Now corundum is a fairly common mineral.
Are rubies rare.
In nature diamonds are rare but not so in the gem world.
Forget diamonds emeralds and rubies.
Ranking a 9 on the mohs scale of hardness diamond is a 10 corundum has been mined extensively for abrasives.
All rubies are rare but those from myanmar formerly burma set the standard for quality and color.
They are also exceptionally scarce.
The emery on your emery boards and sand paper may contain.
While rubies from thailand contain relatively high iron content which can result in overly dark reds with brownish or purplish overtones the geological conditions in myanmar generally produce rubies with very little trace iron.