Shattuckite is a relatively rare copper species that seldom forms good crystals, and in this case, it has actually formed a HUGE and phenomenal crystal as a replacement of a relatively large, pre-existing crystal, probably of quartz or cuprite, resulting in what we call a pseudomorph. The large, 4.5 cm, crystal shows a variegated dark blue and sky blue color because it is actually a composite of both Shattuckite and Chrysocolla. While many pseudomorphs of such large crystals are "mushy" or soft in appearance, these species here have faithfully preserved the shape of the original crystal perfectly! We've gone back and forth as to whether we think this could be quartz or cuprite, but honestly, without destructive testing, it's unknown. A few patches of Chrysocolla and Malachite are also present around the periphery of the piece. It's only one of a small handful of specimens I have seen that even remotely approach this level of quality and the size is ridiculous. These pseudomorphs were never common and they rarely come up for sale, this being the most significant example I have seen in a long time. I was told that these came out of Charlie Key's mining projects initially back around 2005-2010, and no large ones have come out since. Even then, they were rare. Although a replacement of another mineral, still this is a huge shattuckite crystal and must surely be among biggest of species.