[Rockhounds] BASIC geo-chem question...

[pmodreski at aol.com]

For Dennis,
I'd say the simple answer is, the fluorite was introduced later, after the sediment was deposited and turned to rock, by warm or hot waters percolating through the limestone.  No, conditions would normally never be such for fluorite to precipitate initially in the "ooze of sediment".
In areas with large amounts of fluorite, with mineable deposits, like the Illinois-Kentucky fluorspar district, there were large amounts of fluorine-bearing waters moving into and through the rock formations, probably related to igneous intrusions in the subsurface. Or in other cases, there were subsurface flows of water circulating through thick basins of sedimentary rock, dissolving chemical elements like fluorine and reprecipitating them fluorite in the nearer-surface, cooler rock layers.  Or, the fluorite occurs where there are faults zones, which can carry the fluorine-bearing fluids upward into overlying rock strata.
Fluorite often occurs in limestones in small amounts, even where there are no significant deposits.  For example, around Penn State in Centre County, Pennsylvania, we would often see a few crystals of fluorite in limestone in the local quarries--along with such minerals as calcite, celestite, strontianite.
Pete Modreski
P.S.,--curious, about the Rockhounds list, I saw Alan's response here, but my email never seems to have received the original post of the question.


-----Original Message-----
From: Alan Goldstein <deepskyspy at outlook.com>
To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors <rockhounds at rockhounds.drizzle.com>
Sent: Tue, Jan 28, 2020 12:59 pm
Subject: Re: [Rockhounds] BASIC geo-chem question...

Dennis and anyone else interested:

There is a good publication on fluorine resource in the United States available from the USGS. I used it when researching my article on the IL-KY fluorspar district that was published in the Mineralogical Record in 1997.

https://pubs.er.usgs.gov/publication/pp933

It should answer your questions. 

Alan G.

-----Original Message-----
From: Rockhounds <rockhounds-bounces at rockhounds.drizzle.com> On Behalf Of Dennis Buffenmyer
Sent: Tuesday, January 28, 2020 1:28 PM
To: Rockhound List <rockhounds at rockhounds.drizzle.com>
Subject: [Rockhounds] BASIC geo-chem question...

I live in an area where the rock units are largely sedimentary and specifically, for the most part, limestone. Within the limestone there is  not a LOT of variety of minerals, but often we find Fluorite. I understand that minerals can precipitate and form in the ooze of the sediment by concentration, chemical reactions, salinity, and ph. What I am curious about is, was the fluorite always present in diluted amounts in the limestone, or where did the fluorine originate? Was it present as HF and reacted with the Ca of the limestone?? Just curious if anyone has any knowledge of this. NOT looking for an absolute, but perhaps a predominance of occurrence??


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