Firstly: Defining Buried Wealth
Rikaz linguistically: is what is buried. The term is derived from the Arabic rakazahu yarkizuhu rakza if one buried something.
Rikaz technically: buried wealth from the pre-Islamic era.
Secondly: The Ruling of Charity on Buried Wealth
Buried wealth is owned by the one who finds it, and a fifth of it is wajib in charity. Consensus has been quoted on this by: Abu `Ubayd al-Qasim ibn Sallam, Ibn al-Mundhir, al-Baghawi, Ibn Qudamah, and Ibn Taymiyyah.
Thirdly: The Wisdom of a Fifth in Buried Wealth
A fifth is legislated for charity on buried wealth due to the ease of its extraction without an excessively strenuous process, plus its great benefit for those receiving it.
Fourthly: Buried Wealth Being Specifically Pre-Islamic
Buried wealth is specifically that which is buried in the pre-Islamic era.  Difn is madfun – that which is buried. Ibn Qudamah said: “This is considered as so when their signs are clear on what is uncovered, like the names of their kings, their images, their crosses and idols, and the like.” Al-Mughni (48/3) Ibn `Uthaymin said: “Jahiliyyah refers to that which is before Islam, and buried wealth is to uncover some valuables that belonged to those before Islam, recognised by their symbols or a pre-Islamic date, or the like.” Al-Sharh al-Mumti`(88/6) This is the position of the majority: Malikis,  Buried wealth for the Malikis is what is buried in the land of the Arabs from the pre-Islamic era. They also included what is in Muslim-owned lands gained without war. Shafi`is, Hanbalis, and the chosen position of Ibn Hazm.
Fifthly: Gold and Silver as Condition
It is not a condition for buried wealth that it be gold or silver. Rather, all that is discovered has a fifth of it given in charity: gems, gold and silver, lead and copper, iron, etc. This is the position of the majority: Hanafis,  Hanafis did not condition that buried wealth be gold and silver, but they conditioned that it must be every solid that can be moulded under heat treatment, like brass and copper. This is to exclude liquids or powder, like petroleum, bitumen, or salt, and solids which cannot be moulded, like stones, jewels, and gems, where there is no charity payable over them. Malikis, Hanbalis, and the old position held by al-Shafi`i.
Sixthly: The Nisab of Buried Wealth
There is nisab for buried wealth; its abundant has charity given from it. This is the position of the majority: Hanafis, Malikis, Hanbalis, and the old position held by al-Shafi`i, as well as the position of the majority of scholars.
Seventhly: The Passing of a Calendar Year
It is not a condition that a calendar year passes for charity on buried wealth to be wajib. Consensus has been quoted on this by: al-Mawardi, al-Baghawi, al-Nawawi, al-`Iraqi, Ibn Hajar, and al-Shawkani.
Eighthly: Where Charity on Buried Wealth is Spent
Charity paid on buried wealth is spent on the interests of the Muslims. It is not exclusive to the eight avenues where charity is normally paid. This is the position of the Hanafis, Malikis, Hanbalis, a position among Shafi`is, and the chosen view of Ibn Hazm.