VARIETIES OF ORNAMENTAL AND COVERING STONES

Under the commercial point of view, ornamental and covering stones are basically subdivided into granites and marbles. Generically speaking, granites are considered as silicate stones, while the marbles are, lato sensu, the carbonate stones. Some other lithological kinds included as ornamental stones, are the quartzites, serpentinite, travertine, and slates, also very important in this activity sector .

There are two simple procedures recommended to distinguish between a granite (silicate stone) and a marble (carbonate stone), as follows: the granites aren't marked by pocket knives and keys; the marbles, including travertine, are marked by pocketknives and keys and react to the chloride acid attack, with 10% in volume, getting fizzier as the calcite character is higher (in lack of chloride acid, the use of lemon is suggested). Serpentinite and slates don't fizz or fizz very briefly, and can be marked by pocketknives. Neither pocketknives nor fizz with chloride acid or lemon are able to mark the quartzites, although very often associated to the marbles.
Isotropic stones, with no preferential orientation of the mineral components, are designed homogeneous and more used in covering works. Anisotropic stones, with drawings and mineral orientation, are called active and more used in isolated pieces, because its application in coverings request aesthetic refinement and describes a new tendency of design, still not completely assimilated by most traditional consumers.

The chromatic pattern is the main attribute in consideration for commercial qualification of a stone. Due to the chromatic characteristics, the materials are placed as classic, common or exceptional. The classic materials don't suffer the influence of fashion or current style, including red, white, yellow and black marbles, as well as red and black granites. The common or "battle" materials of large use in covering works, include beige and grayish marbles, besides grayish, rosy and brownish granites. The exceptional materials are usually used for isolated pieces and small coverings, including blue, violet and green marbles, in addition to blue, yellow, white and multicoloured granites.
Commercial designations are often exotic and deceiving, not referring to the actual parameters of color and material from the sources. The traditional nomenclature reflect those parameters (e.g.: Green Candeias, Capão Bonito Red, Sardo Pink, etc), and should be adopted as for identification of new commercial type material.

Commercial products obtained from the extraction of blocks and sawing of plates, that suffer some kind of treatment on surfaces (specially shining and polishing), are called special processed stones. This is the case of those materials that generally accept polishing and receive calibration, and this covers marbles, granites, solid quartzites and serpentinites.

Commercial products generally used with natural surfaces in non-calibrated pieces, directly extracted by mechanical delamination of plates in the quarry, are designed as simple processed stones. For illustration, it is known that in Brazil that is the case for the foliated quartzites (like São Tomé stone, ‘mineira’ stone, ‘goiana’ stone etc.), besides Cariri stone, ‘gaucho’ basalt, Miracema stone, Macapá stone, Morisca stone, among others, Cairi stone being the only one from "carbonate origin".
The slates receive specific appellation, the commercial names being distinguished according to the color of the stone. Commercial products from the serpentinites are named “green marbles”.