Fossil is an organic mineral used primarily as a source of Lime for Steel production. It appears naturally in Oasisse, especially in the Oil Biome, and in smaller amounts in the Tide Pool Biome. It can also be generated by the Ancient Specimen story trait, where completed Fossil Fragments near points of interest can be excavated for large quantities of Fossil, and the trait converts Diamond into Fossil at a 1:100 ratio.
Its main industrial use is in the Rock Crusher. Unlike most materials processed there, Fossil does not turn into Sand; instead, 100 kg Fossil produces 5 kg Lime and 95 kg Sedimentary Rock. This makes it a direct alternative to Egg Shells when supplying Lime for Steel, while also leaving behind a useful sedimentary byproduct. Fossil can also be used as a general building material.
In Oasisse, Fossil is part of the map’s broader late-game resource layout, alongside scattered Oil Biome patches and other sparse deposits. Since the asteroid has no natural Wolframite and lacks several common biome types, Fossil is one of the more relevant native resources for industrial expansion there. The material also has interesting thermal behavior when produced by the Ancient Specimen trait: Fossil inherits the temperature of the Diamond it is converted from, which can make the resulting stockpile substantially hotter or colder than surrounding materials.
