What types of buried treasure (Rikaz) are subject to the Khums (one-fifth tax)?

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The Khums is obligatory on all types of wealth found as Rikaz, including gold, silver, iron, lead, brass, copper, and vessels. This opinion is held by Ishaq, Abu Ubaid, Ibn al-Mundhir, the companions of Ray (Hanafi school), one narration from Malik, and one position from Al-Shafi'i. The evidence is the general wording of the Prophet's saying: "And in Rikaz, the Khums (one-fifth) is due." Furthermore, it is presumed property belonging to non-believers, thus the Khums is due on it regardless of its type, similar to spoils of war (ghanima).