Lithoids are rock-bodied people, a concept borrowed from Stellaris and the silics of Endless Space and Endless Legend. Like the Minervans, the Uymon'ea and the M'Lak, they come from the sector the 12th Fleet escaped at the start of the story, where their homeworld was destroyed and they had lived as asteroid miners. They are mostly humanoid in shape, and not every one is the same mineral: the fleet's own, Thumno, is bismuth-based, metallic and shimmering where most are plainly rock-like.

Body

A Lithoid is solid in every sense. They subsist on minerals, can survive direct exposure on frozen, burning or airless worlds, and stand up to radiation better than humans. Thumno needed no cold-weather gear on an ice moon, wore nothing more than an atmofilter and a backpack, and offered to go through the radiation-marked doors because his crystal was more resilient than the humans with him. Burrowing creatures that went straight through human flesh found his hard exterior heavy going. In a pinch bits of a Lithoid make passable spare parts, and the party on that moon made pitons out of spare parts flavoured as pieces of Thumno.

The price is speed. Lithoids are glacially slow, always last to act and slower on their feet than a human, though what they do they do with care.

Mind

They come across as patient, literal and kind. Thumno speaks of himself as "this crystal", calls everyone "human" followed by their name, does not shoot ("Thumno only fix or break with wrench") and offers comfort with a heavy shimmering hand on the shoulder. His tastes run to ore and, by way of dessert, bubblegum-flavoured ice cream that is actually Pepto-Bismol.

In the fleet

Thumno Unkrux is a civilian engineer in Hercules engineering, carrying a large quantum wrench, who went with the A Blip in the Dark party to the ice moon.