Complex sentence: In some cases, a government may stamp a metal coin with a face value or mark that indicates its weight or asserts its purity, but the value remains the same even if the coin is melted down.
Split into simpler sentences: In some cases, a government may stamp a metal coin with a face, value or mark that indicates it's weight or asserts it's purity. But the value remains the same even if the coin is melted down.