Is Granite Permeable? (ANSWERED)

The short answer to this question is yes, granite is considered permeable.

However, granite is considered a mineral with one of the lowest levels of permeability.

I will detail below questions about the permeability of granite, as well as provide clear and concise definitions and examples of permeability and outline just what factors a mineral’s ability to hold water.

Is Granite Permeable? (EXPLAINED)

Characteristics of Granite

Granite is light-colored, ranging from red, pink, gray, white, igneous, and platonic rock with large enough, visible, dark grains that can be seen by the untrained eye.

It is formed by the crystallization of magma below the Earth’s surface, usually in mountainous regions, or high above the seabed, over time.

Granite is mainly composed of 65 to 90 percent feldspar (rock-forming silicate material) and between 10 and 50 percent of quartz (an abundant chemical compound of one part silicon and two parts oxygen), but can also contain mica, amphiboles, and other different minerals.

Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels, and have a very dense silica content and are highly resistant to decay.

While granite is nearly always massive and lacking any internal structures, hard, and tough, small dikes (sheets of rock that are formed from a fracture of a pre-existing rock body) of granitic composition called aplites are associated with margins of granite intrusions.

In some locations, coarse-grained pegmatite (formed from water that separates from magma in the late stages of crystallization) masses occur within the granite.

Granite is widely used for construction, which will be detailed much further, later.

The average density of granite is between 2.65 and 2.75 g/cubed cm, compressive strength is above 200 MPa (Mega Pascals), and viscosity near STP (standard temperature and pressure) is between 3-6.

Granite itself is not soluble in water.

However, over time through a process referred to as weathering, acids present in the air and in groundwater will attack the minerals that makeup granite (quartz, feldspar, mica, amphiboles, etc.) and will very slowly convert those minerals into clays.

Thus, what this question really boils down to, is what environment the granite is found in, what lays on the surface of the granite, and what condition it is found in.

Basics About Permeability

Permeability at its very basic level is the allowance of liquids or gases to pass through a certain material or membrane.

In the study of rocks specifically, permeability suggests the existence of pores or empty spaces in the rock, and if those pores are connected, therefore allowing fluid to pass through.

If the fluid can move through the rock, then that rock is considered permeable.

For example, gravel and sand are often thought of as the minerals with the highest level of permeability, and unfractured, intrusive, igneous, and metamorphic rock is often thought to have the lowest permeability.

So, minerals that are extremely dense and solid are not, or much less permeable, and those that are loose and dispersed are often the most permeable.

Porous refers to the number of pores that can be found on the surface of any material.

As talked about above, the number of cracks, pores, or breaks on the surface of a mineral, can lead to an increase in the permeability of a substance.

The more cracks, pores, and breaks a mineral has, the more water can get in, thus why granite is thought to be a mineral of significantly lower permeability.

On the surface of granite are tiny little, microscopic voids, or microvoids, that affect permeability.

Surfaces that are frequently wet, such as kitchen countertops, sink countertops, bathrooms, and others, are generally made with granite because of their low level of permeability.

Applications of Granite’s Permeability

So, while granite does have a low level of permeability, it is in fact permeable.

This makes it incredibly useful for new environmental initiatives such as GraniteCrete.

GraniteCrete is an environmentally friendly paving material alternative to asphalt and concrete.

Asphalt and concrete do not allow water to pass through and are impermeable substances. This creates runoff and pollution in nearby areas.

When stormwater flows along concrete and asphalt paved paths, the water picks up toxins, metals, and bacteria, eventually seeping and contaminating the natural groundwater supply. Permeable paving material allows water to pass through, therefore reducing the number of toxins, metals, and bacteria that accumulate.

Materials such as GraniteCrete help groundwater reservoirs by reducing environmental damage caused by runoff, acting instead as a filtration system for natural rainwater, allowing the soil and microbes below to filter out any of those pollutants before it has a chance to contaminate.

Another real-world application that benefits from the permeability of granite is a material referred to as decomposed granite.

When granite endures weathering and begins to erode, over time, it begins to dissolve, flake, and crumble away.

It can be further crushed and made into a powder-like substance.

This decomposed granite substance serves many different purposes for patios, ballparks, driveways, pathways, trail systems, and landscapes to name a few.

Decomposed granite is manufactured and sold by companies around the world, like Kafka granite, and is advertised as a low-cost, more environmentally friendly, alternative to concrete and asphalt.

Granite has been used for thousands of years for interior and exterior work.

Rough-cut and polished granite is used in buildings, bridges, paving, monuments, and other exterior projects.

Indoors, polished granite slabs and tiles are used to tile floors, stair treads, and other practical and decorative functions.

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