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3DVery Odd Lump.
This is a strange-looking lump of solid pure boron. It has several different kinds of surfaces, as you can see if you click on the picture to see the large version. I would love to know more about the means by which this lump was made.
Reader Graham Cowan offers the following theory:
From the bottom of p. 4 of this pdf file:
"In 1985, Callery repurchased reserve pentaborane fuel from the military and reprocessed it into elemental boron. When this became unprofitable ..."
Pentaborane, B5H9, is like all B-H compounds unstable with respect to dissociating into B and H2, so the only processing necessary would have been to heat it in the absence of air and water. (Probably in argon.)

Your nice big photo shows nodular surfaces and fracture ones. I think the nodular surface is where the gaseous BH stuff laid boron down on the hot lump.

--- Graham Cowan
Here is his interesting page about boron as a fuel.

And as you can see below, this lump was considerably more cost effective than our first attempted sample.
Source: David Franco
Contributor: Ed Pegg Jr
Acquired: 16 August, 2002
Text Updated: 11 August, 2007
Price: $12
Size: 0.5"
Purity: 99.9%