RARE Glover Bluff Wisconsin USA IMPACTITE 138-gr. (4.8-oz.), 8.2-cm (3 1/4-in.)

Description

There is, quite understandably, a growing interest in large meteorites and asteroids. That such large objects have struck Earth in the past, and will continue to in future, is something scientists have only fully begun to appreciate since about 1980. At present, there are over 170 recognized impact structures, and, every year, one or two new ones are being confirmed. Perhaps one hundred potential sites awaiting study. Confirmation of new impact craters takes a lot of time because there are probably more workers at the average McDonald's Restaurant than geologists who study impact craters!
The impact creates a crater far larger than the size of the impacting body.
Small craters resemble simple bowls; larger
ones may contain a central uplift or peak and multiple rings.
Local or area rock and soil are vaporized. Fallback material
may fall into or around the fresh crater, or be bourne many km (miles) away. Melted
fragments may be tossed at high
speed becoming aerodynamically-sculpted as impact melt glass bombs. Or
soil and sand may quickly cool into impact
melt glass. LONG after erosion has eraised signs of craters, such
impactites
may remain.
Offered here for your kind consideration is a very fine impactite, a one-cm (~3/8-inch) thick slice of layered resurge sand breccia from
the Glover Bluff, Wisconsin, USA impact crater.
The quarry was active for years, and I understand it is now closed, so such specimens
are rarely available. I cut this
unpolished slice of hard impact breccia from an otherwise unremarkable rough flattened chunk.
It is
roughly 8.2 x 4.0 x 2.0-cm (about 3 1/4 x 1 9/16 x 3/4-inches) and it weighs 138-grams
(4.8-oz.).
I will include a
roughly 5.0-cm (2-inch) wide descriptive label printed on cardstock
(not shown)
that
identifies the
specimen, the crater size and age,
and states this is
from the collection of Richard Dreiser
.
The photographs were taken with the slice
wet with tap water
to accentuate the contrast and color. You can achieve the enhanced color and contrast either by polishing it if you have the wherewithal, or,coating it with a thin layer of clear polyurethane (sprayed, or brushed on).
The Glover Bluff meteorite crater is located about 6.4-km (4-miles) south of Coloma, Wisconsin in the midwestern United States,
close to 153-km (95 miles) from where I live. The crater is roughly 8-kilometers (5.0-miles) in diameter and the age is estimated
to be less than 500 million years (making it from the Cambrian or younger). The crater is exposed at the surface. So far as I know,
the Glover Bluff Quarry is now closed to collectors.The site is among the least studied in the world, in part because the uplifted
central area has for decades been actively quarried for dolomite beneath the moraine left by retreating glaciers. Ironically, the
very evidence supporting a meteoritic impact origin uncovered in the quarrying process was systematically destroying the crater.
Such evidence includes a central bulge, dipped strata, the presence of "shatter cones" (although likely these were no longer as
common as they may once have been), and, "impact breccia." There are red, yellow, and tan varieties, sometimes found in a quite
colorful apparently melted mixture.
The yellow is ancient sandstone. My general impression is that the red variety lies directly atop the ancient sandstone.
The layering show the astonishing effects of resurge sand sloshing back into the crater. At least that is my impression.
The breccias contain many broken fragments (or shards) of quartzite and other rocks, including breccia in breccia.
I would love to keep this specimen, however, after sixty years of collecting, I'm retired, and I must be getting rid of some of my most
cherished specimens. I can ship this via First Class Mail within the USA. I can also combine other winnings and ship in the same
carton to save you postage.
IMPACTITES may be mixtures of local shattered and melted local or area rock and dust deposited many kilometers or miles away.
These mixtures may harden into new rock types called impact breccia or fallback breccia. Monomict breccia has only one variety
of rock fragments while polymict breccia has two or more varieties of rock, sometimes with melted glass.
The pressure of impact from a comet or asteroid is far greater than the force of an earthquake, tsunami or super-volcano. It can
affect a number of local or area Earth rocks, sand and soil, sometimes profoundly so. Long after a meteorite impact crater has
disappeared from the landscape, buried or eroded away these, "impactites," may yet remain.The impact creates a crater far larger
than the size of the impacting body. Local and area rock and soil are vaporized. Small craters resemble simple bowls; larger ones
may contain a central uplift or peak and multiple rings. Melted fragments may be tossed at high speed becoming aerodynamically-
sculpted as impact melt glass bombs. Or the soil and sand may quickly cool into impact melt glass.