TALC, in natural history, a large class of fossil bodies, composed of broad, flat, and smooth laminae or plates, laid evenly and regularly on one another; easily fissile, according to the size of these plates, but not all so in any other direction; flexible, and elastic; bright, shining, and transparent; not giving fire with steel, nor fermenting with acid menstrua, and sustaining the force of a violent fire without calcining.