SB 8.6.35

nipatan sa giris tatra
 bahūn amara-dānavān
cūrṇayām āsa mahatā
 bhāreṇa kanakācalaḥ
Synonyms: 
nipatan — falling down; saḥ — that; giriḥ — mountain; tatra — there; bahūn — many; amara-dānavān — demigods and demons; cūrṇayām āsa — were smashed; mahatā — by great; bhāreṇa — weight; kanaka-acalaḥ — the golden mountain known as Mandara.
Translation: 
The mountain known as Mandara, which was extremely heavy, being made of gold, fell and smashed many demigods and demons.
Purport: 

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.