This is the 6th verse of Ghalib’s 20th ghazal
Rag-e-sang se tapakta, woh lahu ke, phir na thamta
Veins of rock would have gushed blood, unstoppable
Jise Gham samajh rahe ho, yeh agar sharar hota
if its sparks were sparks of my (love) agony instead
Rag = Vein, artery,. sang=rock, stone., Rag-e-sang = Veins or lines of a rock/stone; Ghalib compares them with human blood veins
Meaning: Ghalib postulates, sparks are hidden in rocks as blood is in body. Since sparks are red, poet calls them blood of rock. He says if red sparks of rocks were sparks of my love-anguish, veins of rocks would have gushed unstoppable blood torrent. Meaning anguish of love is so excruciating even rocks cannot bear; only my heart has power of containing it. If such anguish had befallen on rocks, it would have gushed unstoppable blood (sparks).