<p>It would completely depend on location. For instance, Sawtooth mountains in Idaho is a very large granite batholith so the rock in the tunnel would igneous granitic rock with varying textures and crystal sizes.  You need to define a geological setting for the location first.<br>
 - Pacific Northwest - volcanic rock, large volcanic peaks.
 - BlackHills of SD - Granitic core surrounded by metamorphic sedimentary rocks  and unlatered sedimentary rocks.</p>

<p>My recommendation is check out a couple of the Roadside Geology of .... books. These books are written in layman terms with explanations of the geology.<br>
See Roadside geology of Colorado ISBN:087842105X</p>

CC BY-SA 3.0
2016-08-02T15:44:58.103Z
2016-08-02T15:44:58.103Z
Earth Science Expatriate
<p>As Gary mentioned, it really depends on particular context for your mountain. How did it form? Is it volcanic in nature? Or maybe just old rocks being uplifted by some episode of compression.</p>

<p>On average, Earth's crust is pretty much granite. So chances are that you will find that inside your mountain. That wouldn't be a bad assumption. Granites form by cooling magma slowly, so most volcanic-type mountains are made of granite or something similar. For example, the Andes (below) are made of fine-grained Andesite near the surface and Diorite (Andesite's coarse-grained version, which is similar to Granite, but not quite) at depth.</p>

<p><a href="https://i.sstatic.net/IsSoy.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/IsSoy.jpg" alt="enter image description here"></a></p>

<p>In the case of cooling magma to form rocks, the slower the cooling, the larger the crystals will be. So rocks that cooled near the surface, will be composed of tiny crystals while rocks that cooled deeper will have larger crystals. </p>

<p><a href="https://i.sstatic.net/hvoe6.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/hvoe6.jpg" alt="enter image description here"></a></p>

<p>You could argue for more exotic rock types but that would imply a slightly more complex geological history (which is totally possible). For example, you could have uplifted a huge package of sedimentary rocks without any volcanism involved. Or you could have simply eroded everything around leaving large rock packages like the Venezuelan Tepuis (below).</p>

<p><a href="https://i.sstatic.net/8ZTNq.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/8ZTNq.jpg" alt="enter image description here"></a></p>

<p>In general, the rocks deep inside a mountain (or simply super old rocks) have also undergone a lot of compression, so sedimentary rocks will be unlikely as you would have converted them into metamorphic rocks, e.g. limestones would be marble, sandstones would be quartzites (like the Tepuis), shales would be slates (or schists, etc.), etc.</p>

<p>Similarly, metamorphic rocks that have undergone a higher degree of compressional and thermal stress (i.e. deeper in the mountain) will grow larger crystals.</p>

<p><a href="https://i.sstatic.net/i72Yo.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/i72Yo.jpg" alt="enter image description here"></a></p>

<p>Of course, like anything in geology, other complex scenarios do exist where these rules of thumb don't work. But in general, this should get you started.</p>

<p>Anyway, hope that helps.</p>

CC BY-SA 3.0
2016-08-02T18:28:36.170Z
Exactly what I was looking for, thank you very much!
Ross Taylor-Turner
CC BY-SA 3.0
2016-08-02T16:54:38.340Z
2016-08-02T17:05:06.407Z
2016-08-02T17:05:06.407Z
Antonio
<p>I'm developing a semi-realistic game involving stereotypical dwarves digging into mountainsides and carving out grand caverns for themselves, similar to those in Moria or the Lonely Mountain from Tolkien's works.</p>

<p>I'm attempting to research what kind of layers of rock (in layman's terms) you'd expect to find in a typical non-volcanic mountain range in say, northern Europe. So far though I'm at a loss so at this point anything would be a help!</p>

CC BY-SA 3.0
2016-08-02T20:19:34.663Z
Unrelated, but [Ross Taylor](https://en.wikipedia.org/wiki/Stuart_Ross_Taylor) is also a distinguished geologist, one who worked on the lunar samples returned by the Apollo missions.
Gimelist
CC BY-SA 3.0
2016-08-02T21:37:51.697Z
Interesting! I've actually only just changed my name to Taylor-Turner from Turner so it's all new to me :)
Ross Taylor-Turner
<geology>
If I was to tunnel straight through a mountain, what kind of rock would I find?
Ross Taylor-Turner
# If I was to tunnel straight through a mountain, what kind of rock would I find?

(Asked by: username_0 on 2016-08-02)

I'm developing a semi-realistic game involving stereotypical dwarves digging into mountainsides and carving out grand caverns for themselves, similar to those in Moria or the Lonely Mountain from Tolkien's works.

I'm attempting to research what kind of layers of rock (in layman's terms) you'd expect to find in a typical non-volcanic mountain range in say, northern Europe. So far though I'm at a loss so at this point anything would be a help!

**Tags:** geology

> **Comments:**
> **username_1**: Unrelated, but [username_0 Taylor](https://en.wikipedia.org/wiki/Stuart_Ross_Taylor) is also a distinguished geologist, one who worked on the lunar samples returned by the Apollo missions.  
> **username_0**: Interesting! I've actually only just changed my name to username_0 from Turner so it's all new to me :)  

---

## 2 answers

### Answer by username_3 on 2016-08-02. Score: 6 | Accepted answer

As Gary mentioned, it really depends on particular context for your mountain. How did it form? Is it volcanic in nature? Or maybe just old rocks being uplifted by some episode of compression.

On average, username_2's crust is pretty much granite. So chances are that you will find that inside your mountain. That wouldn't be a bad assumption. Granites form by cooling magma slowly, so most volcanic-type mountains are made of granite or something similar. For example, the Andes (below) are made of fine-grained Andesite near the surface and Diorite (Andesite's coarse-grained version, which is similar to Granite, but not quite) at depth.

[![enter image description here](https://i.sstatic.net/IsSoy.jpg)](https://i.sstatic.net/IsSoy.jpg)

In the case of cooling magma to form rocks, the slower the cooling, the larger the crystals will be. So rocks that cooled near the surface, will be composed of tiny crystals while rocks that cooled deeper will have larger crystals.

[![enter image description here](https://i.sstatic.net/hvoe6.jpg)](https://i.sstatic.net/hvoe6.jpg)

You could argue for more exotic rock types but that would imply a slightly more complex geological history (which is totally possible). For example, you could have uplifted a huge package of sedimentary rocks without any volcanism involved. Or you could have simply eroded everything around leaving large rock packages like the Venezuelan Tepuis (below).

[![enter image description here](https://i.sstatic.net/8ZTNq.jpg)](https://i.sstatic.net/8ZTNq.jpg)

In general, the rocks deep inside a mountain (or simply super old rocks) have also undergone a lot of compression, so sedimentary rocks will be unlikely as you would have converted them into metamorphic rocks, e.g. limestones would be marble, sandstones would be quartzites (like the Tepuis), shales would be slates (or schists, etc.), etc.

Similarly, metamorphic rocks that have undergone a higher degree of compressional and thermal stress (i.e. deeper in the mountain) will grow larger crystals.

[![enter image description here](https://i.sstatic.net/i72Yo.jpg)](https://i.sstatic.net/i72Yo.jpg)

Of course, like anything in geology, other complex scenarios do exist where these rules of thumb don't work. But in general, this should get you started.

Anyway, hope that helps.

> **Comments:**
> **username_0**: Exactly what I was looking for, thank you very much!  

---

### Answer by username_2 on 2016-08-02. Score: 3

It would completely depend on location. For instance, Sawtooth mountains in Idaho is a very large granite batholith so the rock in the tunnel would igneous granitic rock with varying textures and crystal sizes. You need to define a geological setting for the location first.  
- Pacific Northwest - volcanic rock, large volcanic peaks.
- BlackHills of SD - Granitic core surrounded by metamorphic sedimentary rocks and unlatered sedimentary rocks.

My recommendation is check out a couple of the Roadside Geology of .... books. These books are written in layman terms with explanations of the geology.  
See Roadside geology of Colorado ISBN:087842105X


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