marble in egypt: marble uses

Marbles are used principally for buildings and monuments, interior decoration, statuary, table tops, and novelties. Colour and appearance are their most important qualities. Resistance to abrasion, which is a function of cohesion between grains as well as the hardness of the component minerals, is important for floor and stair treads. The ability to transmit light is important for statuary marbles, which achieves its lustre from light penetrating from about 12.7 to 38 millimetres (0.5 to 1.5 inches) from where it is reflected at the surfaces of deeper lying crystals. Brecciated, coloured marble, onyx marbles, and verd antique are used principally for interior decoration and for novelties. Statuary marble, the most valuable variety, must be pure white and of uniform grain size. For endurance in exterior use, marbles should be uniform and nonporous to prevent the entrance of water that might discolour the stone or cause disintegration by freezing. It also should be free from impurities such as pyrite that might lead to staining or weathering. Calcite marbles that are exposed to atmospheric moisture made acid by its contained carbon dioxide, sulfur dioxide, and other gases maintain a relatively smooth surface during weathering; but dolomite limestone may weather with an irregular, sandy surface from which the dolomite crystals stand out.

The main mineral in marble is calcite, and this mineral’s variation in hardness, light transmission, and other properties in divers directions has many practical consequences in preparing some marbles. Calcite crystals are doubly refractive—they transmit light in two directions and more light in one direction; marble slabs prepared for uses in which translucency is significant are therefore cut parallel to that direction. Bending of marble slabs has been attributed to the directional thermal expansion of calcite crystals on heating