Iridium is a rare and expensive corrosion-resistant metal that has a variety of uses in different industries. Below are some common uses of iridium:

1. Spark plugs: Iridium is used in the manufacture of high-performance spark plugs because of its high melting point and low reactivity.

2. Crucibles: Iridium is used to make crucibles for recrystallization of semiconductors at high temperatures. It is also used in the construction of crucibles or containers for melting and manipulating other industrial metals.

3. Catalysts: Iridium is used in industrial catalysis as an important component of some OLEDs. It is also used in catalysts for some chemical reactions, for example, the hydrogenation of ethylene to ethylene glycol.

4. Armor plating and knife blades: Iridium is used to strengthen materials for armor plating and knife blades.

5. Electronics: Iridium is used in the electronics industry as it resists corrosion. It is often used in electronics because of its high tolerance to heat.

6. Atomic weapons and satellites: Iridium is used in the production of neptunium and plutonium isotopes for atomic weapons and satellites.

7. Communication: Iridium is often used in nuclear energy applications. For example, reactor fuel is alloyed with iridium.

Iridium is also used in fountain pen nibs, compass bearings, and the international prototype meter stick.