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Know your Nitty Gritty
Nine out of every ten grains of sand in our Great Lakes dunes are made of the mineral quartz.
Ever notice how our dune sand squeaks under your feet when you walk near the water? Similar to the effect of a finger rubbed round the rim of a crystal goblet, friction is at work here. The weight of your foot creates a friction between the sand's fine quartz crystals and moisture within the sand.
While walking the beach, you might notice thin, shadowy black lines in the white-gold sand. That's not dirt or residue from an oil spill—it's magnetite, a mineral that's smaller and lighter than silica, so it collects on the surface. True to its name, if you run a magnet over magnetite, the black granules will stick to the magnet.
Size It Up
Though Great Lakes dune sand feels fine as silk, only 15 percent of the granules on our dunes and beaches are considered fine—measuring less than 1/4 millimeter in diameter. About 80 percent is made up of granules between 1/4 and 1/2 millimeter. Very few exceed 1 millimeter.
Motion of an Ocean of Sand
A gentle breeze—think 10 mph or less—is all it takes to get fine sand airborne. Bigger grains, those up to 1 millimeter, need a 20 mph boost, but they'll generally move along the ground. Give them a gale of 40 mph or more, and they'll not only catch air and bounce along the surface (a motion called saltation), their impact will kick the heaviest grains along too (a motion called impact creep).
Lynda Twardowski is travel editor at Traverse, Northern Michigan's Magazine.
Note: This article was first published in July 2007, and was updated for the web February 2008.