Rockin the Rockies

Rockin the Rockies
Rock Hounding

Saturday, July 27, 2013

Fluorite and Pocket Minerals

Quite often when I find a large pocket of crystals there will be some strange mineralization at the bottom of the pocket. Many crystals are pressure and temperature dependent in the order in which they form. I understand that as the mineralized liquids cool in the miarolitic cavity, some crystals form first and others later.  Minor minerals are pushed aside until the main crystals are formed. I guess what's ever left of the volatile liquids forms the oddities. Sometimes there are later stage intrusions into the pocket of a hydrothermal nature. While hydrothermal intrusions do not occur in all pockets, when they do you can get some odd minerals as well. One of the most common hydrothermal minerals to be found in pockets is fluorite. Also calcite and goethite seems to be quite prevalent. Sometimes the secondary minerals can be found in several areas within a pocket, but often these occurrences appear at the bottom of the pocket. When I've completed the extraction of crystals from a gem pocket, I always excavate the bottom of the pocket just to make sure I haven't missed anything.  The other day while I was finishing up a pocket I ran into some nice green fluorite. So I extracted the in matrix fluorite specimens and began the process of cleaning. While cleaning I noted some rather odd looking secondary minerals, so I took out my microscope and toothpick to continue the cleaning process. While I'm not exactly sure what I have besides fluorite and calcite, there are definitely some odd minerals accompanying the fluorite. I've taken the specimen to a few more experienced rock hounders, and they were scratching their heads over the mineralization as well. One of the guesses for the acicular crystals was bertrandite. http://en.wikipedia.org/wiki/Acicular_(crystal_habit)  Anyway I found that finding the crystals is most of the fun, but figuring out secondary mineralization can be quite a challenge. If anyone has any thoughts on some of these pics, or how to proceed, let me know.  Thanks to my digging buddy Bob for helping me photograph the minerals.
Fluorite in matrix

Fluorite (X10)
No idea what this is, maybe more fluorite, though I don't see the right habit for that (X30)

Acicular Bertrandite crystals on matrix?  As good a guess as any I suppose (X30)

Calcite on this rock with bands of other mineralize zones, cleavelandite was also observed on this rock



Unknown pink mineralization (center left)
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