Understanding Clay, the smallest piece of rock

Every year the ocean moves the sand on Florida beaches, sometimes into less convenient positions, and every year soil dredgers operate large compressors to blow clean white sand back onto Florida beaches. One man had been swept overboard three times in high waves as his platform with the dredging machinery maneuvered large bays, such as the Chesapeake, or coastal regions of Georgia and Florida. "Clay," he exploded, "is the worst thing for our machine! It stops it right up. But sand is easy; it moves right through. I love sand, not clay!"

When minerals break down (weather), they produce small particles – sand, silt, or, smallest still, clay.

You can see a chart of different sizes here:

http://en.wikipedia.org/wiki/Particle_size

Clay is made up of particles less the 2 micron. or 0.002 mm, which are even smaller than sand and silt. Clay particles can be so small that it could take hundreds of years for them to settle from the top to the bottom of a bottle of water; so small even water and air are obstacles to their movement. Anything they encounter slows them down!

Silt particles, which are larger than clay particles, can be carried by swiftly flowing water to the mouth of a river where they settle. Silt buildup creates islands and blocks the mouths of rivers. The smaller clay particles settle out when the water flow becomes slower yet.

Clay particles are flat and tend to interlock tightly like tiny bricks. They bound together with water. You can easily slide in clay because the attachment of the particles is so strong along planes.

[Picture of Vermont slate and rock]

Shale or slate (the metamorphic form of shale) is clay that has been turned to stone. If you find shale or slate, you can imagine that the area was once a calm, shallow water environment where the particles fell to the bottom…slowly.

Clay comes in many different colors because of the minerals that attach easily to the small particles. Red, yellow, and red-brown colors indicate the presence of iron.

Every year Pueblo potters of New Mexico, USA (above) go to look for the right clay, a clay that fires well, takes a glaze, and is suitable for pot-makers. Each tribe knows where its clay can be found, and the pots of each pueblo reflect the differences in the clays.

If you heat clay in an oven without oxygen it will turn blue-green or black. The black tones of the pottery made by Native American potters of San Ildefonso Pueblo are famous in the United States. When rubbed with a stone, those pots take on a shine. Clay in a body of water that cannot get oxygen, such as a slow-moving estuary, is also black.

Some scientists think life may have begun in clays. Iron in clays could capture nitrogen and carbon dioxide and make citric acid. Amino acids, the building blocks of proteins, can be made from citric acids. IN fact, one iron-rich mineral, when seen in cross-section, looks remarkably like DNA!