77 Iridium - Ir

Iridium is a hard, brittle and silvery-white transition metal of the platinum group.
Because it is found in meteorites, an usually high abundance of iridium in the clay layer at the Cretaceous-Paleogene boundary gave rise to the hypothesis of the impact that caused extinction of dinosaurs.
A similar anomaly in core samples from the Pacific Ocean suggested the Eltanin impact about 2,5 millions years ago.
It is the second most dense metal, the first one is osmium.
The most important properties and uses are the high melting point and the hardness.

Where can be found:
Iridium can be found in meteorites in much higher abundance than in earth's crust.
Natural iridium often contains Os, Ru or Pt.
Often incorporates mineral species as osmiridium, ruthenosmiridium.
Minerals: Changchengite, Cuproiridsite, Gaotaiite, Inaglyite, Irarsite, Iridarsenite, Kashinite, Malanite, Mayingite, Shuangfengite, Tolovkite, Xingzhongite
It is often found with a composition of iridium 52%, osmium 31%, Ruthenium 5% and platinum 10%
Can be found in sparkplugs, particulary aviation.
Iridium can be found in meteorites and asteroids.
Iridium can be found in corrosion resistant compasses, alloyed with osmium as pivot point.
Iridium can be found commonly in phonograph needle having a purity of ~50%.
Spark plug - because its survives a long time under harsh conditions.

Properties:
Atomic number 77; Atomic weight 192,217
solid at 20 C
Melting point of 2446 C
Boiling point 4130 C
Density 22,56 g/cm cube
Crystal structure: face-centered cubic / isotropic
Speed of sound 4825 m/s at 20 C
Magnetism: paramagnetic
Hardness: 6-7
Streak white
Color white, opaque, metalic, silver
Electrical type: conductor
Non fluorescent
Luster metallic
0,000054% abundance in meteorites
Isotopes from Ir 164 to Ir 199 with stable isotopes: Ir 191 and Ir 193
Ir 191 has 37,3% abundance
Ir 193 has 62,7% abundance

Minerals: Iridospine - osmiridium

Common impurities: Pt, Au, Pd, Cu, Fe
Common associates: Osmium, Osmiridium Isoferroplatinum, Iridosmine, Rutheniridosmine, Chengdeite, Ferronickelplatinum, Laurite, Iridian tulameenite, gold

Uses:
It is used in compounds as salts and acids.
Has a high corrosion resistance and used as spark plugs etc.
It was used as iridium-osmium alloy in fountain pen nib tips.
The tip material in modern fountain pens is called conventionally iridium but rarely that is true, other metals like ruthenium, osmium and tungsten taken its place.
It is used as alloys with platinum or osmium.
Osmium-iridium is used for compass bearing and for balances.
Iridium is used as coating for scanning electron microscopes.
Iridium has been used in the radioisotope thermoelectric generators of unmanned spacecraft like Voyager, Viking, Pioneer, Cassini, Galileo and New Horizons; chosen to encapsulate plutonium 238 fuel and withstand the operating temperature of 2000 C.
The mirror of Chandra x-ray observatory is coated with layer of iridium 60 nm thick for the best reflecting x-ray after nickel, gold and platinum; the layer had to be smooth to within a few atoms.
Iridium is used in particle physics to produce antiprotons and antimatter. Made by shooting high-intensity proton beam at a target that needs to be made from a very high density material. Tungsten may be used but iridium has a better stability under shock waves induced by the temperature rise.
Iridium was used very common in phonograph needle to last long time.

Iridium tips in pens:
They have a composition that ranges from:

• iridium 54%, osmium 44%, silver 0,70%, copper 0,50%, gold 0,24% with possible traces of Ruthenium
• Earliest Parker nib tipping: Osmium 44,3%, Iridium 34,8%, Ruthenium 20%
• 1920 Parker Duofold Sr: Osmium 85,3%, Platinum 5,9%, Tungsten 4,51%, Ruthenium 2,01%, Copper 1,84%
• a second 1920 Duofold: Rhodium 43,6%, Ruthenium 19,3%, Gold 17,4%, Osmium 6,9%, Tantalum 6,8%, Copper 5,3%, Iron 0,7%
• pen around 1924: Osmium 96,6%, Rhodium 3,4%
• Parker Duofold: 1927 29% Ruthenium, 38% Osmium, 33% Iridium
• A 1940 Duofold: Osmium 58,2%, Tungsten 41,8%
• Parker 51 1952: 2,6% iridium
• Parker 51 1956: 100% Ruthenium
• Parker 51 1957: 56% Ruthenium, 44% Rhodium

Most of tip pens after 1950 are fake.
Most of them use osmium, rhenium, ruthenium and tungsten instead.
Today nibs are made of stainless steel or gold alloy.

Isotopes:
188: synthetic, half-life 1,73 days, decay ε , product osmium 188
189: syn, half-life 13,2 days, decay ε , product osmium 189
190: syn, half-life 11,8 days, decay ε , osmium 190
191: abundance 37,3%, stable
192: syn, half-life 72,827 days, decay beta minus with product platinum 192 and decay ε with osmium 192 product
192m2IR: syn, half-life 241 years, decay IT; product iridium 192
193: 62% abundance, stable
193m: syn, half-life 10,5 days, decay IT, product iridium 193
194: syn, half-life 19,3 hours; decay beta minus; product platinum 194
194m2Ir: syn, half-life 171 days, decay IT; product iridium 194

Iridium compounds, minerals, isotopes, main ions, associated elements: https://www.mindat.org/element/Iridium
In-deph info: https://periodictable.com/Elements/077/data.html