[Rockhounds] Elutriation

[Jim Murowchick]

For anyone interested, there was a USGS paper, probably from the 1960's,
that described an elutriation system for mineral separation.  It consisted
of a series of tall (10-15"?) U-shaped glass tubes (oriented vertically),
each with a stopcock at the bottom of the U.  Each glass tube had a smaller
inside diameter than the one upstream, and they were connected in series
with a rubber tube.  At the start, a separatory funnel with a stopcock at
the bottom held water, and was at the highest elevation.  At the outflow
end, a rubber tube from the last U drained into a collection flask.

    With a slow stream of water flowing through the system (feeding into the
separatory funnel, a slurry containing the sample was drizzled into the
separatory funnel.  The heavies collected at the bottom of the first U,
lighter minerals moved on to the second or third U, and the lightest ended
up in the collection flask at the end.  Fine-tuning of the water flow and
gradient controlled the separation efficiency, and the separates were then
emptied through the stopcock at the bottom of each U tube.

I'll try to find the paper, in case anyone wants the specifics, but if
anyone can provide the reference info, I'd appreciate it.

Jim Murowchick