The word(s) "dunas" appears 2 time(s) in 2 verse(s) in Quran in Portuguese (Prof. Samir El-Hayek) translation.

(1) Menciona-lhes o irmão de Ad (Hud), que admoestou o seu povo nas dunas, embora já tivesse havido admoestadoresantes e depois dele (que lhes disseram): Nada adoreis além de Deus, porque temo por vós o castigo do dia aziago.

(سورة الأحقاف, Al-Ahqaf, Chapter #46, Verse #21)
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(2) Será o dia em que haverão de tremer a terra e as montanhas, e haverão de se converter, as montanhas, em dunas dispersas.

(سورة المزمل, Al-Muzzammil, Chapter #73, Verse #14)
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