Case 1: silver predominates
The silver nisab rules apply; a minor admixture does not change its principal substance.
Case 2: base metal predominates
The rules for goods and their value become relevant, especially where the property is trade inventory.
Important qualification
If the extractable pure silver still reaches its own nisab, the silver liability remains relevant.
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Zakat on Silver: Nisab, Incremental Dues and Alloyed Dirhams
Case 1: silver predominates
The silver nisab rules apply; a minor admixture does not change its principal substance.
Case 2: base metal predominates
The rules for goods and their value become relevant, especially where the property is trade inventory.
Important qualification
If the extractable pure silver still reaches its own nisab, the silver liability remains relevant.