Deposit composed of fossil diatoms (see bacillariophyceae), which is mined for many industrial uses: as a mild abrasive in metal polishes, as a filtering medium (e.g. in sugar refineries), for insulation of boilers and blast furnaces, etc., and under the name ‘kieselguhr’ as a vehicle for explosives. Vast deposits of diatomaceous earth (called ‘diatomite’) are mined at Lompoc, California.