Molten salt seas on the future Earth As the sun gets brighter, the oceans are expected to evaporate by the next billion years or so (the vapor slowly gets stripped off into space). The salt, which is less dense than most rocks, will be left behind. Then wait another couple of billion years. Most rocks melt at a higher temperature than sea salt: basalt melts at around 1000C, quartz melts at 1713C, but NaCl melts at only 801C (adding other salts will lower this). So will a tangerine sun loom large over red-hot waves softly breaking on abyssal beaches?
So will a tangerine sun loom large over red-hot waves softly breaking on abyssal beaches?


Probably not. Interesting question, and one might think that yes - you could melt the evaporite deposits that will be left after all the water is gone.

The problem is that molten salts are extremely reactive materials. They will corrode any rock they get into contact with. As most rocks on the ocean floor are silicates (basalts etc) you will just get chloride-silicate minerals. For example, the reaction between halite and nepheline (a fairly common silicate mineral) will lead to the formation of sodalite (another fairly common mineral):

$\ce{6NaAlSiO4 + 2NaCl = Na8(SiAl)6O24Cl2}$

There's a long list of known chloride-silicate minerals, and for a more realistic salt–basalt reaction the products can be things like scapolite, adrianite, or wadalite.

You will most likely end up with no salt, overlying a somewhat thin (metres?) layer of these silicate-chlorides. It could be that in some points you might have ephemeral pools of liquid salt, or in places where the chloride-silicate layer is thick enough to effectively isolate the liquid salt from the silicate rocks below, but those will probably be negligible features on the scale of the planet.

One final comment:


  quartz melts at 1713C


In isolation. When quartz is mixed with other things (like feldspars in a granite), it melts at a lower, eutectic, temperature.  See related question one and two.