fayʾ, and it is not limited to the eight designated categories.

9 – Hadith (515) indicates the following:
If buried treasure (rikāz) is found in uncultivated land, communal land, land whose owner is unknown, on the surface of ownerless land, on an unused roadway, or in an abandoned village, then in all these cases it belongs to the finder. The same applies if the finder notifies the present landowner and the property had come into that owner’s possession after the treasure was buried: it still belongs to the finder unless the owner lays claim to it. If the owner does claim it but produces neither proof nor an identifying description, the rikāz is awarded to the landowner once he swears an oath, for the owner’s “hand” extends over the land and therefore over what lies in it, giving his claim priority.
The same ruling holds if someone from whom the land formerly passed claims it, for his “hand” once covered the land as well.

10 – Hadith (516) establishes that zakāh is obligatory on minerals. Minerals are naturally occurring inorganic substances possessing a definite chemical composition and specific physical properties; they are made up of the same chemical elements—such as gold, iron, brass, and mercury—and are generated from the earth though not of its own essence.

11 – The hadith shows that zakāh on minerals becomes due only when the recognized niṣāb is reached. That niṣāb is twenty mithqāls of gold, two hundred dirhams of silver, or their cash equivalent in other substances such as iron, copper, lead, crystal, agate, and the like. Once this threshold is met, zakāh is payable immediately, in keeping with the general wording of Allah’s statement, “and spend of that which We have brought forth for you from the earth” (Q 2:267).

12 – The rate is one quarter of one tenth (2.5 %), because extraction incurs effort and expense.

13 – Different mineral types are not combined to complete the niṣāb, even when they are closely related, such as tar, petroleum, iron, and copper.

14 – By consensus of the four schools, the zakāh is paid as soon as the mineral is obtained, for it is wealth newly acquired from the earth and therefore not subject to the passing of a lunar year. If what is extracted is less than the niṣāb, no zakāh is due.