Determine which rock was formed from a volcanic eruption

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Discussion Overview

The discussion revolves around identifying which of three pictured rocks is most likely formed from a volcanic eruption. The scope includes homework-related inquiry and classification of igneous rocks based on visual characteristics.

Discussion Character

  • Homework-related
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant suggests that the third rock appears mafic and has fine grains, indicating it may be from a volcanic eruption.
  • Another participant points out that the first rock is labeled "volcanic rock" and the third as "basalt," implying these labels could be significant clues.
  • A different participant expresses uncertainty about the classification, noting that basalt and andesite are both volcanic rocks and suggesting that the first rock may be more felsic and coarse, possibly indicating an intrusive origin.
  • One participant mentions that the first image may represent a phreato-magmatic explosion rather than a typical eruption, referencing the context of the image and the presence of basalt fragments.
  • Another participant identifies the second image as andesite based on its usage in multiple Wikipedia pages as an example of that rock type.
  • The third rock is identified as basalt by a participant, supported by similar reasoning as the second rock.
  • One participant expresses frustration over the lack of provided examples in the homework question, suggesting it would be clearer if different rock types were presented for comparison.

Areas of Agreement / Disagreement

Participants express differing views on which rock is most likely formed from a volcanic eruption, with no consensus reached. There are multiple competing interpretations of the images and their classifications.

Contextual Notes

Participants note the absence of specific examples in the homework question, which may affect the clarity of the task. There is also mention of the potential for misinterpretation based on the visual characteristics of the rocks.

krbs
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Homework Statement


Identify which rock pictured was most likely the result of a volcanic eruption. No info is provided besides the following pictures which I managed to find on the internet:

https://commons.wikimedia.org/wiki/File:Volcanic_rock_from_Unzen.jpg
https://commons.wikimedia.org/wiki/File:Museo_de_La_Plata_-_Andesita.jpg
https://commons.wikimedia.org/wiki/File:Olivine_basalt.jpg

Homework Equations


N/A

The Attempt at a Solution



Just based on the pictures I guessed that the third rock is from a volcanic eruption because it appears mafic and has fine grains in its matrix which are both indicative of a high cooling temperature.
 
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Well the first one it title'd "volcanic rock" and the third one is titled "basalt" ... which may be a clue :)
If this is a long-answer, then you should probably cite the source of your assertions. If you start by writing down the signs that a rock is from a volcanic eruption, then compare, you'll have a stronger argument.
 
Simon Bridge said:
Well the first one it title'd "volcanic rock" and the third one is titled "basalt" ... which may be a clue :)
If this is a long-answer, then you should probably cite the source of your assertions. If you start by writing down the signs that a rock is from a volcanic eruption, then compare, you'll have a stronger argument.
It may be! But I'm not sure because basalt and andesite are also volcanic rocks. I didn't go with the one titled volcanic because it appears more felsic and coarse (ie, intrusive). It's a short answer and not worth many marks, but it's bugging me that I don't know! Maybe if I explain my choices as you said it'll work out. Thank you for your feedback~
 
The context where the 1st image appears suggests it is a result of phreato-magmatic explosion rather than an eruption itself. The rock fragments (and caption indicating some of the fragments are basalt) seem to support this.
The second one is used in three wikipedia pages as an example of andesite - so it is almost certainly a photo of andesite.
You can google the formation of andesite.
The third is, for similar reasons, basalt.
(If you scroll down you can see which pages the pic is used in - and, if needed, get those pages translated for context.)
 
Ok, got it. Thank you!
 
krbs said:

Homework Statement


Identify which rock pictured was most likely the result of a volcanic eruption. No info is provided besides the following pictures which I managed to find on the internet:

how can they ask you to identify them if they don't give you examples ... seems rather silly
you must have missed something or the Q is just totally screwball

they should have shown you 3 rock types, say igneous, metamorphic and sedimentary and then asked for your choice and reasoning

Yes you went and picked your own 3 eruptive volcanic rock types

Dave
 

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