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For years growing up I thought cobalt was radioactive. This probably had something to do with the Planet of the Apes movies, and the fact that a radioactive isotope, cobalt-60, is widely used in medicine. Of course nothing of the sort is true: Cobalt is perfectly stable, and not even particularly toxic.
It's commonly used as an alloying element with iron (cobalt steel tool bits, etc). It's also a component of special alloys used for artificial body parts, but is rarely used in pure form.
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  Anode button.
Purchased from Neil Lipson (Lipson@postoffice.att.net) after contact through eBay. I'm very unclear on what process this odd item was a result of, but clearly electro-accumulation is a reasonable claim. It's quite peculiar. I have a pound of very similar buttons made of nickel instead.
Source: Neil Lipson
Contributor: Theodore Gray
Acquired: 29 May, 2002
Price: $5
Size: 1.25"
Purity: >99%
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Another anode button.
This one was donated by David Franco in exchange for Mathematica T-shirts. It's similarly peculiar.
Source: David Franco
Contributor: David Franco
Acquired: 11 June, 2002
Price: Donated
Size: 1.25"
Purity: >99%
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Top of knee joint.
This is the top of an artificial knee joint: I've removed the plastic block that attaches just underneath this metal part, and which mates with the double-ball of the other half, which you can see under aluminum. Unfortunately they seem to be a different brand or something because the parts don't fit each other.
I originally thought these were titanium, but the source, Paul Wellin's Brother, reports as follows:
"The top of knee joint and the hip joint ball attachment are probably made of a different alloy, cobalt-chrome, for increased strength and decreased flexibility as compared to titanium."
I don't know whether there is more cobalt or more chromium in the alloy, so I've somewhat arbitrarily chosen to put them under cobalt.
Source: Paul Wellin
Contributor: Paul Wellin
Acquired: 14 June, 2002
Price: Donated
Size: 2.5"
Purity: <60%
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Hip joint ball attachment.
This is the part of an artificial hip which is inserted into the long bone of the leg, whatever that's called. Then a ball screws onto the end of it. The middle section is coated with some kind of rough probably ceramic surface, to encourage bone to grow into and attach to it. The ball fits into a socket which you can see under titanium.
Source: Paul Wellin
Contributor: Paul Wellin
Acquired: 14 June, 2002
Price: Donated
Size: 5"
Purity: <60%
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Odd-shaped nodule.
You can always count on Lipson for a strange lump of something. Heaven knows where this one is from.
Source: Neil Lipson
Contributor: Theodore Gray
Acquired: 10 January, 2003
Price: $5.50
Size: 2"
Purity: >95%
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Sample from the Everest Element Set.
Up until the early 1990's a company in Russia sold a periodic table collection with element samples. At some point their American distributor sold off the remaining stock to a man who is now selling them on eBay. The samples (excepted gasses) weight about 0.25 grams each, and the whole set comes in a very nice wooden box with a printed periodic table in the lid.
To learn more about the set you can visit my page about element collecting for a general description and information about how to buy one, or you can see photographs of all the samples from the set displayed on my website in a periodic table layout or with bigger pictures in numerical order.
Source: Rob Accurso
Contributor: Rob Accurso
Acquired: 7 February, 2003
Price: Donated
Size: 0.2"
Purity: >99%
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