The crystal structure of cordierite has many similarities to that of beryl; indialite, the dimorph, in fact has the same structure as beryl. Iolite with hematite inclusions (bloodshot iolite) comes from Sri Lanka. The inclusions sometimes yield a gem showing a 4-rayed star (quite rare). The blue color of iolite along one optical direction strongly resembles sapphire, and such gems, correctly oriented in settings, are often confused with sapphires. Iolite is not a very rare material, but stones that are completely clean over 10 carats are quite uncommon, and clean 15-20 carat gems are worthy of museum display.
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