Solacite ("solace stone") or relief gem, is padparadscha (or any similar-looking pink stone) believed to be infused with relief (as in, the opposite of pain), and which can absorb and transfer this relief energy to and from sentient minds - meaning, primarily, humans. It is a type of enchanted gemstone in that peoples' beliefs that they hold relief gives it that property. The larger the solacite, the faster it can absorb or dispense relief, and the more relief it can hold.
It is believed to be charged by stabbing someone, and once stabbed, the gem 'collects' relief by 'extracting' it - in other words, at the cost of inflicting its victim with agonizing pain, hence the solacite is also known as a pain stone or a pain gem. Since people would not normally be willing to submit to such pain, users of solacite generally must first find humans to enslave as "pain slaves". As the sole use of pain slaves is to keep them in as much pain as possible, as often as possible, and that is exactly what piercing by solacite does, this is among the worst possible fates that can befall a slave.
Solacite, when not in contact with blood, provides pain relief (the titular solace) - though only from pain, not relief from mental anguish, nor can it provide satisfaction or elation. It is commonly awarded or sold to soldiers, guards, or heroes who have done a deed the owner of the solacite found fit to reward. Wearing solacite into battle allows a soldier to fight on, at least for a while, without feeling any sense of pain from their injuries - until the relief becomes expended. This means a faster ability to recover from painful injuries, and ability to respond to attackers, which in turn increases their survival rate.