[Rockhounds] Geology in Progress

[Dennis Buffenmyer]

Nathan Martin wrote:
> Larry,
> Seems as if you made good use of one of the few mild days we have had.  Lets
> hope that we get more of that "beach weather" soon!
>
> One of the things that I find interesting about your observations is that
> the magnetite was on top of the garnet. Based on the relative densities of
> magnetite (~5.15 gm/cm^3) and typical New England garnets like almandine
> (~4.2 gm/cm^3) or grossular (~3.6 gm/cm^3) , I would have expected just the
> opposite.  I wonder if it is possible that strong wave action could turn
> over a density-stratified layer of sand, garnet and magnetite to produce the
> layering that you saw?  I know that bulk granular materials can have some
> pretty unusual properties but I don't really know if what you observed is
> common.  It may be a really unusual occurrence.  Perhaps someone else on the
> list can comment.  Any sand collectors out there care to venture an opinion?
>
>   
Not a sand collector, but could it be a safe venture to make a statement 
that rocks float?? Most farmers know this and dont realize it.
I suspect that it is more likely that the garnet was able to be worn and 
fragmented to a smaller size than the magnetite and so, the smaller 
particles sink and the larger particles float. Try it some time on your 
vibratory lap unit. fill a mason jar full of various size 
grains/pebbles, chips, and invariably, after a long period of time the 
big ones,,,,,, wind up on top
Dennis Buffenmyer