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Layered rock - does it have a specific name?


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Does this type of layering in the rock have a specific name?  Not the rock itself particularly (though that would be helpful) but I was wondering if the layering had a specific name.

 

Taken at the Cascade Saddle, Mount Aspiring National Park, Southern Alps, New Zealand.  Mount Edward in the background.

 

B65YK2.jpg

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It is impossible to definitively identify a rock type with a photo like this as it could be any one of several rock types: shale (laminated mudstone), slate, schist, something volcanic. However, I would guess it is a schist from a quick internet search as there are schists documented in this area. A schist is a metamorphosed shale or mudstone. But it is impossible to say from the picture. I would need to examine the rock under a microscope to be really sure what it is without reading a geological description of the specific area. 

 

In Britain and Ireland there are now detailed geological maps, often with descriptions, available online so if you know the grid reference it is often possible to identify the rock. There may be something similar for New Zealand. 

Edited by MDM
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They may not be bedding planes or strata at all and that cannot be assumed. They could be metamorphic cleavage which will generally have a different orientation to the bedding unless the metamorphic compression direction is perpendicular to the bedding which is rare.

 

It would be necessary to see the rock in hand specimen at least to say as well as taking the local and regional geology into account. If it is a schist, then it will probably have shiny crystals flattened along the cleavage. If is a slate the crystals may be too small to see with the naked eye. 

 

 

 

 

Edited by MDM
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9 minutes ago, meanderingemu said:

in addition to above, I would also include "striation" in KW 

 

They are not striations. The term glacial striations (or striae) refers to lines on rocks that have been scraped under a glacier by rocks carried along by the glacier. You would find these on the flat surface of the rock and they don't look anything like this. You can also find striations when rocks scrape along each other on a fault plane. It generally refers to a physical scraping process. 

 

Edited by MDM
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2 minutes ago, MDM said:

 

They are not striations. The term glacial striations (or striae) refers to lines on rocks that have been scraped under a glacier by rocks carried along by the glacier. You would find these on the flat surface of the rock and they don't look anything like this. I do know what I am talking about. I am a former professional geologist. 

 

 

i guess i misjudge the background to be a glacier on my phone.  thanks

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3 minutes ago, meanderingemu said:

 

 

i guess i misjudge the background to be a glacier on my phone.  thanks

 

There are glaciers there but these are not glacial striations. 

 

EDIT: These are planar two D structures as they go through the rock. Glacial striations are linear 1 dimensional structures which affect only the surface.

Edited by MDM
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Rather than getting intense over how we can't identify the rock without a magnifying glass I would go ahead and keyword what appears to be in the picture. 

 

Layers, strata, sediment, bedding planes, geology, geological, formation, rock, rocks, - are tags I would use. I'd go with these being rocks that started off as sedimentary and were metamorphosed through the pressure of fold mountain building. 

 

Striations are surface scratches created by moving ice - so not appropriate here because we only have a side view.

 

 

Edited by geogphotos
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11 minutes ago, Mr Standfast said:

So what would be safe/appropriate for a text book?

 

Just curious.

What geog said leaving out the rock type, presumably. With a precise location so that the buyer can relate it to a geological map as MDM says.

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19 minutes ago, Mr Standfast said:

So what would be safe/appropriate for a text book?

 

Just curious.

 

A lot of geological text books use pictures from the geologists who wrote them and have studied the rocks. Even way back a lot of geologists carried SLRs and would photograph rocks, often with a hammer or something else for scale. The pictures would not usually be the most aesthetically beautiful but they would be accurate. Accuracy is the key thing so if using stock photos it is very important that they are captioned correctly if used for educational purposes. Many types of geological features lend themselves to easy identification and with modern internet maps it can be easy to check up what rock types are exposed in a location.

 

However, that is not the case here. In this case, using terms such as bedding and strata could be entirely misleading as these planar structures could be of metamorphic origin. To explain, beds, strata etc are depositional so formed when the sediment was actually laid down. These sediments eventually form rocks, typically by gravitational compression as more sediment is laid down on top giving consolidated bedded rocks. Millions or even billions of years later, large scale tectonic movements (typically lateral that is from the side, not gravitational) can completely destroy the original bedding giving what is called cleavage formed by compression and recrystallisation of the minerals in the rock to form slate or schist. This may well be what has happened here given that there are schists in this area. Calling it bedding may be entirely misleading. 

 

EDIT: This is basic 1st or 2nd year geology, the sort of thing you learn on one of your first mapping trips as a geology student. Bedding and cleavage are entirely different and the differences are extremely important. It is not simple pedantry.

Edited by MDM
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Well, I didn't expect it would be such a minefield!  Maybe I'll just stick with 'layered rock'.

 

Thanks for all the comments - much appreciated.

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10 minutes ago, spacecadet said:

What geog said leaving out the rock type, presumably. With a precise location so that the buyer can relate it to a geological map as MDM says.

 

As a short summary, I don't think anyone writing a reputable text book would include a stock picture without checking in detail what is was. 

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6 minutes ago, Vincent Lowe said:

Well, I didn't expect it would be such a minefield!  Maybe I'll just stick with 'layered rock'.

 

Thanks for all the comments - much appreciated.

 

I have many happy memories of geological field trips arguing (normally rationally and politely if sometimes heatedly) about geological features. It is a part of the whole process and entirely normal. The one thing you would never do is say that will do. So that was mentally stimulating thanks. 

Edited by MDM
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I can quite easily imagine seeing a picture like this in a textbook with an activity for students to create hypotheses trying to explain the landscape. And then - the important part of the enquiry - considering what needs to be known, and how to go about finding out - how to challenge alternative hypotheses and evaluate evidence. 

 

Textbooks these days do not simply impart knowledge to a passive learner. 

 

Though to be honest I don't think that this picture would be the one for a textbook - more suitable for a travel feature or brochure. 

Edited by geogphotos
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1 hour ago, geogphotos said:

Though to be honest I don't think that this picture would be the one for a textbook - more suitable for a travel feature or brochure. 

 

It's been on Alamy since 2008 and not sold for any of those - or anything else for that matter!  I've had three sales from that same day though.  Total sales from that New Zealand trip have at least paid the airfare.

 

I've been making constructive use of lockdown by reviewing my keywords from way-back.  It's been a very useful exercise - I've learned a lot about keywording over the years and some of my early efforts now seem downright cringe-worthy...🥴

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11 minutes ago, wiskerke said:

Would some more images from the area be of help?

https://goo.gl/maps/3jxL5citXRaerQXWA

https://goo.gl/maps/nkYEg6ijuGR9txBu7

Not been up there btw. Looks like a great walk. (But I think it's not a Great Walk, is it?)

 

wim


Definitely a lot of metamorphic rock with very well developed cleavage (schist most likely) on the ground in those pictures. So it is a good bet that Vincents’s rock might be similar but that is not scientifically rigid. As I mentioned in my first post, there are schists in the area. 

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15 minutes ago, wiskerke said:

Would some more images from the area be of help?

https://goo.gl/maps/3jxL5citXRaerQXWA

https://goo.gl/maps/nkYEg6ijuGR9txBu7

Not been up there btw. Looks like a great walk. (But I think it's not a Great Walk, is it?)

 

wim

 

Thanks Wim.  It's a side trip from the Dart hut off the Rees-Dart track - definitely the best trek of the holiday.  Certainly a Great Walk as far as I'm concerned. 

 

The view of Mount Edward heading down off the Rees-Dart col is my favourite shot from the whole two months we spent in NZ.  I have a large print of it on my wall.  The Cascade Saddle route goes off to the right from the valley bottom.  The Dart Hut is just around the corner on the left.

 

mount-edward-from-snowy-creek-rees-dart-

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