Lithophiles are

micro-organism A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

s that can live within the pore interstices of

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

and even

fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

rocks to depths of several kilometers. Some are known to live on surface rocks, and make use of

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

for energy. Those that live in deeper rocks cannot use

to gather energy, but instead extract energy from minerals around them. They live in cracks in the rock where water seeps down. The water contains dissolved

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(CO₂) which the organisms use for their carbon needs. They have been detected in rocks down to depths of nearly three km, where the temperature is approximately 75 °C. Terrestrial lithophiles can be found in canyons primarily composed of

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

, an igneous rock, and soils saturated with fractured rock. Organisms from the genus ''Elliptochloris'', a subaerial photosynthetic green algae, demonstrate lithophilic preferences through colonization in granite cracks and in proximity to terrestrial

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

s. Lithophilic lichens from the genus '' Collema'' form tight symbiotic relationships between fungi and photosynthetic algae such as ''Elliptochloris'' in order to produce necessary saturated fatty acid secondary metabolites. Lithophilic algal species colonizing fractured rock outcroppings individually exhibit coccal morphological shape while aggregating into an elliptical or globular arrangement during adulthood. Lithobiontic ecological niches further classify lithophiles into sub-categories determined by their spatial niche specificity. The term, lithic, refers to an association with rock and can be further explained by the term, lithobiontic, regarded as organisms living both on, and within rock surfaces. Sub-surface rock organisms, endoliths, primarily exhibit niche preference within fissures, cavities, or tunnels of various rocks. While many endoliths degrade and effectively excavate the available

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

rock surface, many are preyed upon by select

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

, and

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

species. This habitat preference can be further threatened by suspension feeding organisms searching for acquired shelter.

References

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