[Rockhounds] Trip Report - Denver Area - ilsemannite

[Pmodreski at aol.com]

Yes, you even spelled the mineral name correctly, Earl!
 
This was, of course, the same roadcut you are familiar with.   Ilsemannite is 
an odd mineral, a hydrated molybdenum oxide, I'll look up the  formula, it's 
Mo3O8+nH2O (?)   (the plus sign will represent the "dot"  that I don't think I 
can type into the email program; and note the (?) appended  to the formula; 
it's basically a non-crystalline material, probably should be  considered a 
"mineraloid", not a true crystalline mineral--call it the  molybdenum equivalent 
of limonite).  It occurs as inky-blue stainings and  encrustations on certain 
layers of the sandstone, where ground water seepage has  carried molybdenum to 
the surface.  One sees no crystals; where there do  appear to be crystals, it 
is generally crystals of gypsum or some other sulfate  mineral that have also 
formed there, and the ilsemannite has simply deposited on  the surface of 
those crystals (like in the old-time salt-crystal-growing rock  garden, such as I 
always made in a fish bowl when I was a kid, where you put  lumps of coal in 
the bottom, sprinkled salt on them and some water, and added  "Bluing" for 
color; Earl, I'll bet you did that too.).  The ilsemannite is,  I have read, 
basically a colloidal material, and will wash away into a  suspension in water 
when it becomes wet.
 
Pete
 



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