What is taken into account is the weight of gold or silver contained in the jewelry. As for any pearls or similar materials it may contain, they are not counted toward completing the minimum taxable threshold, nor is zakah due on the pearls or similar materials within it, because they are neither gold nor silver. Jewelry made from materials other than gold and silver is not subject to zakah unless it is held for trade.
But is the relevant standard for the gold threshold the Islamic dinar, whose weight is one mithqal, and for the silver threshold the Islamic dirham, whose weight is seven-tenths of a mithqal? Or is the relevant standard the dinar and dirham as customarily recognized in each time and place, regardless of whether the gold or silver they contain is little or much (1)?
The majority hold the first view, and it has been reported as a consensus.
Shaykh al-Islam Ibn Taymiyyah established the second view: namely, that the relevant standard is the dinar and dirham conventionally recognized in each time and place. Thus, whatever is called a dinar or a dirham is subject to the rulings attached to the terms dinar and dirham, whether the gold or silver it contains is little or much. This is, in my view, the stronger opinion, because it accords with the apparent meaning of the textual evidence. Accordingly, the threshold for gold is twenty junayhs, and the threshold for silver is two hundred riyals. Yet if a person takes the cautious course and follows the view of the majority, he has done something for which he will be rewarded, if Allah wills (2).
(1) The Islamic dirham weighs less than the dinar: a dinar is one mithqal, whereas a dirham is seven-tenths of a mithqal. Thus, ten Islamic dirhams equal seven mithqals, while ten dinars equal ten mithqals. This means that, in the time of the Prophet, peace and blessings be upon him, the dirham was lighter than the dinar. In our present usage, however, the dirham is much larger than the dinar.
A dinar is a gold currency, and a dirham is a silver currency. In our terminology, the dinar is called a junayh (pound), and the dirham is called a riyal.
(2) The more cautious approach is to adopt the lower threshold; that is, whichever first reaches the nisab (minimum taxable amount). For example, if two hundred dirhams are estimated not to reach one hundred and forty mithqals when calculated by weight, which is the view of the majority, then the more cautious approach is to calculate by number, since two hundred dirhams reach the nisab numerically but not by weight. If, however, two hundred dirhams are estimated to exceed one hundred and forty mithqals—amounting, for example, to two hundred mithqals—then the more cautious approach is calculation by weight, which is the view of the majority.
At present, the nisab by weight is fifty-six riyals, whereas by number it is two hundred dirhams, which is approximately one quarter of the nisab by weight. The ratio of fifty-six to two hundred is slightly less than one quarter. In any case, we follow the more cautious view, in consideration of those entitled to zakah: if the nisab is reached by number before it is reached by weight, we adopt the view of Shaykh al-Islam Ibn Taymiyyah, since it is more cautious; and if it is reached by weight before it is reached by number, we adopt the view of the majority, since it is more cautious.