Friday, February 18, 2011

Accretionary Wedge #31 - Geo-Epiphanies

This is not exactly a "new" epiphany, but one that has gradually become a greater interest. Sand. In particular, Heavy Mineral Sands. And the more diversity there is in the composition, the better.

I guess the epiphany is that - though I consider myself to be a field Geologist - it would be so easy to get "lost" in the endeavor of peering through a binocular microscope for hours on end. I actually did this with point-counting of petrographic thin sections, when I was an undergrad. In my youthful vigor, I decided it was necessary to count 500 points per thin section, for about 18 or so thin sections (for my undergrad "thesis"). That "cured" me of a desire for microscope work for a few years. My Master's Thesis was field mapping-oriented, so there were only 4 or 5 thin sections, with only a minimum of point-counting.

Anyway, the junior college at which I teach part-time is gradually building a sand collection. Students and faculty (and our friends) have been repeatedly asked to bring a ziplock bag of sand from a vacation spot. Some sand samples which have been collected (by my friends and relatives) include from Jamaica, Grand Cayman, and the Giza Pyramids.


Being a native of north Georgia, gold panning has long been a hobby of mine, but the heavy mineral concentrates in each pan have usually been discarded after any gold (or platinum in one case) has been picked out and saved. That includes heavy mineral concentrates from places I may never again have time to visit, such as the South Fork of the American River, near Coloma and Placerville, California or Aguirre Springs, Doña Ana County, New Mexico (above photo). Nowadays, I have a bit more respect for heavy minerals. Here is a brief blogpost (primarily for non-geologists, including my students). Though, as the intense study of heavy minerals is a bit esoteric, finding texts and articles (on how to distinguish monazite from zircon, for example) is a bit difficult.

After looking for new and interesting lab assignments for my lab classes, I began to spend more time looking through a binocular microscope at sands in general and heavy mineral sands in particular. Here is an example of an online sand exercise. As for studying local north Georgia heavy mineral sand samples, it becomes easier to keep the students' attention, if you tell them that there might be gold in their particular sample. I also tell them that small diamonds have been found in several Georgia heavy-mineral concentrates.


The above-linked online exercise led me to seek, not only creek and river sand samples, but beach sand samples, too. In contrast to the beach sands of the Georgia barrier islands - which are usually 99%+ quartz, the sands of the New York City-area are a fascinating mix. The "urban beach" photo above is from near the Portside Towers in Jersey City, NJ (near where my daughter and her family live). Between the chunks of old bricks, concrete, coal fragments, and other materials dumped for erosion control, you can see the distinctive dark color to the sand that hints at an interesting mix of heavy minerals.

Though I haven't studied these sands in detail, the literature suggests they are largely magnetite and garnet. One of my goals is to visit Montauk Point on Long Island and Sandy Hook, NJ to collect some sand samples from those two areas. And I would also like to revisit the area near Auraria, Georgia where I found a grain of platinum (along with the gold) in my pan, so many years ago.

Yeah, with a good supply of heavy-mineral samples, I could stand to be "chained" to a microscope for a little while. So, "Here's sand in your eye."

4 comments:

  1. Thanks for sharing your insights.
    If you ever want a sample of Lake Erie sand, my mom has a place on that lake. I have always found the sand interesting to look at. It is filled with glacier debris and a lot of man made stuff. You never know what you may find in it. My nieces and nephews have liked collecting the green glass they find in it. If you are interested you can contact me via my blog http://annsmusingsongeologyotherthings.blogspot.com/2011/02/accretionary-wedge-31-what-geological.html

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  2. Ann, thanks. I will probably do that in a few days.

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  3. Thanks for a great post. I have always had an affinity for sand as well. Although we likely don't have much in the way of heavy minerals, if you want some sand from the Great Salt Lake I could send you some. I also hope to have the AW compiled shortly.

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  4. Jazinator, thanks. I will let you know about the Great Salt Lake sand.

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