(argillaceous), a genus of argillaceous earths. Its texture is more or less porous, equable, and rough to the touch. It does not give fire with steel, nor effervescence with acids. When fresh broken and breathed upon, it exhales an earthy smell. Mr Kirwan mentions two kinds; one from Hollington near Uttoxeter, of a yellowish or whitish grey, and about the specific gravity of 2.288. Another, from Kneepersley in Staffordshire, is of the specific gravity of 2.568; and so unfusible as to be used for fire stones. According to Fabroni the grit-stone is of greater or less hardness, mostly of a grey, and sometimes of a yellowish colour, composed of a siliceous and micaceous sand, but rarely of a sparry kind; with greater or smaller particles closely compacted by an argillaceous cement. It gives some sparks with steel, is indissoluble for the most part in acids, and vitrifiable in a strong fire. It is used for millstones and whetstones; and sometimes for filtering stones and for building.