Loose Gemstones | Gem Art | Gem Stone Information



	160	DE NATURA FOSSILIUM

	rough stones together. If such lime is used in a wall it will not stand, especially when it carries a heavy load. If the sand contains congealed juices they will exude from the wall and dissolve the plaster. Bitumen is the only impurity that will make the mortar stronger and the structure firmer. The presence of a congealed juice can be detected readily by taste. If sand contains earth it is too harsh and when rubbed between the hands it does not make a creaking noise. Earthy sand will stain a white cloth passed through it. Some sands are dry and these are the most useful in buildings. They are usually sedimentary while fluvial and marine are usually moist and not as useful. Each sand is difficult to dry. When perfectly dry they will neither stand with a vertical wall nor arch as Vitruvius has observed. Sedimentary sands are usually unctuous, fluvial and marine, meager. Sedimentary sand should not be used in plaster because of its unctuous-ness, marine, because of its saltiness. Both will produce cracks in the plaster. The sedimentary is the more useful of the two since it will harden without cracking if some binder is placed in the plaster and also because it does not contain salt. Pliny writers that the sand from many parts of Africa resembles a lentil and that from near the pyramids, Egypt, has both the form and size of a lentil. Also, on a certain long hill of Cappadocia located in a field, the pebbles resemble a lentil.¹⁴ Sand is used not only as a building material but also in cutting marble as I have already mentioned. Coarse sabulum¹⁶ is also sand. It may be either hard or soft, the former being called male, the latter female. The male is more useful as a road surfacing material. It is spread beneath layers of flint and rock and also between layers of these materials. We call fragments of stone, marble, flint, and tofus that are not large enough to be called rocks glarea. But this is enough concerning sandstone, sand, sabulum, and glarea. I shall now take up another genus of rock. Artificers use this as they use sandstone, namely in columns, blocks, and any other forms that are needed in buildings. The tabular blocks are artificially smoothed and then laid in floors and in courtyards such as one in Hesse. These floors are found both in public buildings and private homes of the wealthy. This rock is also used for roofing tiles. The Romans made no distinction between this rock and sandstone but as soon as an iron tool is applied to it the difference is apparent. This genus is found in a variety of colors as is sandstone, white, red, mottled, i.e., white and red, etc. The white is found in Chemnitz in two quarries in the forest on the eastern side, the red and mottled in two quarries near a town on the western side, one in an oblong moun- ^II This is probably a reference to "dreikanters," lenticular stones facetted by the wind. ¹⁶ Sabulum is sand in the sense of a species of earth as contrasted to arena, sand as the barren material of deserts.