So I was trying to draw Angel Aura with Star's wand shouting "Mega Narwhal Blast" but I'm still getting used to my drawing tablet so that'll have to wait until I can get something decent done with it. :P
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It could be round as well like the other ones. If it would have been hexagonal and faceted, they would have used more colors to show that, like on the Amethyst's gemstone below. The shape is not really clear, so it would be better to not list it, rather than put speculation on the wikia.