<p>This is the key:</p>
<blockquote>
<p>used to be part</p>
</blockquote>
<p>It is important to look at this in a historical context. Up until the 1950s and early 1960s, there was no agreement to how granites form. This became the <a href="https://duckduckgo.com/?q=granite%20controversy&amp;t=ffab&amp;ia=web" rel="nofollow noreferrer"><strong>granite controversy</strong></a>.</p>
<p>On the one hand, experimental work showed that granites crystallise from magma, but this magma had to be derived from basalt-like magmas. This led to two problems:</p>
<ol>
<li>Where is all the basalt from which the granite was supposed to form?</li>
<li>What happened to all the rock that was there before the granite formed (aka the &quot;room problem&quot;)?</li>
</ol>
<p>This led people to think that granites formed by <a href="https://en.wikipedia.org/wiki/Metasomatism" rel="nofollow noreferrer">metasomatic</a> replacement of other rocks. Essentially, you have other things that were not granite that were transformed to granite through various geological process, without ever crystallising from magmas. This is what people say when they talk about granites as metamorphic rocks.</p>
<p>However, this is not the case and later research demonstrated that granites form by crystallisation of magma and the process of metamorphic formation of granites (by metasomatism, or &quot;granitisation&quot;) does not actually exists. There were (and still are) many questions left unanswered on exactly how this happens, but we know granites are indeed igneous rocks. In fact, there's a <a href="https://doi.org/10.1038/s41586-018-0746-2" rel="nofollow noreferrer">great paper</a> published in Nature, showing modelling of how some of these things can form.</p>
<hr />
<p>Nevertheless, granite formed can be sometimes related to metamorphism. Extreme cases of hot metamorphic can cause melting of (previously sedimentary and then metamorphic) rocks to form magma that eventually crystallises as granites. This is known as <a href="https://en.wikipedia.org/wiki/Migmatite" rel="nofollow noreferrer">migmatisation</a>, and is commonly used to explain the widespread occurrence of &quot;leucogranites&quot; in the Himalayas for example.</p>
<p>Additionally, some high-grade metamorphic rocks contain quartz, feldspars, micas, and amphiboles. The metamorphic texture (foliation and lineation) is not always obvious, making it easy to mistake metamorphic gneisses as igneous granites.</p>

CC BY-SA 4.0
2018-12-07T23:47:51.143Z
2021-09-29T15:40:48.813Z
2021-09-29T15:40:48.813Z
Gimelist
<p>Metamorphic rocks occur when Rocks undergo geochemical changes whilst buried under layers of stratolith above.
Ex: Marble is a rock occurs when calcium and Carbonate rich rock (chalk, limestone, etc) gets geologically pressed and converted.</p>
<p>Granite occurs naturally without such forces and can manifest fresh from volcanic eruption thou rare.</p>

CC BY-SA 4.0
2021-09-30T13:37:03.833Z
Two comments: 1/ Your definition of metamorphism is quite narrow, pressure (P) is not the only agent involved, temperature (T) is as well, that's why you have facies like HP-LT, etc. 2/ Granite *never* occurs from volcanic eruptions. If a granitic melt erupts at the surface, you'll get a (fine-grained) rhyolite, never the coarse-grained texture of a granite.
Jean-Marie Prival
CC BY-SA 4.0
2021-09-30T04:55:39.060Z
2021-09-30T04:55:39.060Z
LazyReader
<p>According to google, granite is an igneous rock. And as I said in my comment, it has several different other minerals that are formed within it, such as quartz or feldspar.</p>
<p>Some people may tell you that granite is a sedimentary rock, but based on the way it is formed (by magma cooling beneath the earths' surface) it is considered    an igneous rock.</p>
<p>More information at <a href="https://geology.com/rocks/granite.shtml" rel="nofollow noreferrer">geology.com</a>.</p>

CC BY-SA 4.0
2020-02-15T02:40:45.267Z
I don't think this deserved so many downvotes! I gave a +1 just now! I looked at your profile and saw you committed to the Protein Modeling proposal on Area51. Sorry that it didn't succeed. I proposed a [Materials Modeling](https://area51.stackexchange.com/proposals/122958/materials-modeling?referrer=NzE1MWZiMjg1NmE1MDU4YWQ2ODkzMzZiNGY5OTRkNWRhN2JkNzdhZGUwODllOWUxNGNjZjRhZjBmYTE3M2M4ZBljSouiYXUzpNjPv6N_DNmpFSwSGHCb4w8-XBwHc-_E0) site which covers protein modeling, but also other materials like solar cells, photo-voltaics, energy storage materials, new developments in batteries, and lighter or
user1271772
CC BY-SA 4.0
2020-02-15T02:40:47.953Z
stronger materials for cars, airplanes, spaceships, etc. It would be very lovely to have you in the Private Beta! Please commit if you don't think it would be inconvenient!
user1271772
CC BY-SA 4.0
2018-12-07T14:18:45.243Z
2021-09-28T22:30:29.190Z
2021-09-28T22:30:29.190Z
Eevee
<p>In my old textbooks, <strong>granites</strong> used to be part of the <strong>metamorphic</strong> rocks.<br>
Is this still true or not ? If not fully true, to which extent ?<br>
Could someone point me towards clear examples or definitions showing they are considered <em>not metamorphic</em> rocks any more ?  </p>

<p>If not metamorphic, please which part of the rock classification do they belong to exactly ?</p>

<p>Thanks,   Gilbert.</p>

CC BY-SA 4.0
2018-12-05T16:46:37.227Z
Hello Treblig, it may help to give background with a reference/quote if you happen to be able to
JeopardyTempest
CC BY-SA 4.0
2018-12-07T14:07:28.470Z
For starters, if you search 'is granite a metamorphic rock' google already tells you that granite is composed of mainly quartz and feldspar with minor amounts of mica, amphiboles, and other minerals. Some of these rocks are usually found inside other rocks or ores.
Eevee
<rocks>
Could one say that granites are metamorphic rocks, or not at all?
Treblig
# Could one say that granites are metamorphic rocks, or not at all?

(Asked by: username_0 on 2018-12-05)

In my old textbooks, **granites** used to be part of the **metamorphic** rocks.  
Is this still true or not ? If not fully true, to which extent ?  
Could someone point me towards clear examples or definitions showing they are considered *not metamorphic* rocks any more ?

If not metamorphic, please which part of the rock classification do they belong to exactly ?

Thanks, Gilbert.

**Tags:** rocks

> **Comments:**
> **username_1**: Hello username_0, it may help to give background with a reference/quote if you happen to be able to  
> **username_2**: For starters, if you search 'is granite a metamorphic rock' google already tells you that granite is composed of mainly quartz and feldspar with minor amounts of mica, amphiboles, and other minerals. Some of these rocks are usually found inside other rocks or ores.  

---

## 3 answers

### Answer by username_3 on 2018-12-07. Score: 12

This is the key:

> used to be part

It is important to look at this in a historical context. Up until the 1950s and early 1960s, there was no agreement to how granites form. This became the [**granite controversy**](https://duckduckgo.com/?q=granite%20controversy&t=ffab&ia=web).

On the one hand, experimental work showed that granites crystallise from magma, but this magma had to be derived from basalt-like magmas. This led to two problems:

1. Where is all the basalt from which the granite was supposed to form?
2. What happened to all the rock that was there before the granite formed (aka the "room problem")?

This led people to think that granites formed by [metasomatic](https://en.wikipedia.org/wiki/Metasomatism) replacement of other rocks. Essentially, you have other things that were not granite that were transformed to granite through various geological process, without ever crystallising from magmas. This is what people say when they talk about granites as metamorphic rocks.

However, this is not the case and later research demonstrated that granites form by crystallisation of magma and the process of metamorphic formation of granites (by metasomatism, or "granitisation") does not actually exists. There were (and still are) many questions left unanswered on exactly how this happens, but we know granites are indeed igneous rocks. In fact, there's a [great paper](https://doi.org/10.1038/s41586-018-0746-2) published in Nature, showing modelling of how some of these things can form.

---

Nevertheless, granite formed can be sometimes related to metamorphism. Extreme cases of hot metamorphic can cause melting of (previously sedimentary and then metamorphic) rocks to form magma that eventually crystallises as granites. This is known as [migmatisation](https://en.wikipedia.org/wiki/Migmatite), and is commonly used to explain the widespread occurrence of "leucogranites" in the Himalayas for example.

Additionally, some high-grade metamorphic rocks contain quartz, feldspars, micas, and amphiboles. The metamorphic texture (foliation and lineation) is not always obvious, making it easy to mistake metamorphic gneisses as igneous granites.


---

### Answer by username_4 on 2021-09-30. Score: -2

Metamorphic rocks occur when Rocks undergo geochemical changes whilst buried under layers of stratolith above.
Ex: Marble is a rock occurs when calcium and Carbonate rich rock (chalk, limestone, etc) gets geologically pressed and converted.

Granite occurs naturally without such forces and can manifest fresh from volcanic eruption thou rare.

> **Comments:**
> **username_5**: Two comments: 1/ Your definition of metamorphism is quite narrow, pressure (P) is not the only agent involved, temperature (T) is as well, that's why you have facies like HP-LT, etc. 2/ Granite *never* occurs from volcanic eruptions. If a granitic melt erupts at the surface, you'll get a (fine-grained) rhyolite, never the coarse-grained texture of a granite.  

---

### Answer by username_2 on 2018-12-07. Score: -2

According to google, granite is an igneous rock. And as I said in my comment, it has several different other minerals that are formed within it, such as quartz or feldspar.

Some people may tell you that granite is a sedimentary rock, but based on the way it is formed (by magma cooling beneath the earths' surface) it is considered an igneous rock.

More information at [geology.com](https://geology.com/rocks/granite.shtml).

> **Comments:**
> **username_6**: I don't think this deserved so many downvotes! I gave a +1 just now! I looked at your profile and saw you committed to the Protein Modeling proposal on Area51. Sorry that it didn't succeed. I proposed a [Materials Modeling](https://area51.stackexchange.com/proposals/122958/materials-modeling?referrer=NzE1MWZiMjg1NmE1MDU4YWQ2ODkzMzZiNGY5OTRkNWRhN2JkNzdhZGUwODllOWUxNGNjZjRhZjBmYTE3M2M4ZBljSouiYXUzpNjPv6N_DNmpFSwSGHCb4w8-XBwHc-_E0) site which covers protein modeling, but also other materials like solar cells, photo-voltaics, energy storage materials, new developments in batteries, and lighter or  
> **username_6**: stronger materials for cars, airplanes, spaceships, etc. It would be very lovely to have you in the Private Beta! Please commit if you don't think it would be inconvenient!  

---

