There's a mineral so rare that only one specimen of it has ever been found in the entire world.
"It's called kyawthuite (cha-too-ite), a tiny, tawny-hued grain weighing just a third of a gram (1.61 carats). On first glance, you might mistaken it for amber or topaz; but the unassuming mineral speck has value beyond measure."
You caught me. I'm a terrible lying liar who only says things like this to impress people on the internet by making them think I did something stupid instead of something else stupid. It's all part of my fiendish plan to make people think I'm an idiot. You found me out. Curses!
It's all good, if you didn't get it wronf, none would have corrected you and 99/100 that didn't read the story wouldn't know. You provided us 35 seconds of insight second hand.
Guy found an interesting rock in a gemstone market in Myanmar, thought it was one thing, made it pretty, found out not only was it something else, it was something never before seen in nature.
I only read the above comment up to 'tldr' and skimmed the rest so the tldr is that the world's rarest mineral is so rare that it's only ever been found once!
Like the guy who cut down the oldest know tree to find out how old it was. It wasn't known how old it was at the time. (They have found probably older but don't want to cut them down to find out.)