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How would an alien organism survive on a diet of rocks and mineral ores, and what kind of materials would be the most sufficient? Also, what kind of teeth and evolutionary traits would they possess in order to support this geophagic diet? I've researched animals such as the chiton, limpet and sea urchins, who also have strong teeth made of magnetite, goethite and calcite respectively, sea urchins possessing self sharpening teeth as well. I'm currently playing with the idea of this organism being an evolved humanoid chiton similar to how an Inkling from Splatoon is an evolved squid humanoid. The only other fictional race I am aware of that has a geophagic diet are Gorons from Zelda, but I am not sure why they eat rocks other than the fact its fantasy.

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Lithotrops. That's the name.

The comment by @starfish prime is correct: the consumption of reduced inorganic compounds (RIC) is essential: Energy is derived via oxidation. That is why hydrothermal vents are the main source of RIC. There are no large organisms on Earth feeding on RIC.

Known chemolithotrophs are exclusively microorganisms; no known macrofauna possesses the ability to use inorganic compounds as energy sources. Macrofauna and lithotrophs can form symbiotic relationships, in which case the lithotrophs are called "prokaryotic symbionts"

It is possible, however, that larger organisms develop a symbiotic relationship with those microorganisms. One good solution to your large human-like creatures living on land is to live close to volcanoes. They live on a geologically-active planet with abundant sulfur vents. They eat sulfur deposits and derive energy by oxidizing sulfur to sulfates. The energy drives growth and metabolism that uses additional minerals as building blocks. Also, by saying "inorganic" you exclude carbon almost completely. It is possible to absorb carbon dioxide for biosynthesis rather that handwaving a silicon-based life

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    $\begingroup$ One problem with lithotrops as a dominant macroscopic life form is that they are limited by their food supply. There's really not that much of (or perhaps that fast of) a "lithocycle" that corresponds to the protosynthesis-driven carbon cycle that powers most life. $\endgroup$ – jamesqf Nov 30 '19 at 19:16
  • $\begingroup$ Yes, I mentioned that in the quote. The sulfur-based chemosynthesis may offer some partial solution. Other freshly-exposed minerals can be oxidised for energy as well. I still think that if such large organism evolves, it may be sluggish and cold-blooded for the same reason you stated. $\endgroup$ – Christmas Snow Nov 30 '19 at 19:45
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These animals can eat whatever releases energy upon reaction with another chemicals.

For example if they live on a planet with an oxygen rich atmosphere, they can eat carbon, iron or any other oxidable metal.

Their metabolism will use the oxidation path, which for carbon would be $C+O_2=CO_2 + Energy$ to get energy and sustain themselves.

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    $\begingroup$ You will of course have problems finding oxidisable metals in their native unoxidised state for very long, once the planet has developed an oxygen atmosphere (see also: history of Earth). We do however have excellent reserves of carbon-rich minerals derived from dead trees. $\endgroup$ – Starfish Prime Nov 30 '19 at 15:34

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