Is it permissible to donate Zakat funds for decorating the mosque, and is what is given for purposes other than Zakat considered an ongoing charity (Sadaqah Jariyah)?

It is not permissible to spend zakat on building or adorning mosques, as the recipients of zakat are specified in the Quran. However, constructing mosques and assisting in their construction is an ongoing charity (sadaqah jariyah). If the purpose of using marble is for ornamentation and beautification, then this is a luxury, and it is more befitting to participate in building mosques, digging wells, or similar acts of worship that carry immense reward.