Cretaceous Clay EarthCache
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This earthcache is located in Alexander Ramsey Park, Minnesota’s largest municipal park. Park near the shelter built by the WPA . While in the park, visit the zoo and the numerous traditional caches hidden in the park.
Across the Redwood River from this site are high banks of whitish clay. This clay is the weathering product of Morton Gneiss (pronounced “nice”). Morton Gneiss, a type of granite, can be observed seven miles downriver from this site along highway 19 near Morton. This can be seen at the earthcache Rainbow Gneiss. This gneiss was formed by high temperatures and pressure deep within the earth’s crust. Geologists have determined that this clay could only have formed in a tropical climate where the minerals within the gneiss decomposed into clay under warm moist environmental conditions. This climate was present in Minnesota during the Cretaceous period, some 100 million years ago. When the Morton gneiss was exposed to air and water, the rock decomposed and became clay. Some minerals in the gneiss granite are more stable than others. The feldspars and micas in the rock incorporated water during their decomposition and formed clay. The quartz, which did not breakup easily, remained within the clay as small pieces of sand. After the formation of this clay, as the Cretaceous seas retreated from the continents, the world’s climatic zones became more pronounced. Minnesota gradually developed its current climate. This cold, relatively dry climate could not further decompose the gneiss. The clay found here is rich in kaolin and is mined in nearby areas of the Minnesota River Valley. Kaolin is used in ceramics, medicine and as a food additive, in toothpaste, as a light diffusing material in white incandescent light bulbs, and in cosmetics. It is generally the main component in porcelain.
Sources Samsome, Constance J. “Minnesota Underfoot - A Field Guide to the State’s Outstanding Geologic Features” 1990, Voyageur Press Ojakanges, Richard W. “Roadside Geology of Minnesota” 2009, Mountain Press Publishing Company Wikipedia: Kaolinite
To claim credit for this cache email the answers to these questions.
1. How tall is the bank of residual clay across the river?
2. What is the commercial name of the Morton Gneiss?
3. The stone on the base of this marker is made from Morton Gneiss. Observe the shiny quartz pieces and email me a list of colors you can see in the gneiss.
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