Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/756888
Bill Langer is a consulting research geologist who spent 41 years with the U.S. Geological Survey before starting his own business. He can be reached at Bill_Langer@hotmail.com CARVED IN STONE 44 AGGREGATES MANAGER / December 2016 B efore I finish this series of columns on geologic curiosities and wonders, I have one more geo- logic curiosity to talk about — your aggregate operation. And even though I probably have not visit- ed your specific quarry or pit, believe me when I say, "There's something curious going on there." There were obvious geologic curiosities in some places I visited, such as the gnarly mastodon teeth found in a gravel pit near Denver, Colo.; the cute kind- chen found in a quarry near Saint Joseph, Mo.; or the beautiful crystals from a stone quarry at Mont Saint- Hilaire, Québec, Canada. But most aggregate operations I have visited are not blessed with such rare curiosities. You might be think- ing, "Yah, that's my boring place." Boring? Humbug. Take, for example, a sand and gravel operation near Cañyon City, Colo. Generally, the top size of the gravel was about 6 to 8 inches. But there were piles of VW-Bug-sized boulders all over the place. Some of those boulders were sold for landscaping applications. Where did those bizarre boulders come from, and how did they get there? The answer may lie in the fact that the operation was in a sand and gravel deposit of glacial origin. How about the beautiful banded rocks in the Helidon Sandstone quarry near Toowoomba, Queensland, Australia? Does the superheated water and gas from ancient volcanic activity have anything to do with why they make such beautiful stone slabs? While studying a gravel pit in Phoenix, Ariz., near my home, I saw curious black splotchy areas (manganese dioxide) where all the cobbles were weak and rotten. Hmmm. Those were areas to avoid when making high-spec aggregate. How curious. I visited a number of limestone quarries near Saint Joseph, Mo. Just below the root zone near the land surface was a tan silty soil (the loess that contained the kindchen). Immediately below that was a strange thin zone of soil containing pink- ish-purple gravel and cobbles. Those stones were collected and sold as premium landscape rock. But where did these curious stone rocks come from? Hint: the area was once covered by a glacier that extended from Canada into Missouri. Along the way, the glacier passed over an area of pinkish-purple quartzite rock near Sioux Falls, S.D. Let's get to a really boring pit — like many I have seen, and maybe even like yours. Nothing special, just monotonous lay- ers of sand and gravel, occasionally interrupted with lenses of clay. The clay causes processing problems, so nobody likes it. Seriously; nobody likes the clay. Well, geologists like the clay. There are a number of reasons why it might be there. One possibility is that the sand and gravel was laid down by an ancient river or stream. Occasionally, the river would overflow its banks and the clay would settle out in quiet backwater areas. Pollen would also settle out in the same area and be preserved in the clay. The science of interpreting pollen is called palynology, from the Greek word meaning "the study of scattered dust." Palynol- ogists can look at the pollen in the clay and tell you what the climate was like at the time and maybe even how long ago the clay was deposited. Now, how cool is that? So never fear; the next time you go to your quarry or pit, just look around. I guarantee there's something curious going on there. No round-up of geologic wonders would be complete without including a look at your very own underappreciated geologic wonder. Your Aggregate Operation Each aggregate operation has a unique aspect to it; be sure not to overlook yours.