In addition to the "bones don't melt" answers which can be supplemented with "meat does not melt", it is interesting to note what happens on the rare occasions that people have fallen into lava. read more
Lava doesn't melt people because people don't melt, anyway. Too much heat and first we die, then the water boils away, and then whatever solids are left over can melt. read more
February 11, 2018 2.09pm EST Although it is very hot, when lava flows over the ground, it generally does not melt the soil or rock. read more
Assuming you mean melt from any natural temperature of Earth lava, there is metal that the evidence indicates can’t melt from any natural temperature of Earth lava. Tungsten, iron, nickel, cobalt, beryllium, platinum, and titanium all seem to have melting points above the hottest Earth lava. read more