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Studying Sedimentary Sandstone Banding

Contributions to the Geology of Wabasha County, Minnesota
If you are new to the subject of geology in southeast Minnesota, this reference about geology in Wabasha County is a good starting point. I suggest you scan the articles. Feel free to ask questions about topics you might study.
Age of Dinosaurs in Iowa
The Iowa Geological Survey maintains a series of attractive, informative web pages. You may learn how dedicated members of the public and professional geologists are to the search for Cretaceous Era life forms.

One Cretaceous Boulder in Our Yard

One corner of the boulder exhibits banding. Like any know-it-all, I have walked by the boulder thinking: "the brown layers of sand grains must have been deposited when stream or beach flow was agitated, and the light colored sand must have been deposited in quieter times. Particles in brown layers must be relatively large, then grade upward into smaller clear particles."

I used an Intel Create and Share Camera, plugged into a PCI card mounted in an Aptiva Windows 95 pc, to take the first two photos. It was a clear sunny day.

The pc has a CRT monitor. The usual procedure is to obtain a steady, focussed image in the viewing area associated with the camera software, then direct a mouse pointer at a snapshop button seen on the monitor, and click the left mouse button when ready. I held the camera in my left hand, the mouse in the right. Under the outdoor lighting condition, I could only see the target indistinctly and could at best guess when it was in focus.
Okay, my walking by inferences were wrong. I was seeing banding but not graded bedding.

I examined the banding using a 10X handlens. The sandstone is coarse grained in the region studied. If you are a devotee of Frederic Lahee's book "Field Geology" you can read that when particle sizes range roughly from 0.5 to 2.0 mm, the term coarse grained is applied. I have a copy of the 4th Edition, 1941. Used copies are available on the web. I think it is only fair play to purchase a copy if you are serious about longterm study of geology.

I took my ThinkPad LCD laptop outdoors, plugged my Intel Play QX3+ Microscope into a USB port and used it at 10X while holding it in my left hand. Even when I placed the laptop completely in the shade of the boulder, I could not interpret images on the monitor. I plugged a CRT monitor into the video port of the laptop in order to obtain images nov2301 and nov2303 that you have been seeing. The first of the two 10X microscope images was centered on a brown band. The second of the two was centered between bands. It is image nov2303.

Credit for discovery of the following results must be attributed to Inetis Company. Their unselfish release of Inetis DotColor 3 made it both possible and enjoyable to acomplish them.

I used my Intel Create and Share PCI Camera to give you impressions of what I was doing with 10X microscope image nov2303 on a CRT monitor. I wanted to show you want I meant by brown colored grains. My first guess is that they are limonitic. Images nov2601 and 2602 show results. In image 2602 you see that I was pointing the DotColor 3 icon at a rounded silica grain that has a definite bluish tinge. To me, the apparently relatively large amount of blue in the silica grains is remarkable. I must re-examine the banding after the current snowfall melts (it is now Nov. 28/04). I have not seen a similar phenomenon when examining sandstones with a handlens. Yet I am sure that PCI camera and handlens color perceptions do not differ.

[Dec. 17/04: The blue color seen on Nov. 28 was reflection from overhead blue sky. When observed with overhead grey skies, the silica sand grains had usual clear colors without blue shades.]

The colored panels below the images have RGB values measured for the "brown" and "blue" grains. I asked my wife to identify the color of the left panel. She said: "beige, with a pinkish tinge". I could not have done that. I believe that many of us can perceive color differences, but have difficulty in verbalizing them.

I used DotColor 3 to examine the panels. They have exactly the RGB values I gave them in a Table td tag.

Would I get the same digital mineral color identifications if I used nov2302 image in a laptop with LCD monitor. The images nov2601a and nov2602a below the colored panels give the answer. YES

our address: glennbowie@hotmail.com.