Purple Gems can be used to power Winona's G.E.M.erator (though it is more efficient to use Blue or Red Gems for this purpose since they can be easily acquired on the surface). They're also used for several other character-specific recipes and useful gear. See below for a full list.
Obtained by inserting the Gem into the Cratered Moonrock.
×10
×4
Tips
Thanks to periodic Hound waves, purple gems are renewable, even in the base game, as both Red Hounds and Blue Hounds drop Red and Blue Gems, respectively.
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