4 ms·

I know nothing, but my physics instincts say any vapor that might form crystals would evaporated in the eternal vacuum.

• nitrogen 5y ago
  Vacuum deposition is a thing.
  • Tagbert 5y ago
    Yes, but the result is usually a more granular, friable substance rather than a cohesive crystal.
    • ncmncm 5y ago
      Have you heard of "molecular beam epitaxy"? You can make functional microelectronics with vacuum vapor deposition.
• ncmncm 5y ago
  This is the same argument as saying since all the stuff that might be deposited on (say) a gypsum crystal can dissolve in water, the water would carry it all away and there would be no gypsum crystals. But we do, in fact, get gypsum crystals: http://i0.wp.com/unusualplaces.org/wp-content/uploads/2016/07/1200px-Cristales_cueva_de_Naica.jpg http://i0.wp.com/unusualplaces.org/wp-content/uploads/2016/0... A likely process would be a (maybe impure) deposit of a mineral at one end of a tunnel, with a heat source, whether the sun through a skylight or thinner roof, or a geologic hot spot, causing the mineral to sublimate, howsoever slowly, and some of the vapor migrating to a colder part of the tunnel, and crystalizing out there.