diatomite - teaching hand specimen of the Valmonte diatomite , a unit of the Monterey Formation of California
Diatomite or diatomaceous earth is a sedimentary rock composed of the siliceous cage-like shells of diatoms, single-celled algae that live in the shallow water of lakes and the sea. As they die there is a constant rain of their shells onto the seabed and lake bottoms, where they accumulate to form chalk-like diatomite. The shells of diatoms are made of opal, so unlike calcareous chalk, diatomite will not effervesce with a drop of hydrochloric acid.
Diatoms extract the silica of their shells from the water they live in. It takes special conditions to form a deposit of pure diatomite - active volcanism makes silica available, while very cold water inhibits the growth of foraminifera, the plankton with shells composed of calcium carbonate. Diatomite forms in high elevation lakes and in polar seas, and is found where similar conditions existed in the past.
This marine diatomite is from the Monterey Formation on the Palos Verdes Peninsula in Los Angeles County. It overlies the Altamira Shale, lowest unit of the Monterey. The Monterey Formation is the source rock for much of the oil produced in California, thanks to the diatoms.
Diatomite has industrial uses in filtration, in insulation and cat litter, as a filler in rubber, paint, cosmetics and plastics, as a mechanical insecticide and as a stabilizer in dynamite. It is also used as a polishing agent in toothpaste and as a component of some cement blends.
For prepared diatom slides, we recommend Diatom Shop in Italy. Slides are available in scientific and in artistic formats, which are beautiful preparations. You can also purchase unmounted diatoms if you want to prepare your own slides. Diatom Shop has specimens from all over the world.
The specimens shown here are about 1 1/2" thick.
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