A Geologist’s Definitive Guide to Granite Rock (2024)

Granite is a coarse-grained, light-colored, plutonic, or intrusive igneous rock. It is dominated by alkali feldspar, quartz, and plagioclase, with other minerals like amphibole, mica, muscovite, etc., occurring in minor amounts.

The name granite comes from the Latin word granum, meaning grain, referring to the grainy texture. This rock has large, more or less equigranular grains.

Did you know that granite and other rocks like diorite, gabbro, and their extrusive counterparts – rhyolite, andesite, and basalt dominate the Earth’s crust? Now you do.

Also, you should know that this rock has many uses, including as a construction or dimensional stone, making gravel, monuments, kitchen countertops, landscaping, etc. We have details about the various uses.

Let us look at granite rocks. We will start with the basics by giving you its appearance, texture, color, chemical and mineral composition.

Afterward, we will dive deeper to look at classifications, where we will look at the ASI and alphabet.

Towards the end, you will know how granite forms, where it occurs or is found, how it weathers, and some common uses. And for those concerned about its safety, especially in indoor uses like kitchen countertops, we have a part that will give you answers.

Quick properties or characteristics

• Name: Granite
• Rock type: Igneous
• Origin: Intrusive
• Texture: Coarse-grained or phaneritic
• Colors: Mostly gray, red, pink, or white, but may have shades of green, blue, yellow, brown, or black.
• Chemical composition: Felsic
• Silica content: 70-77 wt. %
• Density: 2.63 to 2.75 g/cm³ (164 -176 lbs. per cubic foot)
• Cooling history: Slow, deep inside the Earth’s crust.
• Melting point: 1215–1260 °C, at ambient pressure.
• Mohs scale of hardness: 6-7
• Extrusive equivalent: Rhyolite
• Metamorphized form: Gneiss
• Magnetism: Granite is not magnetic. However, those with considerable magnetite may show weak magnetism (weak magnetic susceptibility).
• Tectonic environment: Continental collision, volcanic arcs (island and continental subduction zones), continental intraplate rifts and hotspots and mid-ocean ridges

What does granite look like?

Color, texture, and fabric are key to identifying this felsic rock. Granite is usually a massive, tough, mostly off-white to gray, pink, red, yellow, and brown rock. It has large visible mottled or speckled equigranular grains with predominantly light-colored crystals (felsic) and fewer scattered dark-colored ones (mafic).

You could easily confuse it with other rocks with speckled or salt-and-pepper appearance, like gabbro, diorite, granodiorite, tonalite, syenite, monzonite, etc. However, it tends to be lighter in most cases due to the high felsic mineral amount. Also, the pink or reddish colors tend to be prominent due to higher alkali feldspar.

Besides the coarse-grained texture, granite may also be porphyritic or pegmatitic. Other less common ones are rapakivi, miarolitic, myrmekite, orbicular, and graphic granites. Also, it may show modal and layering.

Let us discuss more about colors and texture. We will also discuss modal and comb layering, common inclusions, and granitic veins.

1. Colors

Granite colors range from white to shades of gray, pink, red, yellow, and brown. Some granites may have blue, greenish, tan, or black colors.

These colors are influenced by the various minerals present. For instance, felsic minerals like alkali feldspars are white, pink, or reddish, Quartz is colorless to gray, plagioclase white to greyish white, and muscovite colorless. These felsic minerals will impart these colors.

On the other hand, mafic minerals make the darker grains. Biotite is black to dark brown, hornblende is black to dark green and pyroxenes are black to dark green, brown, or black.

The usual granite color index is 5 < M < 20, with darker minerals less than 20% by volume. Leucogranite has M < 5 and appears white or light-colored with nearly no dark or mafic minerals.

On the other hand, melagranite describes a granite darker than usual, even if it has fewer mafic minerals by volume. For instance, the dark-green-brown potassic feldspar common in ferroan granites and syenites may be a reason for the dark colors, notes Blatt et al. (2006)

2. Texture

Granite usually has a coarse-grained or phaneritic texture. However, it may be porphyritic or pegmatitic, with graphic, myrmekite, orbicular, miarolitic, and rapakivi textures less common.

This rock often has nearly equigranular interlocking crystals of quartz and feldspar with fewer scattered darker minerals, giving it a speckled appearance.

The darker minerals are mica or amphibole and, less often, pyroxenes. Some authors describe this appearance as a salt-and-pepper look but it is not as pronounced as in gabbro.

In most granitic rocks, feldspars often have perthitic texture characterized by the intergrowth of unmixed feldspars. Potassic feldspar (orthoclase) hosts lamellae of sodic plagioclase intergrowths in this texture. However, in some, they can exist independently.

Furthermore, minerals in granite are hypidiomorphic (a proportion of crystals are subhedral) to hypautomorphic (where some constituents show euhedral, others subhedral, and the rest anhedral).

Let us look at some granite textures and say a thing or two.

i. Porphyritic granite

Porphyritic granite will have large (sometimes over 10 cm), usually k-feldspar (white or reddish/pinkish) crystals in the coarse-grained matrix. The groundmass may be quartz, feldspar, and mafic minerals.

The formation of porphyritic texture indicates two-stage cooling.

ii. Granite pegmatite

Granite pegmatites have unusually large crystals (up to tens of meters) formed during crystallization of the last magma or melt portions.

The buildup of dissolved water in the final part of magma to crystallize depolymerizes the melt. This prevents crystallization until it is supersaturated. Once nucleation occurs, crystals will then grow rapidly, crystallizing pegmatites.

Some granitic pegmatites may have valuable elements like tin, thorium, niobium, and REE (rare earth elements) or gemstones like tourmaline, beryl, topaz, spodumene, zircon, etc.

iii. Orbicular granite

Orbicular granite has nearly spheroidal or ovoid structures or nodules known as orbiculates (a few to 10s of centimeters). These orbiculates have concentric layers of contrasting texture and mineralogy, i.e., mafic/felsic (biotite and plagioclase).

Orbicular texture occurs due to the radial development of crystals. It infers a faster crystal growth than the nucleation rate around a xenolithic core.

iv. Graphic and myrmekite granite

Graphic granite has intimate quartz-alkali intergrowth resembling ancient runic or cuneiform inscriptions. It forms under crystallization conditions that favor simultaneous planar feldspar and rod quartz growth.

On the other hand, myrmekite granite has a wormy intergrowth of quartz enclosing sodic plagioclase.

v. Miarolitic cavities or texture

Miarolitic cavities in granitic rocks are centimeter-scale cavities, voids, or vugs common in pegmatites. These cavities are often lined with minerals like topaz, beryl, and fluorite. However, sometimes, miarolitic cavities have rock-forming minerals like quartz, feldspar, and mica.

What causes this texture? It is believed that rapid and unconstrained crystal growth into large fluid bubbles is the likely cause.

vi. Rapakivi granite

Rapakivi granite is a less common texture. It occurs mostly in biotite-hornblende (amphibole) granites and is characterized by large rounded or oval feldspars rimmed by oligoclase, a plagioclase variety.

3. Modal and comb layering

Granite may show modal and comb layering. Modal layering occurs when minerals like hornblende and biotite proportion vary in the rock.

On the other hand, comb layering resembles the teeth of combs. It often has elongated crystal layers of hornblende or plagioclase growing perpendicular to the layering plane. These crystals tend to branch or thicken inward to the pluton body.

4. Granite veins

Granite veins are sheet-like bodies up to a meter or larger with distinct minerals crystallized within a rock mass. They form when mineral-containing aqueous solutions within a rock mass precipitate.

Most veins will have a distinctive color. They may be blue, black, gray, white, etc.

5. Common inclusions

Granitoid pluton inclusions include xenolith (sedimentary, metamorphic, or igneous), enclaves (enclosed angular or rounded rock bodies with different textures or colors), restite, and schlieren.

Schlieren are inches to tens of feet tubular bodies with the same mineralogy as pluton but vary modally or in grain size. Thus, they look different.

On the other hand, restites are refractory residue fragments from the partial melting of metamorphic rocks.

Granite composition

Granite is a felsic rock relatively high in alkali oxides. Here is its chemical and mineral composition:

1. Chemical composition of granite

Granite is a silica-rich, acidic rock. It has 70-77 wt % SiO₂, 11-15% Al₂O₃, considerable alkali oxides (Na₂O and K₂O), low in mafic elements (MgO and FeO) and calcium oxide.

According to Blatt & Tracy (2006), the average weight percentage of granite based on 2485 sample analyses worldwide is SiO₂: 72.04%, TiO₂: 0.30%, Al₂O₃: 14.42%, Fe₂O₃: 1.22%, FeO: 1.68%, MnO: 0.05%, MgO: 0.71%, CaO: 1.82%. Na₂O: 3.69%, K₂O: 4.12% and P₂O₅: 0.12%.

These are only averages. The exact chemical composition may vary depending on the specific variety of granite.

2. Minerals in granite

Granite is a felsic rock. Its mineral composition is predominantly alkali feldspar, quartz, and plagioclase, with minor amounts of hornblende (amphiboles) and biotite (mica).

Also, depending on the variety, it may have muscovite, riebeckite, aegirine, aegirine-augite, arfvedsonite, ferroan augite, orthopyroxene, iron-rich olivine, etc.

Accessory minerals in granite include apatite, magnetite, zircon, titanite (sphene), topaz, tourmaline garnet (almandine-spessartine), ilmenite-hematite, monazite, allanite, and fluorite. Less common accessory minerals are cordierite, andalusite, sillimanite, pyrite, lead-bearing mica (zinnwaldite or lepidote), etc.

Granite’s primary minerals, i.e., alkali feldspar, quartz, and plagioclase, account for over 80% of granite rocks by volume,

Usually, alkali feldspar is orthoclase and less often microcline while plagioclase is oligoclase (calcic) to sometimes albite (sodic). These feldspars may form perthitic intergrowths.

Typical hydrothermal alteration includes

• Biotite → chlorite and sphene
• K-feldspar → kaolinite and sericite
• plagioclase → epidote, kaolinite, zoisite and epidote
• Pyroxenes → chlorite, uralite, or iddingsite.

Let us look more into granite, granitoids, and the QAP diagram.

1. Granitoids and granite

Granitoids or granitic rock represent a larger group of coarse-grained intrusive igneous rocks namely, granodiorite, granite, tonalite, and alkali feldspar.

On the QAP diagram, granitoids are plutonic rocks in which quartz accounts for 20-60% of QAP by volume and have variable amounts of plagioclase and alkali feldspar.

Note that we didn’t refer to the QAPF diagram as usual as these rocks don’t have feldspathoids.

Granite (sensu stricto) is a coarse-grained intrusive rock in which quartz is 20-60% QAP content by volume and alkali feldspar accounts for 35% to 90%of the total feldspar. It doesn’t have feldspathoids.

You may subdivide granite into synenogranite with 65-90% of the total feldspars alkali feldspar and mozogranite with 35-65%.

Tonalites have no more than 10% of the alkali feldspar, while in granodiorites, plagioclase accounts for 65-90% of the total feldspars.

On the other hand, in alkali feldspar granite plagioclase is less than 10% of total feldspar by volume. Alaskite is a leucocratic tonalite variety with a color index of M < 10.

While we seem to have divided them, the truth is that granitoids exhibit a continuum composition. These subdivisions are to help classify these rocks.

Another thing worth mentioning is that some authors may refer to gabbro, diorite, syenite, monzonites, and other coarse-grained plutonic rocks as granitic or granitoids. It is incorrect since granitoids must have 20-60% quartz.

Related rocks or terms include:

• Aplite: A medium to fine-grain (1mm or less) rock with mainly feldspar and quartz common in small granitic dikes and margins of larger intrusions.
• Granophyre: Granophyre is a porphyritic subvolcanic rock with a composition like granite characterized by angular intergrowths of quartz and alkali feldspar.
• Hypersolvus and subsolvus granite: Crystallization at high water pressure will form solvus granite characterized by two distinct feldspars. In contrast, hypersolvus granites crystallize at low water pressure, resulting in one feldspar characterized by exsolutiontextures, i.e., a perthitic texture.

2. Naming granitic rocks

You can use additional prefix qualifiers to name granites (textural, chemical, and mineralogical) if considerable. For instance, you can have Sr-rich, porphyritic, biotite, or two mica granite.

Also, you can use genetic terms like anatectic-granite or tectonic terms post-orogenic granite.

However, granitic rocks cannot be quartz-free and don’t have feldspathoids.

Lastly, you can use two qualifying prefixes, like hornblende-biotite granite. Name according to increasing order of relative abundance and hyphenate them. Here biotite > hornblende.

More granitoids classification

Granitoid classification based on plagioclase, alkali feldspar, and quartz (QAP) is straightforward and applicable. However, it ignores variations apart from those that affect the quartz and feldspar compositions.

This reality led to geologists finding other ways to classify granitic rocks. Popular ones are ASI and the alphabet. Other methods include the Fe-index, Modified Alkali-Lime Index (MALI), Alkalinity Index (AI), or based on the oxidation state (redox state).

1. Alumina saturation index (ASI) classification

It is based on the alumina saturation index (ASI), i.e., the molar ratio of Al₂O₃ to (CaO + Na₂O + K₂O expressed as A/CNK. It gives peraluminous, metaluminous, peralkaline, and subaluminous granitoids.

Each category is diagnostic of certain tectonic settings or magma sources and characteristic of minor minerals (tied to mineralogy). Apatite and zircon are ubiquitous in ASI classification.

i. Peralkaline granite

Peralkaline granites are aluminum deficient relative to sodium and potassium, i.e., they have less aluminum than is needed for feldspars.

In this rock, (Na₂O+K₂O) > Al₂O_3, and A/CNK<<1.

Thus, they have aluminum-free minerals like sodic pyroxenes (aegirine or acmite) and sodic amphibole (riebeckite). Also, they will have diopside (due to excess CaO), Fe-rich biotite, and albitic plagioclase.

Common accessory minerals are fluorite, titanate, thorite, and allanite. Also, these rocks have rare metal pegmatite rich in Nb, Ta, P, Cs, Y, and REE.

The Magma origin for peralkaline granites is fractional crystallization. These rocks occur in intraplate hotspots and intracontinental rifts, with a few in subduction zones.

ii. Metaluminous granite

Metaluminous granites are alumina undersaturated with A/CNK<1 but Al₂O₃ > alkalis (Na₂O + K₂O) and Al₂O₃ < Na₂O + K₂O + CaO). Thus, they have excess CaO.

These granitoids will form minerals like hornblende, clinopyroxene (diopside), sphene, biotite, epidote, melilite, and calcic amphibole. Common accessory minerals are titanite and allanite.

Lastly, metaluminous granite occurs in subduction-related settings, continental and island arcs. Those associated with Cu-Mo mineralization (copper porphyry) are found in the Andes.

iii. Peraluminous

Peraluminous granitoids are aluminum oversaturated, i.e., have more than needed to crystallize feldspar with A/CNK >1.1 and are lower in Na and higher in K.

These rocks will have aluminous phases (silicate) like cordierite, topaz, andalusite, sillimanite, muscovite, garnet (almandine), tourmaline, and biotite (aluminous like gedrite or cummingtonite). However, they don’t have diopside or hornblende since all CaO is bound to plagioclase.

Excess Al₂O₃ is expressed as normative corundum, and accessory minerals are monazite, xenotime, topaz, and uranite.

Where do they occur? Peralkaline granite occurs in the orogenic continental collision. Those in the Bolivian tin belt are associated with silver and tin.

Lastly, weakly peraluminous granites will have A/CNK = 1.0-1.1. They have clinopyroxene, hornblende, epidote or gedrite, calcic amphibole, and biotite. Their common accessory minerals are monazite, titanite, and allanite.

iv. Subaluminous

Subaluminous granite has alkalis (Na₂O + K₂O) approximately equal to alumina (Al₂O₃) with A/CNK <1. Some of these rocks’ accessory minerals include clinopyroxene, orthopyroxene, and olivine.

2. Alphabet or S-I-A-M granitoid classification

This classification was advanced in the 1970s to support different magma sources for granitoids. It considers mineralogy, isotopic characteristic \( \frac { ^{87}Sr}{^{86}Sr_i} \) and \(\delta^{18}O \), textures and geochemical properties. It can help know the magma source.

However, many geologists have voiced the need to abandon this classification for various reasons. For instance, it infers S- and I-type to certain magma sources, which vary in A-type.

Also, fraction crystallization can result in a suite of several related rocks, and the chances of granitic rock being from a single source are minimal.

Nonetheless, you need to know this classification.

i. I-type granites (I = Igneous)

I-type granites have metaluminous to weakly peraluminous tonalites, granodiorites, and granites. These rocks form from the partially melting solidified igneous rocks. Here, I stands for or infers to igneous.

Index Values: A/CNK<1.1, \( \frac { ^{87}Sr}{^{86}Sr_i} < 0.705\) and \(\delta^{18}O <9\% \)

These rocks are Rb-poor, higher in Na and CaO-rich than S-type. Also, they have biotite, hornblende, and diopsidic pyroxene, with accessories being titanite (sphene), magnetite (a commonest oxide), and allanite (a diagnostic mineral)

Lastly, they occur in continental arc margins.

ii. S-type granites (S = sedimentary or supracrustal)

S-type granites form from partially melting sedimentary and metasedimentary rocks and are mostly strongly peraluminous to metaluminous.

Index values: A/CNK> 1.1, \(\frac {^{87}Sr}{^{86}Sr_i} > 0.707\) and \(\delta^{18}O <9 \% \)

They occur in regional metamorphic terranes, including syn-collision, post-collision, and subduction-related. Also, they may form from mantle plumes from pelitic or metapelitic rocks.

Some places these rocks occur include the Eastern Andes, Sierra Nevada batholith, Peninsular Range Batholith, and all over Idaho.

Usually, S-type granitoids have aluminum-rich minerals with no hornblende. Accessory minerals are zircon tourmaline, apatite, monazite, and xenotime. Monazite is a diagnostic, and ilmenite is the common Ti mineral.

Lastly, S-type granitoids have variable LIL (large ion lithophile) and HSF (high field strength elements) and are usually high in Rb and Th. Also, they may have economically valuable Sn, W, U, Li, Be, and B deposits.

iii. M-type granitoids (M = mantle)

These granitoids are mantle-derived, i.e., form from partial melting of subducted oceanic crust. Their composition and isotopic signature resemble those of island arc volcanic rocks.

Index values: A/CNK> 1.1, \( \frac { ^{87}Sr}{^{86}Sr_i} > 0.707\) and \(\delta^{18}O <9 \% \)

They are low in HFS (REE, Th, Nb, Ce, U, Pb⁴⁺, Hf, Zr, Ti, Ta) and LIL (K, Sr, Rb, Ba, Cs, and Eu²⁺) and form from subduction zones and oceanic intraplate.

iv. A-type granites (A = anorogenic or anhydrous)

These are anhydrous, mainly peralkaline granitic rocks formed on the continental anorogenic settings, i.e., rift valleys and interiors of continental plates.

However, depending on alumina content, they can be metaluminous and sometimes peraluminous. Also, they are known to have a Rapakivi texture and are associated with alkaline basalt.

Index values: A/CNK>1.0 \( \frac { ^{87}Sr}{^{86}Sr_i} \) and \(\delta^{18}O \) comparable to other types

A-type granitoids are silica-rich and higher in alkalis than I- and S-type. Also, they have a high K₂O/Na₂O and Fe/(Fe+Mg) ratio but are low in CaO.

Their mafic content is green biotite, Na-pyroxenes, Na-amphiboles, and hedenbergite with no muscovite. Common accessory minerals are fayalite and titanite.

Lastly, an essential geochemical characteristic of A-type granitoids is the high concentration of incompatible elements like cerium, zinc, zircon, yttrium, niobium, gallium, and heavy REE (except Eu).

How does granite form?

Granite forms from the slow cooling of granitic magma deep inside the Earth’s crust, i.e., inside magma chambers known as plutons. The slow cooling allows crystal growth (ions, atoms, or molecules to arrange themselves), forming large, visible crystals. Also, these conditions favor crystal growth over nucleation.

Granitic magmas are silica-rich (> 69% SiO₂), and low in MgO and FeO. These magmas form by 1) partially melting pre-existing subcrustal rocks or 2) fractional crystallization of mafic magma derived from the mantle. Their high silica content makes them highly viscous since silica polymerizes.

Lastly, erosion and uplift may expose granite rock outcrops, inselbergs, domes, cliffs, and mountains. Otherwise, they would not be visible.

Where is granite found?

Granite rocks are widespread on all continents and are found in all tectonic settings. They are common in continental crusts, especially orogenic (mountainous) zones, with considerable amounts found in anorogenic continental (rifts and hotspots) volcanism.

Also, some granitic rocks occur in oceanic islands with small volumes found in mid-ocean ridges and ophiolites.

Usually, granite forms intrusive igneous bodies or plutons like sills, dikes, laccoliths, lopoliths, stocks, and batholiths. They occur with associated volcanic rocks like gabbro, granodiorite, tonalite, diorite, and quartz monzonite. Also, plutons may have metamorphosized granitic rocks.

Pluton sizes range from inch-scale dikes or sills to thousands of kilometers (1000 km² with volumes of 1 km³ to 10⁶ km³).

Large granitic plutons in the US include the Sierra Nevada (California), Idaho batholith, Coast Range Batholith, Peninsular range, Wallowa Mountains, Wyoming batholith, and Enchanted Rock.

Here is a table of granitic rocks in various tectonic settings, including examples.

How does granite weather?

Like other rocks, granite weathering is mainly chemical and physical. However, biological including plant rooting and animal movement, can cause weathering too.

Temperature changes (cause expansion and contraction), salt, rain, ice, wind, and action of waves can cause physical or mechanical weathering. This will result in pitting, sheeting (exfoliation), flaking, cracking, block splitting, etc.

On the other hand, chemical weathering will involve hydrolysis, such as a reaction of potassium feldspar (orthoclase) with water or weak carbonic acid to form kaolinite (a clay mineral).

This granular disintegration creates angular, coarse-grained sand and gravel or grus. Also, the hydration of biotite will result in smectite accompanied by iron oxidation.

What is granite used for?

Granite is a hard (resist abrasion), highly durable inert stone with high compressive energy. Also, it takes good polishing, is thermally resistant, and doesn’t easily crack when heated, among many other properties.

These properties and many others make granite ideal for making dimension stones, construction aggregate, memorial monuments, paving, curbing, landscaping, etc.

Here are some of the common uses of granitic rocks:

1. Gravel and aggregate

Crushed granite, i.e., gravel or aggregate, is used for making roads, railroad beds, buildings/structures, or concrete. Also, it makes subbases, base material, sewer medium, and decorative chippings in planters or flowerbeds, etc.

More uses include making granite sand for patios, driveways, and walkways and screening for landfilling. Also, granite sand or grit may be perfect for chicken coops, fireplaces (firepits), etc.

Larger crushed stones can work as decorative landscaping boulders or ripraps to control erosion.

That is not all. Granite dust is good for soil amendment, laying artificial grass, etc. However, use masks when handling the dust since it has crystalline silica that is potentially carcinogenic (cause silicosis).

Did you know that granite is the second most crushed stone after limestone? According to the Minerals Education Coalition, it accounts for 27% (400,000 tons) of crushed rocks in the USA.

2. Dimensional stone industry

Cut-rough, polished, bush-hammered, leathered, or horned granite stones have many architectural uses in the dimension stone industry.

For instance, cut and polished granite make kitchen countertops, backsplash, bathroom vanity tops, cabinet tops, worktops, desktops, tabletops, bathtubs, slabs, windowsills, stair treads (staircases), and indoor wall or floor tiles.

On the other hand, reclaimed, hewn, polished, antiqued, or rough granite stones make steps, building blocks or bricks, outdoor pavers (including Belgian setts and cobblestones), swimming pool decks, retaining walls, etc.

Also, these stones will work well for facing bridges and buildings (façade) or as cladding panels and are more durable in curbing than concrete.

There are many buildings in the USA wholly built or partly (such as faced) using granite. Examples include Holyoke City Hall and St. Patrick’s Church (Massachusetts), Union Trust Building (Washington D.C.), and Fort Knox (Maine). Others are Salt Lake Assembly Hall(Utah), Clark and McCormack Quarry and House (Minnesota), etc.

3. Memorial monuments, headstones, and statues

Its durability and longevity make granite the first-choice material for making memorial monuments, headstones or grave markers, cemetery engraved memorial plaques, flower vases or pots, grave chippings, lanterns, candle holders, etc.

Some famous granite statues and monuments in the USA include the National Monument to the Forefathers (the largest in the USA), Mount Rushmore in South Dakota, and the Vietnam Veterans Memorial. Also, the Diana Memorial Fountain (London, UK) was made using this rock.

Lastly, you can buy granitic statues, including Ganesha, eagles, Buddha, angels, lion, Krishna, etc., and decorative carvings.

4. Curling stones

Ailsa Craig granite has made curling stones since the 1750s and still accounts for over 50% of the curling stones used today. Since they are rare, one stone sells for as much as US$1,500.

5. More applications

Granite’s other uses are making plant containers (planters/pots), bowls, basins, fountains, balls, mortar & pestle, statues, steppingstones, and flagstones. Also, they make urns for human ashes, fountains, clock mantels, pillars, benches, and balls.

More uses include making fireplace surrounds, hearths, walls, and mantels.

6. Associated with valuable ores and minerals.

Volatile and thermal flux from granitic and other plutons drive hydrothermal mineralization, forming various metal-containing minerals, including copper, molybdenum, tin, tungsten, lithium, boron, etc.

For instance, Great Britain, Malaysia, and Bolivia granites contain tin, McKenzie Mountains (Canada), and Yangjiashan (South China) tungsten. Also, the Paleozoic Lachlan Fold Belt in Australia has copper, molybdenum sulfide, and pyrite veins with gold and silver.

7. Recreation

Granitic outcrops make some of the best rocks for climbers. They offer friction, are sound, steep, and have a crack system.

8. Prehistoric to medieval uses

Granite had many uses in the Neolithic and Middle Ages, including Roman monumental architecture. For instance, ancient Egyptians used it to make statues like the colossal red granite statue of Amenhotep III, Ramesses II red granite statue, vases, and columns.

Also, Egyptians used it to make pyramids like the Pyramid of Menkaure, the Great Pyramid of Giza, and the Black Pyramid. Also, they made sarcophagi, beams, boxes, floor and wall veneers, door jambs, sills, and lintel.

Other ancient monumental granite buildings are the Korean Seokguram Grotto Buddhist shrine (UNESCO World Heritage in 1995 List) and the Indian Brihadeeswarar Temple.

Is granite rock radioactive? – Radiation risks

Like many other rocks, granite rocks may have trace radioactive elements like uranium and thorium in their veins. These radioactive elements undergo decay to form radon.

Radon is a colorless, odorless radioactive gas, which, if inhaled over time, increases the risk of developing lung cancer. This fact concerns people with granite indoor countertops, slabs, worktops, tiles, etc.

Levels or how much radiation granite emits varies with each rock unit. Thus, it is good to get a DIY radon test kit at home or call 1-800-SOS-RADON (767-7236). Acceptable levels are 2 pCi/L to 4 pCi/L.

However, as the Environmental Protection Agency (EPA) notes, sealing granite stones prevents escape. Also, “radon originating in the soil beneath homes is a more common problem and a far larger public health risk than from granite building material.”

Frequently Asked Questions (FAQs)