Stone and Masonry

The builder of a stone structure is more concerned with its chemical composition than its geological classification. There are three main categories for stone chemical content. Siliceous stone has as its main element, silica, or silicon dioxide (SiO²). Most stone from volcanoes is siliceous. This type of stone also includes compressed sediments of siliceous stone, like sandstone. Quartz is a very pure pressurized sandstone.

Argillaceous stone has as its main element alumina AlO₂). It, along with its compounds, comes from feldspar in the crust. When these meet up with the atmosphere, they change into clay-like compounds. Slate, a sort of petrified clay, is the most common to the mason. When clay combines with other stone in varying degrees, it can overlap into other types. If clay and sand mix, brownstone is formed. Brick is artificial argillaceous stone.

Calcareous stone is made up mostly of calcium carbonate (CaCO₃), or lime. Lime comes from the bodies of sea creatures, whose skeletons have accumulated at the bottom of the seas. When lime is pressurized for millennia, it becomes marble. Marble is mainly a metamorphic rock. But because it is still mainly lime after metamorphosis, it is calcareous in classification.

Certainly, there are many combinations of the above three classifications, but rocks are distinguished by the abundance of glassy (silceous), clayey (argillaceous), or limy (calcareous) material in them. It is the quantity of each basic compound found in rocks, along with the way they were formed and the presence of other minerals in smaller amounts, that give rocks their particular desirability by masons.