'Silver' in the Bible

Thus says the Lord,“For three transgressions of Israel and for four (multiplied delinquencies)I will not reverse its punishment or revoke My word concerning it,Because they sell the righteous and innocent for silverAnd the needy for the price of a pair of sandals.

So that we may buy the poor [as slaves] for silver [since they are unable to support themselves]And the needy for a pair of sandals,And that we may sell the leftovers of the wheat [as if it were a good grade of grain]?”