Tafsir of Al-Ma'aarij 70:9

Like wool (al-ṣūf), without qualification, or red, or dyed in various colors; there are differing opinions [on this]. A group has chosen the latter, due to the varying colors of the mountains, for among them are white streaks, red ones, and intensely black ones. When they are crushed and scattered into the air, they resemble al-ʿihn—that is, teased or fluffed wool—just as in [the chapter of] al-Qāriʿah, when the wind scatters it.

According to al-Hasan, the mountains will move with the winds, then collapse, then become like wool, and finally be blown away, becoming scattered dust (habāʾ).