HarJel is a valuable substance discovered on Strato Domingo by a Clan Sea Fox "fishing expedition" when they scoured the Clan Homeworlds for valuable resources. The naturally occurring substance is a jelly-like liquid that can quickly be hardened to withstand the stress of vacuum. The black gel is now widely used as a hull sealant and for similar purposes (see below).
The monopoly was threatened after the Great Refusal, when Clan Hell's Horses and Clan Ice Hellion developed a way to create a synthetic replacement for HarJel. When Clan Diamond Shark found out, they moved quickly to stall the research project and seize the Ice Hellion facilities while the warrior caste was still unawares of their scientist caste's breakthrough.
In April of 3065, the Diamond Sharks took over the Twycross system from Clan Jade Falcon and discovered an organic compound almost identical to HarJel on Jonah's Reach, an uninhabitable outer planet in the system.
In August of 3065, Clan Diamond Shark acquired the world of Itabaiana from Clan Nova Cat to serve as one of their base worlds in the Inner Sphere. Among other concessions, the price included two percent of the HarJel production from the Twycross system.
HarJel is used in several capacities:
- As a component of Elemental armor it is used to absorb shock, seal breaches in the armor and control bleeding should the Elemental warrior be wounded
- As hull sealant on Clan spaceships
- The BattleMech HarJel System, later refined to HarJel II and HarJel III
- Field Manual: Warden Clans, p. 59, "Fishing Expedition"
- Field Manual: Warden Clans, p. 59, "The Golden Century"
- Blood in the Water
- Masters and Minions: The StarCorps Dossiers, p. 152, "Trellshire Heavy Industries", and p. 153, "Key Worlds of the Diamond Shark Clan - Twycross"
- Masters and Minions: The StarCorps Dossiers, p. 147, "New Waters", and p. 154, "Key Worlds of the Diamond Shark Clan - Itabaiana"