Comment by adrian_b

An interesting fact is that while almost all of the Solar System has started as gas, which has then condensed here into solid bodies that have then aggregated into planets, a small part of the original matter of the Solar System has consisted of solid dust particles that have come as such from the stellar explosions that have propelled them.

So we can identify in meteorites or on the surface of other bodies not affected by weather, like the Moon or asteroids, small mineral grains that are true stardust, i.e. interstellar grains that have remained unchanged since long before the formation of the Earth and of the Solar System.

We can identify such grains by their abnormal isotopic composition, in comparison with the matter of the Solar System. While many such interstellar grains should be just silicates, those are hard to extract from the rocks formed here, which are similar chemically.

Because of that, the interstellar grains that are best known are those which come from stellar systems that chemically are unlike the Solar System. In most stellar systems, there is more oxygen than carbon and those stellar systems are like ours, with planets having iron cores covered by mantles and crusts made of silicates, covered then by a layer of ice.

In the other kind of stellar systems, there is more carbon than oxygen and there the planets would be formed from minerals that are very rare on Earth, i.e. mainly from silicon carbide and various metallic carbides and also with great amounts of graphite and diamonds.

So most of the interstellar grains (i.e. true stardust) that have been identified and studied are grains of silicon carbide, graphite, diamond or titanium carbide, which are easy to extract from the silicates formed in the Solar System.