(Sarah of the Clue Crew shows a gem.) This term is used for red varieties of the gem corundum
In Burma where the term 'pigeon blood' originated, rubies are set in pure 
... Maiman used a solid-state light-pumped synthetic ruby to produce red laser... [DOC] [TLE] ruby - Search-ID.com [PAR] Ruby is a pink to bloo red gemstone, a variety of the mineral corundum (
aluminium oxide).