lol

Thank you for the thoughtful reply! I feel bad that you went to that much trouble, I'm just making an artsy little doodad to sterilize kitchen sponges to get the smell out. The rock would hold the sponges (tied to the rock with wire) under the boiling water. I was worried that some rocks might explode or release something toxic. I feel like I wandered on to the wrong site with my question. My apologies if that is the case.

Farmer is a long time geologist and has a sense of humor. Of course he can answer for himself. I type better (he has a disabled hand). If you are interested in rocks at all, he's the guy to talk with, as a beginner or more advanced.
I get you just asked a simple question.