Granodiorite is an intrusive igneous rock that generally has a medium-grain phaneritic texture (2mm to 5mm crystals), light gray in color, sometimes with a tendency to be pink, and is mainly composed of quartz, sodium plagioclase, and amphiboles (hornblende.
Properties and characteristics
Main minerals and accessories
About 60% of the total volume of the granodiorite make up the white quartzand the feldspars. Where quartz and sodium-rich plagioclase dominate at around 40%.
While potassium feldspars, mainly orthoclase, is between 10% and 35% of the entire volume of feldspars. With respect to ferromagnesian minerals, hornblende, biotite, and augite are common.
As accessory minerals it sometimes occurs accompanying muscovite, magnetite, sphene, zircon, apatite and allanite.
Chemical composition
The granodiorite It is an intrusive igneous rock that belongs to the group of igneous rocks of intermediate to felsic composition.
In other words, it has between 52% and 63% silica (SiO2) and presents an aluminum enrichment of approximately 16% due to its plagioclase content. However, with respect to silica, its composition can sometimes be close to 60% SiO2.
The iron oxide (FeO) content is usually found on average at 3%, because ferromagnesian minerals are not the dominant ones.
Texture
The granodiorite Together with the granite, it forms the large batholiths that are located more than 5 kilometers deep below the surface. Therefore, their characteristic texture is phaneritic that varies from medium to coarse grain (2mm to 30mm), and they are very rare when their crystals measure less than 2mm.
Color
They usually have a light gray, whitish color and sometimes a little pink if it has a high percentage of potassium feldspar. Thus, when they have less than 5% of dark ferromagnesian minerals, it is said to be a leucogranodiorite and when they have more than 25% of dark minerals, it is said to be a melanogranodiorite.
Origin and formation
The granodiorite It forms the roots of large mountain ranges such as the Andes, but it is also part of the large continental cratons.
Therefore, they originate from a magma of intermediate composition generated by the partial fusion of rocks of the oceanic slab and rocks that make up the earth’s crust.
In other words, in volcanic arcs they are related to subduction and in cratons to partial melting of the upper mantle and crystallization in an intermediate silica environment.
How to identify granodiorite?
The granodiorite it is a rock that has a tendency to be very similar to granite. However, this rock has a lower percentage of alkaline feldspars compared to granite. Furthermore, muscovite is more common in granite than in stone. granodiorite.
The color is another property that can help you, since it is usually light gray to whitish and does not tend to be pink much. The look of the granodiorite it is marked by the abundant wide tabular crystals of idiomorphic plagioclase.
Uses and applications
- If the rock mass that makes up the granodiorite it is affected by harmonically spaced joints (fractures), it is used to obtain tiles.
- The tiles made with this rock serve as floor coverings, countertops and exteriors in buildings or houses.
- The large rock blocks are polished for ornamental use and funerary monuments.
- It is also used as crushed stone in road fills (road ballast).