Granite, is it a real granite?
We are often confused about what is a material sold as granite, which can lead to misunderstandings between the seller and the buyer.
Well, there are no deceptions, only nuances in the word “granite”, between the geological name and the accepted commercial name.
The geological name of a rock is based on its petrographic characteristics and its mineralogical composition. However, certain rocks are grouped commercially with a similar technical behaviour.
In the natural stone sector the word “granite” is used for a group of rocks, but in the technical specifications of each variety the petrographic definition is always included.
The American regulation (ASTM), divides the rocks for use as natural stone (dimension stone) into five groups: granite, marble, slate, sandstone / quartzite and limestone. The commercial name “granite” is used for crystalline rocks with feldspars, where generally the grains are visible to the naked eye. That includes:
- Plutonic igneous rocks more or less acidic such as granite, granodiorite, monzonite, syenite, gabbro, anorthosite and all other igneous intermediates, which differ mainly in the relative percentage of quartz, potassium feldspar and plagioclase.
- Volcanic igneous rocks such as basalt, andesite, dacite…
- Filonian rocks such as diabases
- Metamorphic rocks, generally with coarse grains such as gneisses, migmatites, granulites…
Sometimes the term “black granite” is also used, which geologically corresponds to very poor or exempt rocks in quartz, such as gabbros, anorthosites, andesites, peridotites, pyroxenites or some diabases.
Here are some examples of our CKP catalog:
The following table shows the correspondence between commercial and geological terms according to the ASTM: