Questions tagged [petrology]

Petrology is the study of rocks and the processes that lead to their formation and alteration.

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1answer
680 views

Does flow banding only occur in silicic rocks?

I made a video about what I learnt in my A Level Geology course so far, about igneous rocks. One thing I mentioned was that flow banding is mostly only found in silicic rocks (and so mostly rhyolite) ...
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2answers
174 views

Relative dating of granite pluton

In selecting a sample for age-dating of a granite pluton, which site is a better site to collect a sample from, the centre, top or side? Why was this site a better choice? Which dating method would ...
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1answer
42 views

Why does the color of this hillside rock vary?

Below is a roadcut in central Marin County, California, in an area maps show to have Franciscan melange. I assume this is graywacke, but as you can see it varies from gray on the sides to a buff ...
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0answers
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Lithologic and hydrostratigraphic logs for the Deccan volcanic province, India

I need data on depth/thickness of of different lithologic units under Deccan Volcanic Province in MP, Maharashtra and Gujarat. For this if anyone can help in providing help in obtaining well log data ...
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2answers
923 views

How to learn the different types of rock

I would like to be able to point to a piece of rock and say that is rock type such and such. I have tried learning but it literally seems like an endless list of types and sub types and the pictures ...
8
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1answer
73 views

Identifying serpentinite reworked during high-T metamorphism

What kind of mineralogy results when a serpentinite is reworked during high-T or UHT metamorphism? I am envisaging a possible scenario where an obducted ophiolite terrane is buried and metamorphised ...
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1answer
642 views

What is the natural replenishment rate of oil? [duplicate]

What is the natural replenishment rate of oil? Are extinction events connected with higher production?
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2answers
928 views

What processes produced the basalt columns of the Giant's Causeway?

The Giant's Causeway is, according to the Wikipedia page was formed during during the Paleogene Period, Antrim was subject to intense volcanic activity, when highly fluid molten basalt intruded ...
10
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2answers
206 views

What is the geothermal potential of a volcano?

If there were lots of geothermal plants—even mobile ones—near a volcano, how much power could this provide? Could the sapping of some of the heat energy make the volcano less likely to erupt?
7
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2answers
379 views

Acidity of rock

I read that the acidic character, or, better, persilicic character of a rock is determined by a content of more than $65\%\ \ce{SiO_2}$. A rock is defined, by the texts available to me, as ...
10
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1answer
126 views

What's the partition coefficient (D) of Nb for apatite?

Was there any experimental study that determined $D$ for apatite and silicate liquid? The GERM Kd database only lists one study with carbonatite liquid, but that's not what I'm looking for.
11
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1answer
196 views

When did/will peak conventional oil happen?

Global oil reserves are, for practical purposes, limited. We're using them at a rate far exceeding the rate of deposition. At some point, we will have to spend more energy to extract remaining ...
13
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1answer
29k views

What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?

There are two groups of elements that are frequently mentioned when discussing incompatible trace elements. They are the high field strength elements (HFS or HFSE) and the large ion lithophile ...
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1answer
268 views

Why would magma have high amounts of nickel and chromium?

I am doing a research project on Mount Lamington and through my research I have found that its magma has unusually high amounts of chronium and nickel. What would cause this to happen? Is there ...
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How can I find a large petrology dataset?

I need a large dataset of the oxide components of peridotitic rocks and their manual classification for a project of mine. The only one that I managed to find was from the EarthChem database and it is ...
10
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1answer
7k views

How do you use the streckeisen (QAPF) classification ternary diagram to identify igneous rocks based on chemical rock composition?

I have been given the following diagrams: and and a database that is structured like this: ...
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1answer
2k views

How are spherulitic structures formed in basalt rock?

After having studied the thin sections of basalt under the microscope, I have come across many spherulitic structures occurring in clusters. How can this happen? Is it due to devitrification or is ...
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3answers
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Where can obsidian be found?

Where is obsidian found? Is it typically found on the surface or underground? If underground, how far under (meters or feet would be perfect)? Also, is it found everywhere on Earth, or just in areas ...
11
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2answers
1k views

Why are alkali basalts found at rifting centres and on top of 'plumes', whereas MORBs are generally tholeiitic?

So I was essentially wondering why it was that the basalts on top of 'plumes' at 'hotspots' (sometimes called OIBs, ocean island basalts) and at continental rifting centres are enriched in alkaline ...
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5answers
24k views

Why do gold deposits form only in certain areas of the earth?

In the map above you can find that most elements are spread evenly throughout Earth's crust and that they are available all around the Earth. However, gold can only be found in certain areas of the ...
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1answer
230 views

How are the patterns in solid rock born

I took this photo on my vacation in Finland showing white stripes in the rock going different ways. How are these patterns born?
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1answer
3k views

Is there such a thing as a “basalt dike”?

I've always understood that basalt is an extrusive rock (formed by eruption), and dikes are intrusions (no eruption), so I would have thought that a dike could not be composed of basalt rock. It's ...
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3answers
4k views

When can taste be used to help identify rocks?

Taste can be used to distinguish halite (ordinary salt) from sylvite (which has some bitterness) and siltstone from mudstone (the latter has a creamy texture while the grains of the former can be felt)...
16
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2answers
57k views

Are the processes of the rock cycle currently in dynamic equilibrium?

The standard representation of the rock cycle usually looks like this: Does each stage of the rock cycle currently balance? That is, are the various processes in dynamic equilibrium, so that the ...
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2answers
2k views

Why does a subduction zone produce a serpentinization diapir rather than volcanism?

The classic Troodos Ophiolite in Cyprus has been uplifted by a 'serpentinization event'. Upper mantle (peridotite) has been serpentinized creating a buoyant diapir. This has uplifted the ocean crust ...
17
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1answer
18k views

What are the differences between geology, petrology, and lithology?

What differences are there between geology, petrology, and lithology? If I were to get into any of those fields, what exactly would I be studying? Also, are petrology and lithology just branches of ...
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3answers
8k views

Why do felsic materials have lower melting points than mafic?

It is clear from Bowen's reaction series that more felsic minerals have lower melting points than mafic minerals. As far as I know, the same is true of quenched glasses. Felsics have a higher degree ...

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