Organosilicon compounds

Despite silica being abundant in nature as the second most common element on earth, no substances of biological origin have been found that utilize silica in other forms than silica-oxygen compounds. This includes silicon-carbon bonds.

Why this did not happen is not fully clear, as it is possible to engineer enzymes, like reengineered cytochrome c heme proteins, to catalyze the formation of silicon - carbon bonds under biological conditions.

My guess is that is connected to the chemical properties of silicon:

• Silicon tends to form strong bonds with oxygen instead of carbon, resulting in highly stable, insoluble silica-rich rocks rather than diverse, water-soluble molecules.

• The Si–O bond is extremely stable and energetically costly to break, making it difficult for nature to produce Si–C compounds in water-rich, oxygen-rich environments like Earth's crust.

• Silicon atoms are larger and have electrons in more distant shells than carbon, making Si–C bonds weaker and less stable than C–C bonds. ​​

References:

1. Teaching nature the unnatural
2. Directed evolution of cytochrome c for carbon–silicon bond formation: Bringing silicon to life
3. Organosilicon Biotechnology

Silicon plays an important role for living entities at a lower stage of evolutionary development (silicate bacteria, simple algae, spore plants etc.) and also plants that are called "siliceous" by nature (due to their high silicon content). For higher animals and humans, silicon content is relatively small but plays a vital role. In the tissue of animals, silicon exist in three forms:

1. Water soluble inorganic silicon capable of passing through cell walls and be eliminated from the body.
2. Organosilicon compounds/complexes containing Si-O-C groups. These include ortho- and oligo- silicate ethers derived from cholesterols, proteins, carbohydrates etc. Compounds containing Si-C is not present in higher mammals but reported to be found in bacteria Proteus Mirabilis.
3. Insoluble silico- polymers. These include amorphous silica, quartz. The surface of these polymers is covered by a chemisorbed layer of organic compound containing hydroxy- and amino- groups.

More details can be found in Ref. 1

References

1. Biologically Active Compounds of Silicon by M.G.Voronkov and E.Lukevics, Russian Chemical Reviews, 38 (12), 1969
2. Allison A. C., Silicon compounds in biological systems, Proc. R. Soc. Lond., 1968, B.17119–30, DOI: 10.1098/rspb.1968.0053
3. Hrast, Martina & Obreza, A. (2010). The role of silicon compounds in living organisms. Farmacevtski Vestnik. 61. 37-41. (link)
4. Petkowski JJ, Bains W, Seager S. On the Potential of Silicon as a Building Block for Life. Life (Basel). 2020 Jun 10;10(6):84. doi: 10.3390/life10060084.

In order for C-Si bonds to not exist as part of an extended Silicon Carbide Ceramic structure, there are precious few options to terminate the Silicon into a molecular form. Hydrogen would be a reasonable starting consideration given abundance, but so would the halogen elements and various cyclic structures. However, even under assumption of their formation, water and oxygen (in molecular or other oxidizing speciation) would immediately hydrolyze such structures to silica. This is a well known reason why any such molecule presents handingling challenges in the laboratory. (See properties of methyltrichlorsilane) As another consideration, stump your friends with this question: " Where is silicon carbide mined"? Trick question. It is not. Silicon carbide is not known to exist as a mineral. This is because despite its thermal stability it is oxidized to silica itself on sub-ge9ligical timescale. Hence, virtually all Silicon on the planet is bonded to oxygen. The most abundant elements in earth's crust: 1) Oxygen 2) aluminum 3) Silicon. (See USGS) Silicon dioxide is common, but despite their nearly endless variety most rocks are a species of aluminosilicate.