FOSSIL-MEAL, otherwise called hac lunc, mineral argaric,
argaric, and guhr, is, according to M. Fabbioni, a mixed earth, which exhales an argillaceous odour, and throws out a light whitish smoke when sprinkled with water. It is abundant in Tuscany, where it is employed for cleaning plate. It does not effervesce with acids; is infusible in the fire, in which it loses an eighth part of its weight, though it becomes scarcely diminished in bulk; and, according to the analysis made by M. Fabbioni, consists of the following component parts: siliceous earth 55, magnesia 15, water 14, argil 12, lime 3, iron 1. With this earth, which is found near Casteldelplano in the territories of Siena, M. Fabbioni composed bricks, which, either baked or unbaked, floated in water. Hence he infers, that the floating bricks, which Pliny mentions as peculiar to Massilia and Calento, two cities in Spain, must have been made of fossil meal. Bricks made of that substance resist water exceedingly well, and unite perfectly with lime; they are subject to no alteration either by heat or cold; and about a twentieth part of argil may be added with advantage to their composition, without depriving them of the property of floating. M. Fabbioni tried their resistance, and found it very little inferior to that of common bricks; but it is much greater in proportion to their lightness. One of these bricks, seven inches in length, four and a half in breadth, and one inch eight lines in thickness, weighed only 14½ ounces; whereas a common brick weighed 5 pounds 6¼ ounces.
Bricks of fossil-meal may be of important benefit in the construction of reverberating furnaces; as they are such bad conductors of heat, that a person may bring one half of them to a red heat, while the other is held in the hand. They may be employed also for buildings that require to be light; for constructing cooking places on board ships; and also floating batteries, the parapets of which, if made of these bricks, would be proof against red hot bullets; and, lastly, for constructing powder magazines.