URL: Identify a Rock
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Complete with photos and information about each rock’s distinguishing characteristics.
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Idea: Gather rocks and fire them. Unexpected results!
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I gathered these downstream from the Oldman River dam in southern Alberta, not far from where the river exits the Rocky Mountains (it cuts through many different rock strata upstream, including both limestone and dolostone, as well as quartz sandstone and siltstone). Upper left: The gravel bar where I collected them. Upper right: The rocks as gathered. Lower left: After firing to cone 04 (about 1900°F). Lower right: After I poured water on them!
Seven disintegrated before my eyes—with sound effects, intense heat and even steam! That identifies them as carbonate-rich rocks, likely limestone or dolostone. Firing drove off their CO2 and caused considerable weight loss, converting the calcium carbonate to calcium oxide—quicklime. Dolostone also produces magnesium oxide. When water was added, the CaO rapidly hydrated to calcium hydroxide, releasing enough heat to break the rocks apart. Two others cracked badly just from the firing. The survivors appear to be more silicate-rich siltstones and sandstones—and some of them can withstand considerably higher temperatures.
The exciting part of this: A river gravel bar is really a randomly assembled collection of ceramic raw materials. Next project is to fire more rocks to cone 6 and 10.
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