#MinCup24 Corundum vs arsenuranspathite: it's great that nature can bring enough fluorine, arsenic and uranium and aluminium together to grow crystals of arsenuranospathite, but it's got to be #Corundum for me! Here's Scotland's greatest gemstone: the 9.8ct "Saltire Sapphire" (the blue variety of corundum) from Loch Roag in Lewis, found and cut by Ian Combe, now in the collections of National Museums Scotland, in Edinburgh 🥰 🤩 #Geology #Mineralogy #Corundum