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How Long Do Rocks Form? Answers For ALL Types of Rocks

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There are three main types of rocks (igneous, metamorphic, and sedimentary), and the time for their formation differs dramatically from a few days to millions of years. Each type of rock has its specific conditions, which influence the time of formation. They are mostly heat, pressure, and chemical fluids.

Forming three main types of rocks (igneous, metamorphic, and sedimentary) can take 1 day to millions of years. Intrusive igneous rocks can crystallize for thousands of years, while extrusive rocks can last just a few days. It takes millions of years to form sedimentary and metamorphic rocks.

Rocks are naturally recyclable, the same as paper or cans. Metamorphic rocks, for example, can form from igneous or sedimentary rocks. After that, metamorphic rock can be changed back to a molten state and crystallize like an igneous one or can be disintegrated and deposited into sedimentary rock.

How Long Do Rocks Form?
How Long Do Rocks Form?

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How Long Does It Take For Metamorphic Rocks to Form?

Metamorphic rocks are a wide range of rocks that can be created from any type of rock, including older metamorphic ones.

The formation of metamorphic rocks requires a heat greater than 200oC and more than 300 MPa pressure. Different metamorphic rocks can be formed depending on the conditions above, and different amounts of time are needed for their formation.

It takes hundreds of thousands of years to form metamorphic rock. A specific type of metamorphic rock (impact) can be formed in a day due to a meteorite falling. Metamorphic rock is a type of rock that can be created from any type of rock, including older metamorphic rock.

The oldest metamorphic rock known is the Acasta Gneiss in the Canadian Shield. The age of this rock is estimated at 3.96 billion years old.

To understand this number and any further numbers in this article and make a comparison, the age of the Earth is approximately 4.540 to 4.520 Ga (billion years).

Metamorphic rocks are reworked already existing igneous, sedimentary, and metamorphic rocks. Here are the most common examples of metamorphic rocks:

  • igneous rock granite to metamorphic rock gneiss
  • sedimentary rock mudstone to metamorphic rock schist
  • sedimentary rock shale to metamorphic rock slate
  • sedimentary rock limestone to metamorphic rock marble
  • sedimentary rock sandstone to metamorphic rock quartzite

Creating any metamorphic rocks above requires tremendous temperature, pressure, and time. The time needed to convert one type of rock to another varies from hundreds of thousands to millions of years.

One specific type of metamorphism can create a metamorphic rock instantaneously. Impact or shock metamorphism is the process by which rocks are permanently changed due to the passage of high-pressure shock waves caused by extraterrestrial bodies – meteorites.

Pressure ranges at 100–400 GPa near the impact point and 10–60 GPa in large volumes of the surrounding rock. Temperatures are generally greater than 1000°C.

How Long Does It Take For Metamorphic Rock To Turn into Magma?

Metamorphic rocks can either remain as metamorphic rocks or they can follow one of three paths:

  1. melting, 
  2. uplift and weathering, 
  3. or subduction. 

Only the subduction can transform metamorphic rock into magma.

It takes millions of years for metamorphic rock to turn into magma. Very specific conditions should be met where metamorphic rock can turn into magma. The main is subduction zones, where Earth’s tectonic plates dive back into the mantle with a speed of several centimeters per year).

Metamorphic rocks to be converted into magma have to be subducted under continental crust. It looks like diving one plate (the harder and heavier one) under another.

This process occurs in the Ring of Fire, called the Circum-Pacific Belt. It encircles the Pacific Ocean. Subduction occurs in the western part of Northern America, the Southern American continent, and the western part of Asia and Oceania.

Melting is simply the result of continued heating and leads to magma production and, thus, new igneous rocks when the magma cools. 

The process above describes the classical rock cycle, where one type of rock is transformed into another. It takes a lot of time for the rock to make one circle.

How Long Does it Take For Quartzite to Form?

It takes several million years for quartzite to be formed from the initial sandstone. Quartzite is a non-foliated metamorphic rock composed purely of quartz. Initial sandstone is transformed into a metamorphic rock (quartzite) due to high pressure and heat.

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How Long Does It Take For Sedimentary Rocks to Form?

Sedimentary rocks are the most abundant rocks covering the Earth’s surface. That is why the wrong thought that they form very quickly can mistakenly occur.

Sedimentary rocks require the greatest period to be formed, as there are a lot of stages of formation that should be passed.

It takes millions of years for sedimentary rocks to form. The average depositional rate for sedimentary rock is millimeters per thousand years. So, it takes a lot of time to complete all stages of sedimentary rock formation: transport, deposition, sedimentation, compaction, and cementation.

There are five stages of sedimentary rock formation:

  • weathering 
  • erosion  
  • transportation
  • deposition 
  • lithification (diagenesis)

Each stage of the process takes hundreds of thousands of years. There can be pauses between stages where sediments were not deposited. Or the process could stop at one stage or another, and thousands of years would be in vain.

Sedimentary rocks are formed particle by particle and layer by layer. The layers are piled one on top of the other. Thus, in any sequence of layered rocks, a given bed must be older than any bed on top of it.

This Law of Superposition, created by the Danish scientist Nicholas Steno, is fundamental to the interpretation of Earth history. At any one location, it indicates the relative ages of rock layers and their fossils.

A geologist typically estimates the age of an outcrop of rock by looking at fossils present or by measuring the decay of a radioactive isotope

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How Long Does It Take For a Sedimentary Rock to Turn into a Metamorphic Rock?

Once sedimentary rocks are buried to depths exceeding approximately 5 to 10 kilometers, they encounter sufficiently high pressures and temperatures to undergo metamorphism, forming new rocks.

Metamorphism primarily involves the reorganization of the constituent elements within the minerals present in a rock. This process leads to the development of a new set of minerals more closely aligned with equilibrium conditions at elevated temperatures and pressures.

The transformation of sedimentary rock into metamorphic rock is a gradual process that unfolds over millions of years. The pressure exerted from the sides or the weight of overlying rocks plays a crucial role in this transformation. Just envision the immense amount of rock needed to generate temperatures of at least 200°C through pressure and heat combined.

Sedimentary rock can go in different ways and be turned into metamorphic rock. One of the next factors should be met:

  • Deep burial is one way of obtaining the heat necessary for metamorphism;
  • The heat from magma is another important agent in metamorphism
  • A great deal of metamorphism also occurs near convergent plate boundaries

FAQ: How Long Does it Take For Limestone to Form?

Limestone formation typically occurs within less than a million years of deposition in a water environment. The concentration of dissolved carbon and calcium are the main factors influencing the speed of limestone formation. A stable supply of critical elements makes limestone form faster.

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How Long Does It Take For Igneous Rocks to Form?

How Long Does It Take For Igneous Rocks to Form?
How Long Does It Take For Igneous Rocks to Form?

Igneous rocks are primarily formed from magma (molten substance). Minerals crystallize from magma, creating igneous rocks. Depending on the depth of solidification, two types of igneous rocks are differentiated: 

  • intrusive – solidify deep beneath the surface and 
  • extrusive – reach the surface and solidify under the surface conditions.

Igneous rock formation can take from thousands to millions of years in the case of intrusive igneous rocks, which slowly crystallize deep beneath the surface, and up to several days in the case of extrusive igneous rocks, which erupt in the form of lava to the surface.

When rocks are pushed deep into the Earth, they can melt to form molten rock. Below the surface of the Earth, molten rock is called magma, but when erupted above the ground, usually through volcanoes, it is called lava.

Intrusive igneous rocks of solidified magma (granite, diorite, gabbro, peridotite) cool for thousands of years. This slow cooling rate allows better development of mineral crystals. Intrusive igneous rocks will have visible crystals and will appear coarse-grained.

Extrusive igneous rocks (basalt, rhyolite) form when lava reaches the surface of the Earth through volcanoes or fissures. The rocks are formed as a result of lava cooling and hardening. Because of rapid cooling, extrusive rocks do not have enough time to form giant crystals.

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How Long Does It Take For Intrusive Igneous Rock to Form?

Intrusive igneous rocks are huge masses of hot magma enclosed deep beneath the surface under tremendous pressure. It takes a lot of time to cool giant masses of magma.

The cooling time strongly depends on the volume of the intrusive body (pluton), the intrusion’s depth, and the magma’s chemical composition. The bigger the body (it can reach thousands of square kilometers) and the dipper it is located  – the slower it is cooling.

Intrusive igneous rocks are initially huge hot (800 – 1200 oC) masses of magma. They slowly solidify deep beneath the surface. Their crystallization can take from thousands to millions of years. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have well-formed crystals. 

Intrusive igneous rocks are so giant that they can occupy many countries and continents, such as the Canadian Shield, the Baltic Shield, and the Australian Shield.

These geological structures are listed so you can see how big intrusive rocks can be, and that is why millions of years of cooling don’t seem so slow.

Because of slow cooling, minerals have more than enough time to form crystals, so the texture of intrusive igneous rocks is commonly coarse-grained with well-distinguished minerals. 

How Long Does it Take For Granite to Form?

Granite is an intrusive igneous rock that can take thousands of years to several millions of years to crystallize. Considering that the youngest known Takidani granodiorite is 1.2 million years old, granite can form faster than 1 million years. 

How Long Does It Take For Extrusive Igneous Rocks to Form?

Extrusive igneous rocks are formed from lava. Lava cools down very quickly because the temperature on the surface is low. Sometimes, lava can erupt into the water, which makes the cooling process even faster.

Depending on the thickness of lava (magma that reaches the surface), extrusive igneous rocks (basalt, rhyolite) can solidify in several years only. For example, a 20–30 m thick flow solidifies in about 2.5–6 years. 55 m thick lava flow may take roughly 20 years to reach a solid state.

New ocean crust production is a result of extrusive igneous rock formation. New ocean crust is produced at mid-ocean ridges, where two plates diverge (move in opposite directions) from each other.

In response to the divergent motions, mantle material rises to fill the void. This molten material, magma, erupts on the seafloor (becoming lava as soon as it reaches the surface) and cools below the seafloor to form a new oceanic crust. 

How Long Does it Take For Basalt to Form?

Unlike metamorphic and sedimentary rocks, basalt can be formed extremely quickly as an extrusive igneous rock. Depending on the thickness of the lava flow and the temperature of the environment, it can solidify, and, as a result, basalt can be formed within a few days or a couple of weeks.

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How Long Does It Take For Igneous Rock to Become a Metamorphic Rock?

Igneous rocks are the toughest and most resistant to weathering and disintegration among all rock types. Their closely interlocked and tempered crystals demand substantial efforts to alter.

The transformation from igneous to metamorphic rock is a process that unfolds over an immense period, ranging from hundreds of thousands to millions of years. Igneous rocks, characterized by their exceptional hardness and resilience, require significant forces for metamorphosis. Pressure emerges as the primary agent driving this transformative process.

Extrusive igneous rocks, like sedimentary rocks, typically form at or near the Earth’s surface. Consequently, they often necessitate burial to undergo metamorphism.

Intrusive igneous rocks, also known as plutonic rocks, such as granite, undergo metamorphism. However, unlike other rock types, they tend to undergo minimal mineralogical changes. This is because the minerals comprising granites are relatively stable at high temperatures, having formed under such conditions.

How Long Does it Take For Gneiss to Form?

Gneiss is a high-grade metamorphic rock formed by granite or sedimentary rock’s metamorphosis (high temperature and high pressure). It takes millions of years and temperatures over 600 °C at pressures between about 2 to 24 kbar to rework initial hard and resistant granite into gneiss.

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The time of rock formation can vary dramatically. Extrusive igneous rocks (andesite, basalt, rhyolite) can be formed in several days, while it takes millions of years to deposit sedimentary rocks (limestone, sandstone) and create metamorphic rocks (gneiss, marble).

Geologists usually operate with rocks’ relative and numeric age, not paying attention to how long it takes to form a rock. 

The hundreds of thousands to millions of years we discussed in this article give us a clue to understanding that our planet is constantly in action.

Billions of tons of rocks are reworking one to another every day deep beneath our feet. The sand we sunbathed and the limestone we made our homes of went a long way to gain the form we observe now. It takes hundreds of thousands of years for rock to be formed. 

This rock cycle occurs in millions of years and cannot be observed by humans. But this rock cycle allows us to see that our planet is active and evolving, not only a piece of rock in space. Pick up any stone and try to imagine how old it is.

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