OBJECT OF THE MONTH - FEBRUARY 2010
Diatomaceous Earth: From tooth powder to predicting the future
Diatomaceous earth (or diatomite)is those sediments that are 90% or more composed of the cell walls of diatoms. Diatomites can be of marine, estuarine or freshwater origin, and are found in the U.S., primarily in California (where the world's largest producer of diatomaceous earth is located in Lompoc), along the West Coast, in inland areas such as Nevada and Nebraska, and in the northeastern states. Check out Vivian Diatomite Operation to see what diatomite looks like in the field, and learn about its impact on a local community. In Colorado, small amounts of fiatomite can be found in the Great Sand Dunes area. Large quantities of diatomite occur around the world. China, Russia, Iceland, and parts of the Middle East have large deposits, in addition to those found in the U.S.
When diatoms die, their glass cell walls sink to the bottom and become incorporated into the sediments. There they can accumulate over time and become a record of past environmental conditions, since different species occur within a narrow spectrum of factors. When huge populations of diatoms "bloom," their cell walls build up to comprise the vast majority of sediments, and over time they cancreate deposits we now call diatomaceous earth. It has been estimated that within a cubic centimeter of diatomite, nearly 1 billion cells can be found. The deposits in Lompoc cover many square kilometers and hundreds of meters in depth—the enormous number of diatoms making up those deposits is staggering.
Under the pressure of building up of millions of years of sediment, the diatom cell walls fracture. Their fine pores and the broken glass nature of the diatomite, yield interesting properties of diatomite. Organic gardeners use diatomaceous earth as a deterrent for pests (insects and slugs don't want to cross the glass shards circling vegetable plants), and the material is a wonderful abrasive. It does such a good job that it is included in brass and silver polishes, and it used to be incorporated into tooth powder. However, it is so good an abrasive that it will take the enamel off of your teeth—and therefore it is not found in today's toothpastes.
Diatoms make excellent filters, and many white wines, beers, and other products are filtered through diatomaceous filters. Many swimming pools have diatomaceous earth filtration systems. The fractured cell walls also provide great conducting properties, and diatomite may be used in insulation and similar applications.
The United States Geological Survey has data on the use and sale of diatomite as a commodity, and locations across the U.S. at U.S. Minerals Information: Diatomite.
Beyond the practical nature of diatomite, the record of past environments they have captured may give us a clue about the future. Past warming events in the earth's history happened at times when diatomite formation occurred. Thus, looking at the number and types of species in diatomites can give us clues about what scenarios for the production of organic compounds from atmospheric or aquatic carbon dioxide might look like, and the implications of those scenarios for everything from food webs to carbon dioxide cycling. The beautiful cell walls of diatoms have many interesting stories to tell.
