The Compendium of Caraka 6.1.3.5

6.1.3.5

That of silver is pungent, white, cool, and digests sweet.
That of copper resembles a peacock's neck, is bitter, hot, and digests pungent.
That, however, which looks like guggulu, is bitter with salt,
pungent in post-digestive effect, and cool, is from iron, and is the best of all.
All have the smell of cow urine and are suited for all procedures,
but for the administration of rejuvenatives, the last is superior.
In vāta-pitta, śleṣma-pitta, kapha, and in all three respectively,
the excretions arising from the minerals gold and the like are particularly praised.
During regimens of śilājatu, one must avoid foods causing burning and heavy foods;
at all times, however, one must completely avoid horsegram.
For they, being exceedingly incompatible, are observed in the world
to be the foremost splitters of stone; therefore, their use is prohibited.
Milk, buttermilk, meat soups, pulses, water, urine, and various decoctions
are commended for stirring śilājatu; they should be used after examining the purpose.
There is no curable disease on earth which that called stone cannot forcefully conquer;
administered according to rule at appropriate times, it also grants abundant energy to the healthy.