A preservation amulet works by monitoring the wearer's vital signs, and petrifying them if they suffer a sufficiently serious injury. The petrification process is actually a phase transmutation rather than a substance transmutation, so they are not literally turned to stone, but rather a room-temperature solid. However, since biological processes cannot occur without liquid water, the wearer's metabolism ceases in this state. Moreover, the relative hardness of the petrified state tends to protect the wearer against further injury, as normal weapon damage has little additional effect against them. Since their blood is turned to a solid, they cannot lose additional blood once petrified.
The purpose of a preservation amulet is to prevent the wearer from dying between the time they take a potentially fatal injury and the time they receive medical attention. Thus, a person who is wearing a preservation amulet will not bleed to death on the battlefield; in fact, almost all stages of death cannot occur in the petrified state. The amulet can be deactivated after the battle when healer mages are ready to act. This causes the wearer to revert immediately to flesh. Ideally, the healers present will be able to correct the injury the wearer has suffered before it actually results in death.
Mortality rates among soldiers with preservation amulets tend to be very low, typically only a few percent of casualties. The only way to kill a person who is wearing a preservation amulet is through massive and irreversible trauma to the central nervous system, for instance cutting the head off or putting a large hole in the skull. Even in these cases, a very skilled healer will sometimes be able to restore them to life, albeit with permanent brain damage that renders them useless as soldiers.
The main weakness of the preservation amulet is that it does not protect a soldier against capture. If the wearer is captured, their captor may or may not care about their life, so the preservation amulet might be deactivated without any healers present. For this reason, units that are primarily equipped with preservation amulets place a very high priority on capturing the battlefield. The Gomla in particular were noted for their utter fanaticism in battle. Such units are sometimes referred to as "immortal" because of their tendency to ignore casualties.