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3D3DNiobium crystal bar.
From the source:
This is a sample of niobium crystal bar, produced by the same basic method as the Van Arkel/de Boer (Iodide) crystal bar process used to purify hafnium, zirconium, titanium, and occasionally thorium, though with different chemical precursors and reaction conditions in order to adapt the process to niobium.

Some of you may be scratching your heads, saying "But I thought the iodide crystal bar process was only used for the metals just mentioned--I've never heard of it being used for niobium." Pat yourselves on the back--you're 100% correct. This piece of niobium crystal bar is, as far as I have ever heard, one of only three or four small pieces in the world, leftover from an experiment on niobium reduction and purification performed about 45 years ago. Some more was produced, but the rest was melted down. If you have any information about this experiment or another like it, please email. I am not sure of exactly what they did, but from how the bar is half-melted, I would guess that the crystal bar was produced, cleaned, and vacuum induction melted into a round bar before it was to be zone-refined and then analyzed for final purity.

Most importantly, though, look at those fabulous crystals. Niobium is a very tough, hard metal that is extremely chemically resistant- left to its own devices on Earth, those beautiful crystalline facets would likely last millions of years, unless they were subducted into the mantle or happened to be in the direct path of a volcanic eruption.

Source: Ethan Currens
Contributor: Theodore Gray
Acquired: 27 December, 2008
Text Updated: 1 March, 2009
Price: Anonymous
Size: 1.5"
Purity: >99.99%