Rubies are super hard!

My birthday is very, very soon, it's the 7th of July and I will be 18 finally!
Did you know that rubies are the birthstone for July? ...ok so you probably did, but me being the ChemNerd that I am I thought I would look into the chemistry behind rubies.

Rubies are the most stable form of corundum, which is a crystalline form of aluminium oxide (Al2O3), if the corundum is red it gets called a ruby, if it is ANY other colour it is called a sapphire!

So with a ruby's colour, what happens is some of the Al3+ ions are replaced by Cr3+ ions and each chromium ion has six O2- ligands, which cause an energy jump in the d-orbital electrons, which results in the absorption of yellow-green light giving the gem a red colour! In other terms what happens is the six oxygen ions surround the chromium ions and give them their spare pair of electrons, which affects the chromium's electrons, which results in the colour absorption.
This diamond ring from Tiffany & Co. costs £4,552,500... (feel free to buy it for me)
Ok, you know how diamond is like the hardest thing in the world, well its got an Moh mineral hardness of 10.0, and rubies are the 3rd hardest mineral with an Moh of 9.0, so they are pretty damn hard.