sand - coarse sand composed of polished chert grains derived from the Franciscan complex - set of two 2-ounce jars The Navajo Sandstone makes up

The Navajo Sandstone makes up the cross-bedded cliffs at Zion National Park in Utah

Untreated chalcopyrite should look brassy

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

but it can be massive vitreous or crystalline and can occur in the form of nodules up to several feet in diameter

When this sand is gone

sand - coarse sand composed of polished chert grains derived from the Franciscan complex - set of two 2-ounce jars The Navajo Sandstone makes upSand 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.