SB 8.6.35
nipatan sa giris tatra
bahun amara-danavan
curnayam asa mahata
bharena kanakacalah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The mountain known as Mandara, which was extremely heavy, being made of gold, fell and smashed many demigods and demons.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
By constitution, gold is heavier than stone. Since Mandara Mountain was made of gold and was therefore heavier than stone, the demigods and demons could not properly carry it to the Ocean of Milk.