Welcome to the final stop
in Doc's Roadside Geology Tour: Jackson County!
The above listed coordinates will bring you to an
extremely rare occurrence in the Midwest. Within this special road
cut, you will be viewing the heart of the “Driftless
Zone.”
The purpose of this EarthCache is to allow you the opportunity
to get up close and personal with the geology at this site, and
compare your findings to the sandstone you experienced at the
EarthCache “Liesegang Bands”.
First, take note of the unusual colours at this ancient
exposure. Take some time to examine the texture and integrity of
the sandstone wall. Feel and observe the hardness of the rock wall,
the differences in hardness of the brilliant red sandstone vs. the
lighter or white sandstone. Also note the size and texture of the
sand granules, both in the wall of the roadcut and the eroded sand
on the ground. The cohesive “cementing material”
creating the rock (or stone) is much more fragile with it's
increased exposure to the elements. Please note the LACK of
protective “oxidative crust” on this stone in many
areas. Also note the changes in the coloration of the red stone
wall. As you move further to your right, you will notice areas
where the color has “washed out” illustrating the
increased porosity in particular areas of this formation.
Sandstone is a sedimentary rock formed over millions and
millions of years. This substrate is commonly composed of quartz
sand grains cemented together by silica, calcite, iron oxide, or
other mineral substance, Depending upon the amount and character of
the cementing agent, sandstones may be almost any color. In this
region of Jackson County, the colors generally range from almost
pure white through shades of yellow, orange, red and brown.
All sandstone is not created equal. Each layer of sandstone is a
unique record of what was was happening atmospherically and
dynamically.
Finer grit sandstone accumulated at greater depths in calmer
ocean waters. The great pressure and introduction of additional
minerals, such as various forms of iron oxide, hematite, limonite,
goethite, etc. contribute to the resultant properties, including
“hardness” and colour, of the final product. When sand
is deeply buried, the pressure of burial and slightly higher
temperatures allow minerals to dissolve or deform and become
mobile. The grains become more tightly knit together, and the
sediments are squeezed into a smaller volume. This is the time when
cementing material moves into the sediment, carried there by fluids
charged with dissolved minerals. Oxidizing conditions lead to red
colors from iron oxides, while reducing conditions lead to darker
and grayer colors.
Conversely, coarser grit sandstone is the resultant accumulation
of quartz granules and additional minerals in a shallower,
generally more turbulent body of water. The pressure exerted is
less due to the depth of water at the time, and increased water
flow will affect the volume of mineral deposition.
The blood red pigmentation you are observing in this roadcut is
due to the presence of a mineral ~ an iron oxide known as hematite.
It is also spelled as hæmatite, and is the mineral form of
iron(III) oxide (Fe2O3), one of several iron oxides. Different
amounts of water saturation will cause precipitation of hematite
vs. limonite and goethite, one rather than another, and they each
have different properties. The abundant iron here may relate to
primary pyrite or marcasite (iron sulfide) in the sandstones which
has oxidized once these beds were exposed by a declining water
table.
The name hematite is derived from the Greek word for blood a?µa
aima because hematite can be red, as in rouge, a powdered form of
hematite. The color of hematite lends it well in use as a pigment,
particularly as an ochre. Ochre is a clay that is colored by
varying amounts of hematite, varying between 20% and 70%. Red ochre
contains unhydrated hematite, whereas yellow ochre contains
hydrated hematite (Fe2O3 • H2O).
You have already experienced one of the properties documenting
the presence of the hydrated hematite (limonite and goethite) as
the golden yellow sandstone at the site of the Liesegang Bands EC,
where the mineral's golden yellow color rubbed off onto the skin of
your hand, indicating it's solubility in oil.
To log this EarthCache, please forward in an e-mail to me, the
following:
1.Is the grit of the sandstone here finer or coarser than the
golden coloured sandstone at the Liesegang Bands EarthCache?
2.What colours of sand do you see here?
3.Does the colour rub off onto your hands?
4.Do you see any Liesegang Banding here?
5.Please take a small sample of an intact piece of red
sandstone, place it in a container and add several tablespoons of
water to the container.
a. Please tell me how long it took for the stone to absorb the
water;
b. Wait 2 minutes, then touch the stone sample. Does it hold
it's shape?
c. Stir the sample and tell me what color the water is after 1
minute of stirring;
AND,
**Please post a photo documenting your experiences at this
remarkable site.**
Thank you so much for joining me on this edition of Doc.'s
Roadside Geology Tour of Jackson County!
I hope you had as much fun discovering these hidden geological
gems as I did.
Hope to see you on the next edition of Doc.'s Roadside Geology
Tour!