The pre-solar grains are microscopic crystals, i.e. particles of dust, which have come to the Solar System as already solid grains of dust, from other stellar systems, typically having been propelled by stellar explosions, e.g. those of supernovae.

Such pre-solar grains have been incorporated in the many small bodies that have been condensed from gases along with the bigger asteroids and planets at the formation of the Solar System.

Some of those small bodies have fallen on Earth as meteorites (the so-called "chondrites"). When such meteorites have been analyzed carefully, pre-solar grains have been recovered. They can usually be easily distinguished from the local objects, by having very different isotopic compositions.

Among the pre-solar grains, there are many that have come from stellar systems of the second kind, with more carbon than oxygen. Such grains, instead of being silicates, i.e. the most frequent minerals in the stellar systems of the Solar type, have chemical compositions that are unusual for the minerals of the planets of the Solar System, like diamond, graphite, silicon carbide or nitride, titanium carbide or nitride, metal grains of either platinum-group metals or iron-group metals, other carbides, nitrides, sulfides, silicides or titanides.

For now, this is the only direct evidence of the second class of stellar systems, beyond the spectroscopic observations of various stars, which provide estimations for the relative abundance of carbon and oxygen in those stellar systems.

While we have some idea about what kind of minerals might be the most abundant in such stellar systems at the time of their initial condensation from gases, I am not aware of any attempt to simulate the possible internal structure for big planets in such stellar systems, in order to determine whether in such planets there could exist some analogs of the volcanism and hydrothermal vents that can provide the energy flux necessary for the appearance of life in the planets of the terrestrial type.

For instance, many living beings, from bacteria to vertebrates make and use magnetite crystals, for sensing the magnetic field of the Earth.

Magnetite contains iron ions and pure iron is a metal. Nevertheless, magnetite is not a metal, but a ionic crystal, i.e. an insulator. Your blood contains iron and your bones contain calcium, but none of that iron or calcium is in metal form, all are oxidized ions.

There are no living beings that have metallic components. There are a few bacteria that are able to reduce to metallic form the metals that are the easiest to reduce, i.e. gold and silver. However those bacteria do not use in any way the metallic gold or silver that is precipitated outside their bodies by their activity. The reducing of gold and silver is just a defense mechanism for those bacteria, because the ions of gold or silver kill bacteria, and their precipitation when they are reduced removes them from the environment.

As I have said almost all metallic elements present close to the surface of the Earth or of any other planet of this type are oxidized, i.e. they are positive ions that are bound in various ionic substances, like oxides or sulfides, and they can be found inside the bodies of the living beings in the same state as outside (unlike carbon, nitrogen and sulfur, which are oxidized outside, but reduced inside the bodies of the living beings).

Only a few metallic elements are found also as native metals, i.e. copper, silver, gold, mercury and the platinum-group metals. Even for these metallic elements, most of them are far more abundant in oxidized forms (like sulfides or arsenides) than in metallic forms. Only gold is more abundant in metallic form than in oxidized forms, like tellurides (and that is due in good part to the fact that tellurium is also a very rare element, otherwise more gold would be found combined than in metallic form; the gold ions are extremely large, so that they cannot combine well with ions smaller than the telluride ion, like the sulfide ion that combines well with the smaller silver ions).