What is the common name for a soft dull greenish brown or grey variety of clay that falls to a powder in water?

Option D

Fuller's earth is any clay material that has the capability to decolorize oil or other liquids without the use of harsh chemical treatment. Fuller's earth typically consists of palygorskite or bentonite.

Modern uses of fuller's earth include as absorbents for oil, grease, and animal waste (cat litter) and as a carrier for pesticides and fertilizers. Minor uses include filtering, clarifying, and decolorizing; active and inactive ingredient in beauty products; and as a filler in paint, plaster, adhesives, and pharmaceuticals.It also has a number of uses in the film industry and on stage.

 In past centuries, fullers kneaded fuller's earth and water into woollen cloth to absorb lanolin, oils, and other greasy impurities as part of the cloth finishing process.

Fuller's earth is also known by the following other names:

Bleaching clay, "Whitening clay, Multani mitti