A FASCINATING and rare old German specimen that came out of the Harvard Mineralogical Museum collection (comes with label). You can see clearly the cubic forms of the crystals. But if you look inside, you see that they are QUARTZ, which of course does not form these cubes; the guess of the Harvard curators is that they were originally fluorites, completely replaced by quartz, and then later cast and coated with limonite (which gives the surface their brownish color). Ex. Harvard and Elling collections.