Introduction

Diatomite, a soft, porous, fine-grained, lightweight, siliceous sedimentary rock, is produced by the accumulation and compaction of diatom (Class Bacillariophyceae) remains. The cell wall of living diatoms is impregnated with silica (amorphous hydrous, or opaline (SiO2.nH2O)), which preserves ornate and highly porous structures (Armbrust, 2009). Upon death of the organism, these siliceous elements become sedimentary particles in a diatomite deposit. The intricate structure of diatom frustules, and packing of the myriad diatom shapes into rock-forming sedimentary layers, gives diatomite deposits properties that are useful in many industrial and commercial applications. Most diatoms are 10 μm to 100 μm in size, although larger species reach more than 1 mm (Tappan, 1980) and smaller ones are <2 μm. This small size results in large concentrations of diatoms; a cubic inch of diatomite may contain 40 to 70 million diatoms (Crespin, 1946). Although the specific gravity (density) of the SiO2 that comprises the diatom particles is nearly twice that of water, perforations and open structures in the frustule renders diatomite a considerably lower effective density (between 0.12 g cm–3 and 0.25 g cm–3) with high porosity (from 75 to 85 percent). This sedimentary rock is able to absorb and hold up to 3.5 times its own weight in liquid (Cleveland, 1966). These properties bring industrial utility and commercial value to rock-forming accumulations of diatom remains.

Diatomite deposits of varying quality are known from freshwater and marine sedimentary environments (Moyle & Dolley, 2003). Other names for diatomite and diatomaceous earth include tripoli, kieselguhr, and infusorial earth.