Hexagonal Aquamarine and Coral. As noted above, it is an interesting combination of a crystal gemstone and an organic gemstone, of a translucent blue and a solid orange-red.
Coral is a gemstone completely unto itself, one of a small number of non-crystalline gemstones that have nothing much to do with each other, aside from their being non-crystalline, uncommon and historically both appreciated and valued; Pearl and Amber, along with “noble” Coral, are probably the best known organic gemstones.
Aquamarine is crystalline, as are most gemstones, and considered semi-precious – Ruby, Emerald, Sapphire and Diamond are the precious – but are among the more rare crystalline gemstones, and of a particularly lovely, cool, translucent blue that has always been appreciated.