You might think these are imaginary elements, like lathium or dilithium crystals, but rhenium and iridium are real. You can find them on the periodic table. Rhenium is so dense that a "tooth sized" piece weighs over ten pounds. Only platinum, iridium and osmium are denser. It is so rare it costs $11,000 per kilo, and makes up no more than four parts per billion of the Earth's crust. Rhenium was the last naturally occurring stable element to be discovered and is among the ten most expensive metals on earth.
Rhenium was first identified in 1925 in Platinum ore and the mineral columbite. However, it was so expensive to extract, it was abandoned and ignored until 1950 when it was alloyed with molybdenum and tungsten.
In appearance it is a silvery-white metal. Mixed with other alloys it is used in jet engines as it can withstand the heat and pressure and is the most efficient material. About 35 kilograms are needed to construct one Jet engine. Obviously, with this usage, one would not be surprised to learn it has one of the highest melting points, exceeded only by tungsten and carbon. It has the widest range of oxidation states of any known element.
It's usual commercial form is a powder, but it can be pressed in a vacuum or hydrogen atmosphere into a shape. Besides it's use in jet engines it is also used in platinum- rhenium catalysts which make lead free high octane gasoline. Chile has the largest reserves of this mineral. However, the total world production is just about fifty tons a year.
Another very important and barely known element is Iridium which resembles Rhenium. It is a high-strength alloy that can withstand high temperatures and occurs in natural alloys with platinum or osmium. It's claim to fame is that it is the most corrosion-resistant element known.
Further, Iridium has a particular place in history; it is believed the asteroid which hit the Earth about sixty five million years ago was made of Iridium.
The temporal border between the Cretaceous and Tertiary periods of geological time, was identified by a thin stratum of iridium-rich clay. This is believed to be of extraterrestrial origin. Iridium is used in high-temperature apparatuses, electrical contacts, and as a hardening agent for platinum. One of its actual uses is in supercolliders in the production of antimatter, specifically antiprotons.
