'''Sol stones''' are [[valuables]] with negative weight of -1000 gvolume and mass, making your load lighter just by being in your inventory. A natural onyx sol stone has a mass of negative 1000g, but it is possible to use a [[scroll of change material]] to change it into a negative volume of some very dense material, creating a larger negative mass and reducing inventory weight even further. Keeping a few sol stones in a container "unfills" it, making space for other items. Wielding an item with negative mass has very strange effects. Originally being impemented in the [[CLIVAN]] variant, they were ported back into vanilla in [[Version History|0.50.9 release]].