An unusual piece of lava rock very blue in true color.
Mike - this one appears to be Chalcedony, also spelled Calcedony, a very fine-grained (cryptocrystalline) variety of the silica mineral quartz. The blue colorization is typical in that variety of quartz. Coming from a volcanic parent rock I would almost bet you that if you blacklight this piece it will fluoresce a bright "lime green". Fairly common secondary low temperature mineral in volcanics. Is a close cousin to opal.
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