Mithril:

A metal found only in Khazad-dûm, it was highly prized by the Atani, the Eldar, and the Dwarves. Sauron coveted it and did his best to collect it all. Mithril was called True-silver and many other names. It could be forged into a light hard substance like steel, it had the shine of silver but never tarnished. After the discovery of the Balrog, when Khazad-dûm was abandoned and gained the name the Mines of Moria, most of the Mithril was gathered by the goblins and orcs inhabiting Moria and given to Sauron in tribute. By the end of the Third Age of the Sun, the only mithril items known (or named) were Bilbo's dwarf mail, the Elven Ring, Nenya, the helms of the Guards of the Citadel of Minas Tirith. Mithril had many uses including Ithildin, as seen on the gates of Moria.

Mallorn:

Mallorn trees had silver trunks and golden leaves and flowers. The leaves stay on the trees until spring, when the wood becomes roofed and floored with gold, with silver pillars. The only places in Middle-Earth that Mallorn Trees grew were Lothlórien and later one grew in the Party Field in the Shire. This single Mallorn was the gift of Galadriel to Sam Gamgee, and it was the only Mallorn west of the Mountains and East of the Sea.

Mallos:

A golden flower known to grow in Lebennin.

The Lord of the Rings
The Silmarillion
The Unfinished Tales
The Hobbit
The Complete Guide to Middle Earth by Robert Foster