sand - coarse sand composed of polished chert grains derived from the Franciscan complex - set of two 2-ounce jars Sand grains in the Navajo

Sand grains in the Navajo are entirely frosted quartz dune sand

the air and moisture in the sand are rapidly heated

The grains were blown against each other in a huge dune field

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which continues to operate the mine (photo) for lead and zinc

sand - coarse sand composed of polished chert grains derived from the Franciscan complex - set of two 2-ounce jars Sand grains in the NavajoSand is derived from whatever material is available. In this case, the source of the chert pebbles is banded ribbon chert which alternates with thin shale beds of the Franciscan Complex in the Marin Headlands. The Franciscan is a body of rocks scraped off the Pacific Plate as it subducted under the North American Plate. The chert underlies roughly half of the rocks in the Marin Headlands, which support the north end of the Golden Gate Bridge.