sediment types : LUSENET : Introductory Geology, Oswego State : One Thread

I'm having trouble understanding the difference between chemical and biochemical sediments as the book explains them. If biochemical sediment isn't dissolved, what seperates it from clastic materials?

-- Hillary Millman (, April 03, 2001


I do not make a distinction between chemical and biochemical sediments like the book does. Biochemical sediments are ones formed by organisms. For example, a clam extracts calcium and carbonate ions out of seawater and makes its shell out of calcium carbonate mineral. When the clam dies, it sits on the bottom and is then a "biochemical sediment." The book considers a "chemical sediment" to be a mineral that formed by direct precipitation out of water. For example, if you take a teaspoon of sea water and let it sit out and evaporate, you'll find a white "rind" of mineral material on the spoon after the water evaporates. That white stuff is minerals that formed by precipitation from water, and then were deposited on the spoon. That's how "chemical sediments" form, according to your book. I call all sediments that form from materials dissolved in water, whether formed by organisms or direct precipitation, chemical sediments. Does that explain it?

-- Sharon Gabel (, April 03, 2001.

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