Board Thread:Theories and Speculation/@comment-33486170-20171124080415/@comment-734582-20171126110252

Namikazenaruto9 wrote: Well if you are so keen on saying that what about rocks being conductor of heat? Silicon(which should be most of it) is good conductor of heat. The conduction of heat for a material is heavily dependent on how well it carries thermal phonons (note the n), thermal electrons and (for porous materials) internal radiation. Phonons are essentially elastic waves: atoms vibrating in a coordinated effort.

Metals conduct heat very well because electrons can freely move through the material and so easily distribute heat, while the rather uniform crystal offers minimal thermal phonon resistance. Alloys, inclusions and fine-grained metals are worse at conducting heat than pure metals. Conductivities are in the order of 10-100+.

Stones on the other hand are ionic materials which have different sizes of ions so they naturally conduct heat worse. The electronic contribution is also low. Conductivies are in the order of 1-10.

Air is a horrible conductor of heat because it's mode of transport sucks. Hot molecules have to move to the cold side, meaning that the randomly moving and bumping atoms have to cross large areas. In a solid material, the coordinated movement is only in fractions of nanometers. You could imagine it like a newton's cradle: the transmission of the movement through the still balls appears instant compared to if the ball had to physically move and touch the outer ball. The conductivity of air is in the order of 0.01.

It means that if you had an infinitely large plate of 1m thickness, one end is 0C and the other is 1C, then a stone plate would conduct 1-10 watts of heat while a metal could conduct tens to hundreds of watts. Alternatively, a plate subjected to a certain amount of watts would have a more uniform temperature when it is a metal than that it is a form of stone.

However, you're not talking about uniformly heating up a stone but rather melting it. Melting it would cause the hot stone to move out of the way and expose more fresh stone. So a low conductivity is actually beneficial (assuming for a moment that you don't want to uniformly melt a stone).

Also note that the actual chemical composition is of little importance unless you compare similar materials. A gas will pretty much always conduct worse than a liquid, which conducts worse than a solid, and a uniform crystalline material (ie a pure metal) will always conduct better than an amorphous material (e.g. glass).