First of all, it was recently discovered that despite the temperature and matter density being cosmically low, chemical reactions at the surface of a dust particle can create organics that could be a cradle of life. Being glued up to a meteorite, stardust can reach the Earth. As for its origin, you know stars’ atmosphere includes heavier elements. The gas flowing out a star expands, losses its temperature and eventually comes down to a condensation point, creating clusters of molecules. Now, particles of stardust formed this way can be easily identified due to unusual isotopic composition as compared with that on the Earth. This is because they condensate from stars faster then the isotopes are diluted by interstellar matter. One more source of stardust is an explosion of a star. In a month after a supernova, we can register the dust of 1000 Kelvin temperature. Thus heavier chemical elements become in deficit in the interstellar gas because they go to creation of dust. There is no strict division between gas and dust clouds though. Cold — about 20 Kelvin — cosmic dust condensate in large molecular clouds and fills the center of the galactic disk. A grain of stardust can be as small as ten nanometers covered by a layer of ice. Cosmic dust constitute as much as 0.05 percents of the galaxy mass.
On large quantities 🙂