Ah! The Corundum Conundrum; isn't that a perfect mineralogical riddle for this age of the Dum-Dum?! Corundum, as well as the lollipop, occurs in a wide variety of colors.
Corundum is the crystalline form of aluminium oxide, Al2O3, generally containing traces of iron, titanium, vanadium and/or chromium. The blue, green, orange, yellow, purple and clear gem varieties are all sapphires.
And, new to me, the pink-orange exotic gem variety is named padparadscha. The word is derived from the Sanskrit or Sinhalese padma raga, meaning “lotus color” and refers to the pink-orange color, similar to the lotus flower. Natural padparadscha is among the rarest and most highly prized varieties of corundum.
The word "corundum" is derived from the Tamil word Kurundam which originates from the Sanskrit word kuruvinda meaning ruby.
Because of corundum's hardness (corundum has a hardness of 9.0 on Mohs hardness scale), it can scratch almost every other mineral, except diamond. The hardness of corundum is 1/400 that of diamond.

Corundum is used as an abrasive in sandpaper and in machining metals, plastics, and woods.
Corundum belongs to the hexagonal crystal group (Recall the PEOTS post on Sapphire of the Sea).
In addition to its hardness, corundum is very dense at 4.02 g/cm^3, which is very high for a transparent mineral composed of the low-atomic mass elements of aluminium and oxygen.
Atomic numbers of 13 for aluminum and 8 for oxygen, both Fibonacci numbers, can't be a corundrum conundrum coincidence, can it?
Let's see, hard, very dense, and colorful: where have we heard that corundum conundrum before? Riddle me Ruby? Dumped on by the Dum-Dums?
Happy Colorful (not Black) Friday from the wonderful colors of Zoë and friends in Ethiopia!
Very Thankfully,
Steph
