Diatomaceous Earth (DE) is not earth or dirt. It is the fossilized remains of microscopic shells created by one-celled aquastic plants (diatoms). Over the eons, as these diatoms fosillized, they retained their tubular shape and holes. Their shape and hardness produces extermely pure and consistent DE.
There are different grade of DE. Of the 600 deposits in the US, only four are considered Food Grade. Food Grade DE is considered GRAS (generally regarded as safe) by the FDA.
Within the Food Grade classification, there is a wide variance depending on whether the DE is from fresh or salt water deposits, and how finely it is sifted.
The best DE is a fine whitish powder that is odorless and tasteless. It consists of 85-92% silicon dioxide and other trace minerals. However, some DE products contain as much as 33% clay, making them less effective.
The silica in Food Grade DE is amorphous. This is silica in its naturally occuring state. It is a trace mineral every mammal on the planet needs for survival. DE is dangerous when the silica in it is crystalized by exposure to extreme heat. This type of DE is never considered Food Grade.