Sackcloth, or haircloth
Archimandrite Nikifor’s Biblical Encyclopedia
(Rev. 6:12) — a coarse, dark-colored fabric, made from goat’s hair. From this fabric were made sacks (Gen. 42:25), as well as garments worn by men and women as a sign of mourning (1 Kings 21:27; 2 Kings 6:30; Job 16:15; Isa. 32:11; Jonah 3:6; Joel 1:8; 2 Macc. 3:19). This garment was, it seems, of the simplest form, resembling a sack. Sackcloth was sometimes girded with a belt of the same fabric (Isa. 3:24); sometimes, in special mourning, it was also worn at night (1 Kings 21:27 [as given]).
Scripture cited
Revelation 6:12Genesis 42:253 Kingdoms 21:274 Kingdoms 6:30Job 16:15Esaias 32:11Jonas 3:6Joel 1:82 Maccabees 3:19Esaias 3:24