What is the effect of pressure in solids?

Answer 1

For most solids, increasing the pressure will also increase the melting temperature. A notable exception is ice.

Although solids are not very compressible, extreme pressure will still compress solids to a measurable degree.

Some solids will also undergo phase changes when subjected to increasing pressure - from one solid structure to another. As previously noted, ice may actually melt if pressure is applied near the melting point temperature of the ice (a solid to liquid phase change vice a solid/solid phase change). A good example that most people are familiar with is the formation of diamonds. The tetrahedral crystaline structure of diamonds is actually not thermodynamically stable at atmospheric conditions, but from a kinetic standpoint the conversion back to graphite or other stable solid structure is so slow that it might as well be stable. To get it to convert to the diamond structure requires very high pressure.

Answer 2

At higher pressure, solids melting temperatures will be lowered, therefore at very high temperatures a rock could melt at 20 degrees for example. this is used in industry to reduce the cost of melting stuff, such as in the haber process. the trick is to find the balance between increasing the pressure and raising the temperature, as higher pressures are more dangerous so cost more.