How to cut a stone on a White Dwarf? I've heard that white dwarf stars are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that? 
 A: A quick, inadequately researched answer, which I post because the question is already at -5, and so probably doomed... 
A white dwarf is a bit like a blob of white-hot burning liquid metal, spinning in space; the size of a planet but the mass of a star, so if you landed there you would be crushed to a smear of atoms less than a millimeter high, in an instant. Even if it had cooled down enough that the surface was solidified (and that might take billions of years to happen), you wouldn't be able to dig into it and extract a piece, because of the gravity. So there ought to be no stones, no mountains, no structures, even on an old cool black dwarf - everything will be crushed into flatness by the gravity. 
But when it's still hot, the star will have an atmosphere as well, and it seems remotely possible that small crystals might form there and somehow get away. Alternatively, if some catastrophic explosion somehow blew up the star or part of the star, perhaps some blobs of "white-dwarf crystal" would escape in one piece. Away from the crushing gravity, the electrons and nuclei would expand apart and rearrange themselves into a more conventional sort of mineral (made of carbon and oxygen, the dominant elements in a white dwarf). If such a fragment somehow made its way to Earth, it would just be an ordinary crystal and could be cut like any other mineral. 
Reader beware: I picked up most of this by speed-reading papers for the past hour, and also adding some physics common-sense. I may have missed something important. Also, human scientists undoubtedly do not yet understand everything about the environment in and around a white dwarf. So, believe what I wrote at your peril. 
A: We know that matter in White Dwarfs and Neutron stars become hugely dense, ten or fifteen orders of magnitude more dense than ordinary matter. What we don't know is, if such matter stays stable away from the deep gravity well of the star corpses where they form.
We certainly haven't found a single grain of such matter in nature after a couple of centuries of geological observations. But, such a dense material will not stay afloat in any kind of matter crust of any planet, quickly sinking toward the center of planets that capture such grains gravitationally.
If there is some kind of neutronium or strangelet matter with a stable low-pressure phase, the only three ways we are going to ever find out are:


*

*by recreating those densities and pressures in laboratory (our highest laboratory pressure diamond anvils top out at 40 GPa or something, 7 orders of magnitude less of what you are after, so good luck with that)

*We become extremely good at observing gravitational perturbations and optically check the sources.

*My favorite: We adventure a mining expedition to some old moon on the solar system that we are certain that is cool enough for us to go and drill toward the center of the core, and then we get to see what kind of heavy stuff is frozen in there.
A: The "surface" of a white dwarf is a mixture of hydrogen, helium and perhaps a trace of heavier elements. It is never (read this as many, many times the current age of the universe) going to cool down enough to solidify.
Solids exist inside the approximately isothermal interiors$^{1}$ of white dwarfs, at densities $\geq 10^{9}$ kg/m$^{3}$, once temperatures drop below a few million K. In typical white dwarfs this probably occurs within a billion years. The white dwarfs freeze from the centre outwards, because the melting point increases with density.
The typical pressure contributed by the degenerate electron gas in a white dwarf interior at these densities is $10^{23}$ Pa. So, if you want to preserve your bit of crystallised white dwarf that you have somehow mined from the interior, then you have to work out how to stop it exploding. And it is not just a matter of letting it cool down - the degeneracy pressure is independent of temperature. So this high density material simply is not stable unless you can work out a way of constraining it. The problem is similiar, though not quite as extreme, to that of constraining neutron star material.
So in summary, crystalline material at white dwarf densities will have such a high internal energy density (due to degenerate electrons), that it would be incredibly difficult to constrain or manipulate.
$^{1}$ Degenerate electrons have extremely long mean free paths and so the thermal conductivity in a white dwarf interior is very high.
