[f. FLOAT v. + STONE.]
1. A bricklayer’s rubbing-stone for smoothing the surfaces of bricks used in curved work.
1703. Moxon, Mech. Exerc., 246. Some use a Float Stone, with which they rub the moulding of the Brick.
1812. J. Smith, The Panorama of Science and Art, I. 196. The stone upon which bricks cut with curved surfaces are rubbed, is called a float-stone, which must itself necessarily be curved in the reverse form, though of a radius equal to that intended for the brick.
2. A stone so light as to float upon water, e.g., a spongy variety of opal.
1805. R. Jameson, Min., II. 552. Floatstone … is light yellowish grey.
1814. trans. Klaproth’s Trav., 57. Here is a range of float-stone hills, extending to a considerable distance east and west of the Oka, and containing iron ore, which is wrought in several places.
1859. D. Page, Handbk. Geol. Terms, Float-Stone.… A variety of earthy silica, of a coarse porous aspect, soft and often friable, and of a yellow or greyish-white colour. Being porous, it swims on water till saturated.
