How much larger would a star have to be to cause thermonuclear reactions if it was made out of mostly rock like Earth, instead of gases?

I assume it would have to be considerably larger since rock isn't as flammable as gases are? But it's also more dense to begin with..

Do we know of any suns that are made like this?

Is it even possible to have a thermonuclear reaction with solid rock?

• A body that large would rather collapse into a neutron star (or black hole) instead of undergoing fusion. Jul 1 '15 at 20:41
• @FlorinAndrei that's not strictly true. Rock, mostly Silicon and Oxygen would undergo some kind of type 1 supernova explosion as Rob Jeffries describes and in the process, blowing off a fair amount of it's matter. Fusion needs to reach the Iron stage before a Neutron Star of Black Hole could form. Nov 29 '15 at 15:27

"Rocks" are made of atoms of silicon and oxygen (for example) in the form if silicates. But these are dissociated at fairly low temperatures compared to the centres of stars. Oxygen and Silicon thermonuclear fusion ignition requires temperatures in excess of $10^9$ K, and these temperatures are only reached late in the lives of stars of mass $>8 M_{\odot}$.
Ordinarily, the cores of white dwarfs are inert as far as nuclear reactions are concerned, because the temperatures are too cool. However, if the white dwarf is massive enough (or mass is added to it), then the central densities climb, and for white dwarfs of mass $\sim 1.38M_{\odot}$ it is thought that the densities become high enough ($\sim 10^{13}$ kg/m$^3$) to start nuclear fusion of carbon via the zero point energy oscillations in the crystalline material (so-called pyconuclear reactions). Such reactions in degenerate matter are highly explosive and might result in the detonation of the whole star in a type Ia supernova.