Padparadscha, the pink-orange gem named for a lotus blossom, is a variety of which mineral?

Corundum - the same mineral as ruby and sapphire, which are chemically identical aluminium oxide differing only in trace impurities. Chromium makes it red and it is called ruby; anything else and it is called sapphire, in any colour including colourless.

Padparadscha is the pink-orange one, from the Sinhalese for lotus blossom, and it is among the most valuable and the most argued-over. Where exactly pink stops and orange begins is a judgement call, laboratories disagree, and a stone certified as padparadscha can be worth many times the same stone certified as a pink sapphire - so a colour boundary with no physical basis carries a large amount of money.

Corundum is also the hardest common mineral after diamond, which is why the same substance is sold as gemstones and as sandpaper grit. Synthetic corundum has been mass-produced since 1902 by a flame process, is chemically indistinguishable from the natural stone, costs almost nothing, and ends up in watch bearings, laser rods and phone camera covers - the gem trade depends entirely on distinguishing origin rather than substance.