What is the standard for determining the measure or weight of gold and silver?

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Gold and silver are established as items determined by weight. This is established by the Prophet's saying: "Gold for gold, weight for weight, and silver for silver, weight for weight." Items similar to them among the minerals of the earth, such as iron, copper, brass, lead, glass, and mercury, are also determined by weight. Items like silk (ibrīsam), cotton, linen, wool, and their spun forms are also determined by weight. This includes bread, meat, fat (shamh), cheese, butter, wax, and similar items, as well as saffron, safflower (usfur), and *wurs*.