Diatomaceous Earth packaged under our Fossil Shell Flour® label comes from an extremely pure fresh water deposit of fossilized Aulacoseira diatoms created in the Miocene epoch. Why is this diatom so special? Its shell is made of amorphous silica. Its shape and hardness in the fossilized form are important to how it works. Its hardness keeps it from dissolving in liquid. The diatom’s tubular shape and holes along the diatom's wall allow it to absorb moisture, hence its use as an anti-caking agent. The tubular shape of the diatom gives it more surface area than other shaped diatoms. This means it has a greater absorptive capacity with the holes that open to the center and improved mixing and flow of animal feed. Fossil Shell Flour® does not swell, does not absorb nutrients and poses no long term hazard when used as an anti-caking agent in your animal's feed. Fossil Shell Flour ® consists of 89% (and often more) Silicon Dioxide plus numerous trace minerals. Fossil Shell Flour® is almost pure white when dry and appears light tan when wet. Other diatomaceous earth deposits often contains an excess of a particular mineral such as iron or a high percentage of clay giving it a darker color or a reddish tint.