What is the ruling regarding the prayers I performed with tayammum on a tile surface that I thought was natural, but later discovered to be artificial, and must I repeat them?

Performing tayammum (dry ablution) on marble tiles and the like is not valid. All prayers performed with such an invalid tayammum must be re-offered. If the number of such prayers is unknown, one must continue re-offering them until it is highly probable that one's obligation has been fulfilled. This is the view of the majority of scholars. Some scholars, such as Ibn Taymiyyah, held that whoever omits a condition or a pillar out of ignorance is not required to repeat the prayer.