THE ROCKS | Commercial Classification

The world of construction (contractors, builders, project designers, suppliers, ...) uses daily-called trade classifications, whose approach is greatly simplified for easy use. The commercial classification proposed here therefore has no direct link with the scientific classifications developed by geologists and whose most used in Belgium, trade names such as commercial broadcast classifications have often resulted in false names, names being created unrelated to the geological nature or origin of the stone.

Therefore, the commercial classification presented below, prepared in collaboration with the CT 'Stone and Marble' is very close scientific classifications to avoid as much as possible personal confusions. It focuses on the three main families of rocks previously defined and is divided as follows :

      Magmatic rocks :

- Granites

- Basalts

     Sedimentary rocks :

- Sandstone and siliceous rocks

- Carbonate rocks:

- Calcareous sandstone

- Marble limestones

- Limestone non masons

- Slates, shales and schists

     Metamorphic rocks :

- Slates, shales and schists

- Gneiss

- Μarbles.

    This classification is used by the search engine of the natural stone database that provides access to technical data. These include on the name of reference, the trade name and the macroscopic and microscopic description (petrography) stone.

      1 Magmatic rocks :

In this commercial classification, we will call 'granite' all plutonic rocks with large crystals easily discernible to the naked eye (phaneritic texture), and 'basalt' volcanic rocks whose crystals are mostly invisible to the naked eye (aphanitic texture). Compared to the old classifications (NIT 205), granite-term (at large) here is more restricted since it no longer covers the metamorphic rocks.

Granite 

Basalt 

Basalt 

Granite 

       2 Sedimentary Rocks :

The sedimentary rocks are represented by the largest number of categories. These reflect the diversity of training methods and the nature of the material, which inevitably leads dissimilar mechanical characteristics and different applications.

The first category is that of sandstone and siliceous rocks. It mainly consists of the stones used in the building for the paving and paving of roads and exterior for carrying rubble walls. This is essentially the stone rough feel, which tones often vary within the same supply.

Carbonate rocks comprise the vast majority of stones and were divided into three subgroups:

the sandstone or limestone detritus with significant fraction of other minerals as calcite, such as quartz and / or glauconite

the limestone marble workers

calcareous non masons.

The latter two subgroups differ notably during polishing. The distinction is very important from an architectural point of view, because it determines whether the stone takes a good or not polished. Generally, compact rocks, so little porous, give better polished than the so-called soft stones (porous). A marble stone usually has a density greater than 2500 kg / m3. Among non marble stones, we find the majority of French white stones.

Sandstone and siliceous rocks

Carbonate Rocks 1 Limestone sandstone 

Carbonate Rocks 2 Limestone and marble workers marble workers not

Slate, sands and shales

The last category, slates, schists and shales, overlaps sedimentary and metamorphic rocks. It is indeed very difficult for the common man to establish a boundary between the purely sedimentary schist and slate, shale has undergone metamorphism more or less important. In addition, the French vocabulary is less precise and less rich than the Anglo-Saxon lexicon (and Dutch). Table 3 presents briefly the terminology of these rocks in the three languages ​​by associating the diagram of each structure (*).

These rocks belong to the large group of "mudrocks" (literally "mud rock") of English geologists. This group includes all siliciclastic sediments consist mainly of elements of the size of silt (1/16 to 1/256 mm or 0.062 to 0.004 mm) and clay (<1/256 mm or 0,004 mm).

Lundegård and Samuels (1980) designates as the "shales" of compacted clay, more or less rich in silt, with a fissilité parallel to bedding. They note that in Belgium, frequently used in the field the term "slate", which applies to an indurated rock of fine particle size, affected by a foliation, ie d. cleavage due to the simple redirection of minerals under the influence of tectonic pressures (fracture cleavage). According to these authors, the term "slate" or "phyllite" against imply by metamorphism in which most minerals have crystallized and new species appeared. Thus developed minerals are lying in planes perpendicular to the tectonic pressure. Alongside these plans, the rock debits into thin glossy plates, finely crystalline appearance (split flow).

     3 Metamorphic Rocks :

Regarding the commercial classification of metamorphic rocks, it was decided to consider only the most common categories related to two facies minerals opposite texture and macroscopically recognizable: foliated rocks and non foliated rocks.

Foliated: Slate Herbeumont

Not foliated:

marbles

Foliated: Gneiss

The notion of marble used here is clearly related to the origin of the stone, a metamorphic and carbonate rock.

Gneiss is like granites (narrow sense), rock composed of alkali feldspar, quartz and mica. Minerals are arranged in beds overlooking a striped appearance. The overall color is gray, pink, reddish, more rarely greenish. Numerous mineralogical varieties result from the nature of the heavy minerals (muscovite, biotite, amphibole, pyroxene, garnet, etc.). Available minerals and beds determines a nomenclature due to the texture (oeillée, banded, granitoid, etc.).

Associated with other metamorphic rocks, g.neiss form large assemblies occupying about 15-20% of the surface of the earth