chert: variety of silica containing microcrystalline quartz
silica: a white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earth's crust as quartz or cristobalite or tridymite or lechatelierite
nicad: a rechargeable battery with a nickel cathode and a cadmium anode; often used in emergency systems because of its low discharge rate when not in use