The Three Definitions of Granite

Frederick M. Hueston  StoneForensics.com

Did you know that there are three definitions to granite?  The following are these definitions:

Granite can be defined in different ways depending on the context. Let’s explore the three common definitions of granite: commercial, geological, and US customs.

Commercial Definition: In the commercial context, granite refers to a broad category of natural stone used in construction, architectural applications, and countertops. Commercially, granite often includes a wide range of igneous rocks with varying mineral compositions. It is commonly classified as granite based on its appearance, durability, and suitability for specific applications.

This commercial definition is broader and may encompass rocks that geologically may not meet the strict criteria for granite. Commercially classified granite may include rocks that are technically gabbros, syenites, or other similar types, but they are marketed and sold as granite due to their similar appearance and performance characteristics.

Geological Definition: From a geological standpoint, granite is a specific type of intrusive igneous rock with a specific mineral composition and texture. Geologically defined granite is composed primarily of three essential minerals: quartz, feldspar (usually orthoclase or microcline), and mica (usually muscovite or biotite). It typically forms through the slow cooling and solidification of molten magma deep within the Earth’s crust.

Geologically defined granite exhibits a granular texture with visible interlocking mineral grains. The rock’s mineral composition and texture distinguish it from other types of igneous rocks. This geological definition is more precise and reflects the specific characteristics of true granite.

US Customs Definition: The US Customs and Border Protection (CBP) has its own specific classification for granite. According to the CBP, granite is defined as “a crystalline rock consisting of quartz, feldspar, and mica.” This definition aligns with the geological definition but simplifies the criteria for customs purposes.

The CBP definition focuses on the three primary minerals present in granite and is used to differentiate granite from other rocks and materials during import/export processes.

There are three common definitions of granite: the commercial definition, which encompasses a broad range of natural stones used in construction and countertops; the geological definition, which refers to a specific type of intrusive igneous rock with quartz, feldspar, and mica; and the US Customs definition, which simplifies the geological criteria to classify granite for import/export purposes.