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| 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.
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| 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.
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| 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.
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| OFTEN FAIRBURN AGATES ARE NOT "CHEAP". |
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| 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