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A general guide for using the Forum with some rules and tips
FMF Guide of Rocks - SEDIMENTARY ROCKS
  
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prcantos
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PostPosted: Aug 06, 2012 13:01    Post subject: FMF Guide of Rocks - SEDIMENTARY ROCKS  

I am really pleased to start this thread concerning rocks, after a similar and successful initiative at Spanish FMF Forum. I am so grateful to site admins for asking me to begin explaining what this guide consists of.

We are trying to collect photographs of rocks all around the world and as much information as possible about them: age, origin, description, composition... Rocks are closely related to minerals, as we usually find them forming rocks or growing on their surfaces and cavities. We intend to make a collective work where everybody can contribute and where expert opinions of geologists an petrologists is widely appreciated.

Photographs should show the macroscopical appearance of the specimen, though detailed pictures are usually advisable.

In order to keep the guide in order and reach and to guarantee a significant scientific level, you should proceed according to these rules:

1) If you are not sure about your rock specimen (mostly the name or the kind of rock), you should create before a new thread at "What is it? - Where is it from?" section giving the pictures and as much information as possible.

2) When the rock is properly identified, you can upload the photographs and the data in the corresponding section of FMF Rocks Guide (Igneous Rocks, Sedimentary Rocks or Metamorphic Rocks). If the rock do not fit a single group (e. g. some serpentinites, charnockites, some slates...), please choose the most accurate group in your opinion and explain it.

3) Use FMF fields at uploading photographs in this way:

*) MINERAL: write the whole name of the rock (name, varieties if known...)

*) LOCALITY: write the whole name of the location where the rocks was collected (include as many as possible: deposit, mine, geographical name, geological formation name, locality, region, country...). Please be precise at this point, your rock will be seen worldwide!

*) SIZE: in figures, or put some reference next to the specimen in the picture (a coin, a key, a pen...)

*) COMMENTS: write here the rest of the information, everything you consider to be interesting.

Of course further opinions and discussions are always welcome! Prosit!


FMF Guide of Sedimentary Rocks

Sedimentary rocks can be classified according to different criteria. A chemical classification contains these families:

[1] Siliceous and siliciclastic rocks: conglomerate, breccia, sandstone, siltstone, non-crystalline or microcrystalline forms of silica (opalo, chert, calcedonia...)

[2] Carbonate rocks: limestone, dolostone...

[3] Phosphatic rocks: phosphorus-rich rocks, e. g. phosphorite, phosphate nodules, bone beds, phosphatic mudrocks...

[4] Saline rocks: evaporites (halite, gypsum, anhidrite...)

[5] Iron-rich rocks: banded iron formations and similar.

[6] Manganese-rich rocks: nodules and layers in deep marine volcanic environments.

[7] Organich-rich rocks: varieties of coal, bituminous slates...


A genetic tipology may be:

[1] Clastic rocks: rocks containing particles which were placed in sedimentary basins, e. g. conglomerate, breccia, sandstones, lutites...

[2] Chemical sedimentary rocks: formed by inorganically precipitacion of minerals from supersaturated solutions, e. g. limestones, dolostones, evaporites...

[3] Organic sedimentary rocks: from incomplete decomposition of organic substances, e. g. coals, oil-petroleum, some bituminous rocks...


References

W. Maresch & O. Medenbach, Rocas, Barcelona (Spain) 1990.
F. Bastida, Geología, una visión moderna de las Ciencias de la Tierra (2 vols), Gijón (Spain) 2005.

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PostPosted: Aug 06, 2012 13:06    Post subject: Re: FMF Guide of Rocks - SEDIMENTARY ROCKS  

A sedimentary rock bearing fossils.


IMAG0448.jpg
 Description:
Fossiliferous limestone (bone bed)
Aust Cliff (Aust, South Gloucestershire, United Kingdom)
This upper-Triassic calcareous rock contains coprolites and bone and teeth fragments, as a kind of made-of-fossils conglomerate.
 Viewed:  15814 Time(s)

IMAG0448.jpg



IMAG0449.jpg
 Description:
Fossiliferous limestone (back side)
Aust Cliff (Aust, South Gloucestershire, United Kingdom)
Look at the black tooth in the upper part.
 Viewed:  15805 Time(s)

IMAG0449.jpg



tooth.jpg
 Description:
Detail of the tooth
Aust Cliff (Aust, South Gloucestershire, United Kingdom)
20X
 Viewed:  15821 Time(s)

tooth.jpg



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prcantos
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PostPosted: Aug 12, 2012 07:06    Post subject: Re: FMF Guide of Rocks - SEDIMENTARY ROCKS  

A glacial conglomerate (tillite).


IMAG0463.jpg
 Description:
Tillite (Lowestoft Till Glacial Conglomerate)
Thorpeness, Suffolk (United Kingdom)
Siliceous and calcareous clasts, with rounded or angular shapes and different sizes, were cemented in a marlstone matrix ca. more than half a million years ago.
 Viewed:  15725 Time(s)

IMAG0463.jpg



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PostPosted: Sep 19, 2012 11:34    Post subject: Re: FMF Guide of Rocks - SEDIMENTARY ROCKS  

Gypsum-rock from an evaporitic basin which was a Pliocen lake.


y 003.jpg
 Description:
Gypsum-rock
Salazar (Baza, Granada, Spain)
 Viewed:  15431 Time(s)

y 003.jpg



y 004.jpg
 Description:
Gypsum-rock (back)
Salazar (Baza, Granada, Spain)
 Viewed:  15432 Time(s)

y 004.jpg



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PostPosted: Sep 24, 2012 05:24    Post subject: FMF Guide of Rocks - SEDIMENTARY ROCKS / Breccia  

Per Pablo request:
prcantos wrote:
Really beautiful rock. Why don't you put the specimen and the explanations in the FMF Guide of Rocks - SEDIMENTARY ROCKS ?

I copied in this thread the Breccia that Geometerichachi published here and I also add the fine comments about it from Peter Megaw and Volkmar Stingl

In http://www.mineral-forum.com/message-board/viewtopic.php?p=25844#25844 Peter Megaw wrote:

This is a GREAT breccia...the cut face tells a wonderful story

The breccia is matrix supported with highly angular, even embayed fragments, in a layered matrix.

The matrix layering does not penetrate the fragments and in places layers appear to cut across other layers lying to their left.

Along the dark to lighter matrix zone the fragments appear to disturb/distort the layering.

The fragments get smaller to the right

overall it looks like UP is to the right.

The fragments look remarkably homogenous...but also are pitted and bleached, so I think that is a hydrothermal effect.

This looks to me like an internal cavern sediment dominated by "gossan" minerals at first, with fragments of corroded limestone dropped in, follwed by later layers of fine insoluble materials. The layers at the right appear to be more like Terra Rossa cavern fill than the dark iron-oxide layers on the left.

I think this came from a solution cavity lying below an oxidizing limestone replacement deposit of some kind. the cavity was dissolved by corrosive acid fluids derrived from oxidation of pyrite and sequentially filled with insoluble residue from the limestone and overlying orebody. occasionally chunks of altered limestone peeled off the back of the pocket and fell into the layered sediment fill

Good chance this was cut off the bottom of a nice wulfenite or mimetite specimen?



In http://www.mineral-forum.com/message-board/viewtopic.php?p=25845#25845 Volkmar Stingl wrote:

Peter, you got it! I think like you, this is a nice example of karst breccia like I have seen many before (in the Chinese karst regions, but also in the Upper Carboniferous/Early Permian karst of the Eastern Alps, and others). I like your explanation, it contains all details... (but to make it sure, you finally need the outcrop information).

Volkmar





Breccia 2.jpg
 Description:
Breccia
West US
Penny to scale
 Viewed:  15365 Time(s)

Breccia 2.jpg



Breccia 3.jpg
 Description:
Breccia
West US
Penny to scale
 Viewed:  15384 Time(s)

Breccia 3.jpg


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PostPosted: Dec 11, 2013 17:45    Post subject: Re: FMF Guide of Rocks - SEDIMENTARY ROCKS  

Siltstone is a consolidated detritic sedimentary rock with grain size between 0.002 (clays, or lutites, or pelites) and 0.063 mm. (sand, or psammites). Quartz and clays minerals are the main components, there may be many different accesories: mica, oxides, zeolites, calcite, dolomite, gypsum... It is often associated to clays, but there is a noticeable difference: siltstone has a rough touch while clays have a soft or greasy touch.


IMG_2921.JPG
 Description:
Siltstone
Huddersfield, West Yorkshire, England, United Kingdom
7'5 x 3 cm. (front) x 7 cm.
 Viewed:  11853 Time(s)

IMG_2921.JPG



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