Lithophile

Lithophiles are micro-organisms that can live within the pore spaces of sedimentary and even igneous (if they are cracked—no natural space in igneous) rocks to depths of several kilometers.

Some are known to live in surface rocks, and make use of photosynthesis for energy.

Those that live in deeper rocks cannot use photosynthesis to gather energy, but instead extract energy for minerals around them. They live in cracks in the rock where water seeps down. The water contains dissolved carbon dioxide (CO2) which the organisms use for their carbon needs. They have been detected in rocks down to nearly 3km, where the temperature is around 75°C.