Friday, August 27, 2010

Magnetic Sand

A couple of weeks ago I went down to the beach in Aptos with my son.  Charlie had a magnet with him that he had been playing with as we walked out of the house.  When we got to the beach and started walking out over the sand, Charlie saw what looked like a piece of metal, and he reached down to pick it up by the magnet.  To our astonishment a bunch of sand jumped up onto his magnet.  "Whoa," we said in unison.

To some readers of this blog it may not be new information that there is a lot of magnetic sand in the beaches of California.  The material is magnetite, Fe3O4, a non-rusty oxide of iron.  It is surprisingly fun to collect the stuff, and with a good magnet you can collect five or ten pounds in an hour.  It's also very satisfying to purify it, which you can do by spreading it out thinly on a clean surface, then sucking it up with the magnet, and throwing away what's left.  Two passes of this process leaves you with a pure black almost satin smooth substance.

Of course it's fun to see how the sand stands up in needles when there is a magnet below (or above), but I'm trying to think of something *truly cool* to do with it.  I first thought that if I put it inside a plastic pipe I could get it to run along inside by activating coils along the pipe, but it's not that simple.  You would think (at least I did) that the stuff would just behave like the core of a solenoid, and jump into any coil.  But it's sand, so it is more interested to stretch itself out along the magnetic lines of force than it is to jump to the center of the coil.  Since this blog is supposedly a two-way thing, I'm curious if any of you/us know of, or can think of, something incredibly cool to do with this stuff.

If you live on the west coast (I can't vouch for the east coast), by all means take a magnet with you next time you're headed for the beach, and see what you find.  Look for darker patches (especially on dunes where the wind preferentially blows the lighter silica away), and come to Aptos if you are stuck.  A geologist who stopped by told me that the beach at Fort Funston has especially high magnetic sand content.

Have fun.

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