Wednesday, August 1, 2012

AGATES AT THE AFMS


THE GYM AT HOPKINS HIGH SCHOOL WITH EXHIBITS AND DEALERS
Agates, agates and agates; more agates than I have seen in my entire life---all spread out on tables and cases at the annual American Federation of Mineralogical Societies annual show and meeting.  This gala event was hosted by the Minnesota Mineral Club and held in Minnetonka, Minnesota (Twin Cities metro area).  The club sponsored a number of formal seminars on agates (paid admission) plus several free presentations concerning the honored gemstone.  Because of previous scheduling conflicts, I was only able to attend the Saturday events but was overwhelmed by the expertise of the presenters, as well as by the sheer numbers of agates displayed in formal exhibits, and “for sale” by the dealers.
DOES THIS SEEM AN OXYMORON?  I THOUGHT ALL GEODES WERE "OLD"!

It was easy to observe that the major emphasis of the show (exhibits and dealers) was on the famous Lake Superior Agates (the Lakers).  That fact is understandable since Minnesota is the major home of most of the discoveries in shoreline gravels of Lake Superior, although later glacial action has moved specimens into adjacent Wisconsin, Michigan and even South Dakota (and perhaps others).  The original source of the agates is the basalt located in the Midcontinent Rift System (MRS).  This geological rift (think about the great East African Rift Zone) begin to form in the Precambrian (Proterozoic Era) perhaps 1.1 Ga splitting the stable part of the North American “continent” or plate (referred to by geologists as the craton).  For some reason the rift “stopped splitting” (a failed rift in geological jargon) and the continent healed.  Most of the rocks in the rift, generally igneous and sedimentary, are buried below the surface of the earth and are only know from geophysical studies and drill holes.  However, the rocks become exposed around Lake Superior and the agates erode from the basalts.  Since the rift rocks include substantial amounts of iron, the agates have some sort of a red or orange color---oxidized iron.  Most likely the agates formed post-deposition of the basalt and are the result of percolating silica-rich groundwater filling the many vugs or vesicles in the basalt.

A MIGHTY LARGE AGATE.
The second most popular agates at the show were the Fairburn Agates from neighboring South Dakota.  I have written about these gems in previous articles but can only restate the obvious---they are spectacular in all aspects.  Generally Fairburns are found on the plains in states surrounding the Black Hills, with most discoveries in South Dakota.  The original source was from the Paleozoic Minnelusa Formation in the Black Hills—generally termed Teepee Canyon Agates at their source.
OFTEN FAIRBURN AGATES ARE NOT "CHEAP".



A BUNCH OF FAIRBURN AGATES.



The meeting and the show were a great success and the Minnesota Mineral Club is to be congratulated for their hard work and dynamic membership.
mike          

4 comments:

  1. The agates in the picture labeled "Often Fairburn Agates are not "cheap" which are priced at $100 each are Lake superior agates, not Fairburn Agates.

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    1. Sorry but they were label as Fairburn by seller and I believe that is correct. They are not Lake Superior. mike

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  2. I think they're lake superior agates as well

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  3. definitively Lakers,,, all 7

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