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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 heat, pressure, and chemical fluids mostly.

The formation of three main types of rocks (igneous, metamorphic and sedimentary) can take from 1 day to millions of years. Intrusive igneous rocks can crystallize thousands of years, while extrusive rocks 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 either igneous rock and sedimentary rock. 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.

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

How Long Does It Take For Metamorphic Rocks to Form?

Metamorphic rocks are a really wide range of rocks, as they can be created from any type of rock, including older metamorphic rock.

The formation of metamorphic rocks requires a heat greater than 200oC, and more than 300 MPa pressure. Depending on the conditions above, different metamorphic rocks can be formed, 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 as a result of 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.

For you to understand this number and any further numbers in this article to 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

The creation of any of the metamorphic rocks above requires tremendous temperature and pressure in combination with time. The time needed for the conversion of one type of rock to another varies from hundreds of thousands of years to millions of years.

There is one specific type of metamorphism, which can create a metamorphic rock instantaneously. Impact or shock metamorphism is the process by which rocks are permanently changed as a result of 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. There are very specific conditions that 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 takes place in the Ring of Fire, also referred to as the Circum-Pacific Belt. It encircles the Pacific ocean. Subduction occurs in the western part of Northern America and the Southern America continent and the western part of Asia and Oceania.

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

The process above is a description of 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.

FAQ: 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 type of rocks which cover 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 thousands of years. So it takes a lot of time to complete all stages of sedimentary rock formation: transport, deposition, sedimentation, compaction, cementation.

There are five stages of sedimentary rocks 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 on one stage, or another and thousands of years would be in vain.

Sedimentary rocks are formed particle by particle and layers by layers. 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 the fossils in them.

Most typically, a geologist 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?

As soon as sedimentary rocks are buried to depths greater than about 5 to 10 km, they experience high enough pressures and temperatures to metamorphose into new rocks.

Metamorphism is generally just a rearrangement of all the elements that make up the minerals found in a rock, in order to produce a new set of minerals that are closer to being in equilibrium at these elevated temperatures and pressures. 

It takes millions of years for sedimentary rock to turn into a metamorphic. It can happen because of pressure from the sides or from above because of the weight of overlying rocks. Imagine how many rocks you need to put in to produce heat of at least 200 oC.

Sedimentary rock can go different ways to 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;
  • 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 can be considered primary rocks as they are 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 rocks 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 are erupted in form of lava to the surface.

When rocks are pushed deep enough down 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 made of solidified magma (granite, diorite, gabbro, peridotite) cools throughout 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 big 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 time of cooling strongly depends on the volume of the intrusive body (pluton), the depth of the intrusion, and the chemical composition of the magma. 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 hudge 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 a substantial part of countries and continents, for example, the Canadian shield, the Baltic shield, the Australian shield.

These geological structures are listed for you to 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. 

FAQ: 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. Taking into account that the youngest known Takidani granodiorite’s age is 1.2 million years, 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 completely 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.

Here, 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 in place below the seafloor to form a new oceanic crust. 

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

Unlike metamorphic and sedimentary rocks, basalt, as an extrusive igneous rock, can be formed extremely quickly. 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 hardest and the most resistant to weathering and disintegration. Hudge efforts should be applied to change closely interlocked and tempered crystals.

It can take hundreds of thousands to millions of years for igneous rock to become a metamorphic one. Igneous rocks are extremely hard and resistant, so there are a lot of forces that should be applied to transform them into metamorphic rocks. Pressure is the main agent in this transformation. 

Extrusive igneous rocks, like sedimentary rocks, form at or near the surface, and so they generally require burial to undergo metamorphism. 

Intrusive igneous rocks (plutonic), like granite, also undergo metamorphism, but unlike other rocks, they generally experience little in the way of mineralogical changes since the minerals found in granites are relatively stable at high temperatures because they formed at fairly high temperatures. 

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

Gneiss is a high-grade metamorphic rock formed by the metamorphosis (high temperature and high pressure) of granite or sedimentary rock. 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.

Conclusion

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 the relative and numeric age of rocks, not paying attention to how long it takes to form a rock. 

Hundreds of thousands to millions of years we discussed in this article gives 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 are sunbathing on, limestone we are making our homes of did a long way to gain the form we observe them 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 a human. But this rock cycle allows us to see that our planet is very active and evolving, but not only a piece of rock in space. Pick up any stone and try to imagine how old it is.

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