I have been out fishing
and hunting agates again back in the Midwest, at one time my home for several
years. As an avid fisherman I am always searching for the elusive
Northern Pike and Walleye. As a geologist I always have my eyes turned
down looking for agates in shoreline gravels! I am not the only one with this
dual passion as I ran on to a website (www.hotspots.com)
with combination stories of fishing and agate hunting. My kind of
place! I am probably better at catching fish that finding Lake Superior
Agates (Lakers)! However, during this recent trip I was able to procure a
couple of agates from Wisconsin, not an easy task (at least for me).
As I understand the
situation, Lakers have a fairly widespread distribution with the “type” hunting
areas in shoreline gravels of Lake Superior and adjacent sand/gravel
pits. But the Laker name comes, not from Lake Superior, but from the Lake
Superior Till, a covering of glacial debris.
However, glacial
action (Pleistocene) moved specimens into adjacent Wisconsin, Michigan, Iowa,
Missouri, Nebraska, and South Dakota and there are reports of a Laker or two
from Kansas. In addition, Pabian and others (2006) noted Lake Superior-type agates
have been found in deposits of the Mississippi River as far south as
Louisiana. Essentially any “gravel pit” in the glaciated region, or along
the Mississippi River, has the possibility of producing a Laker.
My interest in Lakers
dates “way back” to the 1970’s when I taught a combination canoeing/geology
field course in Minnesota (my idea of a perfect class). Traveling from
western Kansas the class visited many interesting geological localities
including some of the iron mines and taconite concentrators in northern Minnesota.
The “high point” of the class was the week we spent taking a close look at the
old Precambrian rocks exposed in the Boundary Waters Canoe Area. And did
I mention sunsets, bears, campfires, and smallmouth bass? At any rate, on
the way back to Kansas we stopped and searched for agates along the north shore
of Lake Superior. And, we usually had some success.
The original source of the
Lakers is from the basalts (several different layers) 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). The Rift is nearly
1400 miles long extending from northeast Kansas to Lake Superior with an
eastern arm curving around and heading toward Ohio. Hugh amounts of lava
erupted along faults while adjacent rivers from the uplands dumped thousands of
feet of sediments (later sedimentary sandstones and conglomerates) into the low
lands of the Rift. For some reason the rift “stopped splitting” (a failed
rift in geological jargon) and the continent healed. Most of the rocks in
the rift are buried below the surface of the earth and are only known from
geophysical studies and drill holes. For example, the Midcontinent
Geophysical Anomaly (MGA) in Kansas delineates the rift since the concentration
of magnetite in the Rift rocks creates a magnetic “high” that is picked up by
geophysical instrumentation. However, rocks of the Rift become exposed
around Lake Superior and the amygdaloidal 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.
The Wisconsin agates came
from a gravel pit in Trempealeau County, a few miles north of my “headquarters”
in La Crosse. They are not large but do have that distinctive Laker
Look to them. Eckert (2000) notes that all of the Wisconsin counties
along the river have produced Lakers from sand and gravel quarries—and
elsewhere. I visited with an “ole timer” in La Crosse who found a Laker
in a local gravel parking lot. It pays to keep your eyes on the ground,
except when crossing a busy street.
This find prodded me into
checking up on the official State Gemstone of Minnesota and found the following
proclamation: Be it enacted by the Legislature of the State of Minnesota:
The Lake Superior agate is adopted as the official gemstone of the State of
Minnesota. Approved May 15. 1969.
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A pair of Wisconsin Lakers, both ~2 cm.
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I then got to
thinking about other state symbols and wondering about official rocks,
minerals, etc. It was only then I realized that not only did several
states have some sort of an official gem, several states adopted a variety of
agate as their official rock, stone, gemstone, or mineral. In fact,
agates are the most common mineral of the many state symbols. Consider the
following:
Florida Stone: Agatized
Coral is so designated. Of course calling it a “stone” gets out of the
“what is it” debate: mineral or rock. They could have made it the State
Gem except that slot is occupied by moonstone. Yes, Florida has also
given us a State Beverage (orange juice).
Kentucky Rock: the
official State Rock is the Kentucky Agate but of course agate is really a
mineral. However, the official mineral of Kentucky is occupied by Coal, a
sedimentary rock. I think the “symbol namers” were partaking at the
official State Bourbon Festival (Kentucky Bourbon Festival, Inc.).
Louisiana Gemstone: Agate,
which is interesting in that the specimens are alluvial and found in gravels
and are non-native. Are these really Lake Superior Agates transported via
the Mississippi River from Minnesota? Maybe Louisianans had tired of
drinking their State Drink (milk) and skipped over to Kentucky for some adult
refreshments.
Minnesota Gemstone: Lake
Superior Agate. I am particularly partial to the Minnesota State Muffin
(blueberry).
Montana Gemstone: Montana
is the only state with two official gemstones—sapphire and agate. The agates
are multisource specimens so just about any ole agate from Montana will
do. I actually thought their official motto was “Big Sky Country”.
Nope, The Treasure State.
Nebraska Gemstone: Blue
Agate (more of a blue chalcedony) formed in fault and joint planes in wind
deposited siltstones and claystones of the Tertiary age Chadron Formation
(24-37 my) ---the formation common in the badlands of Nebraska and South
Dakota.
Nebraska Rock:
Prairie Agate. Here we go again—calling a mineral a rock. I am
really uncertain about this one as the official state website notes:
“Agate is variegated quartz noted for its layered varieties. In most specimens,
the bands are coarse and differ in color and translucency, as well as in
compactness and porosity. The prairie agate, distinguished from most other
agates because it seldom has these bands.” If it does not exhibit bands
then why call it an agate?
Oregon Rock: Thunder
eggs, known to all collectors far and wide.
South Dakota Gemstone: the
well known Fairburn Agate collected on the plains surrounding the Black Hills.
These alluvial agates are the same as Tepee Canyon Agates collected from
the Minnelusa Formation in situ. Fairburns are among the
more expensive of the agates but are among the more beautiful.
Tennessee Rock: the state
has two official rocks, Paint Rock Agate and limestone. Of course, they
need to change agate to the state gem except that slot is occupied by Tennessee
River Pearls.
So there you have, agates
are the official “something” of nine states. In my opinion, Rhode Island wins the prize for “Least
Unrecognized Official State Mineral’ which is Bowenite (a variety of serpentine).
Now does anyone recognize that name? However, they make up for it by
having a great piece of barbeque meat as their State Bird, the Rhode Island
Red! Second place goes to Massachusetts with another rather unfamiliar
mineral, Babingtonite (calcium iron manganese silicate). The award for
“Lack of Creativity in Selecting a State, Mineral, Rock or Gemstone” goes to
Nevada and its State Rock---Sandstone. Not a specific rock, like Yule
Marble or Salem Limestone, but plain old sandstone. I found this out on
the website of Nevada’s First Lady where she also a hot link to:
“Nevada’s Early BIGFOOT Sightings.” It is also sad to report that my home
state of Kansas evidently does not believe in symbols of a geological
nature. I need to get those school kids working!
REFERENCES
CITED
Eckert, A. W., 2000, Earth Treasures Volume 1: The
Northeastern Quadrant; iUniverse Incorporated.
Pabian, R., B. Jackson, P. Tandy, J. Cromartie,
2006, Agates: Treasures of the Earth:
Firefly Books, Limited.