Interstellar dust contains graphite dust, made of pure carbon, along with other materials. Most of this carbon probably:

Question

Quizplus · Accepted Answer

Carbon stars are known to lose large amounts of carbon in the form of dust, which can be scattered throughout interstellar space. This is the most likely source of the graphite dust found in interstellar space. The other options (T Tauri stars, the Big Bang, and supernova explosions) are not known to produce significant amounts of carbon dust that could contribute to interstellar dust.

Interstellar Dust Contains Graphite Dust, Made of Pure Carbon, Along