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A general guide for using the Forum with some rules and tips
FMF Guide of Rocks - METAMORPHIC ROCKS
  
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prcantos
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PostPosted: Aug 06, 2012 13:09    Post subject: FMF Guide of Rocks - METAMORPHIC 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 Metamorphic Rocks

Nomenclature and classification of metamorphic rocks involves textural, mineralogical and genetical criteria, as well as widely used common names. Thus a classification of metamorphites cannot be simple. Following works and concepts by Eskola (facies), Winkler (grade of metamorphism) and Miyashiro (P/T ratio and series of facies), we can use this system:

(A) Metamorphic facies in contact metamorphism (ordered by increasing grade):

[A1] Albite-epidote-hornfels facies
[A2] Hornblende-hornfels facies
[A3] Pyroxene-hornfels facies
[A4] Sanidinite facies (very rare conditions)

(B) Low and medium P/T ratio regional metamorphism:

*) Facies at very low-grade metamorphism:
[B1] Zeolite facies (laumontite or heulandite-bearing rocks)
[B2] Prehnite-pumpellyte facies (prehnite-pumpellyte-bearing rocks, metapyroclastic rocks)
*) Facies at low and medium-grade metamorphism:
[B3] Greenschist facies (slates, phyllites, chloritoid-schists, chlorite-schists, micaschists)
[B4] Amphibolite facies (epidote-amphibolites often have been considered a transitional facies or subfacies between greenschists and amphibolites)
*) Facies at high-grade metamorphism:
[B5] Granulite facies (gneisses, granulites, charnockites, migmatites)

(C) High P/T ratio regional metamorphism (ordered by grade)

[C1] Lawsonite-albite-chlorite facies
[C2] Blueschist facies (schists bearing lawsonite, riebeckite, crossite...)
[C3] Eclogite facies (jadeite-bearing rocks, eclogites)

However, sometimes may be useful a simple system that pay attention to the composition of rocks and separate some common types of metamorphites that don't fit single facies. I propose these families according to the protolith (1-7) or the main factor of metamorphism (8-9):

[1] Metacarbonates: marble in many differents compositions and varieties, except metasomatic ones.

[2] Metapelites: rocks resulting of regional metamorphisms of clays, e. g. slates, phyllites, schists, paragneisses...)

[3] Metapsammites: rocks resulting of regional metamorphism of coarse-grained clastic sediments, e. g. quartzites, metaconglomerates...

[4] Metagranitoids: products of metamorphism of acid plutonic rocks, e. g. orthogneisses, granulites...

[5] Metabasites: metamorphites whose protolith is a basic or ultrabasic igneous rock, as serpentinites, epidote-amphibolites, orthoamphibolites, eclogites...

[6] Migmatites: metamorphites where partial melting traces are detected, e. g. migmatites, anatexites, diatexites...

[7] Metapyroclastic rocks: products of (very) low-grade metamorphism of pyroclastic rocks.


[8.1] High-pressure metamorphites: blueschists, eclogites, jadeite-bearing rocks...

[8.2] Fault-rocks: cataclasites (including tectonic breccias and fault gouge), mylonites, blastomylonites, pseudotachylites...

[8.3] Impactites: shocked rocks, impact melt-rocks and breccias (including suevite), tektites...


[9.1] Contact metamorphic rocks: spotted slates, hornfels, buchites...

[9.2] Metasomatic rocks: argillisite, greisen, beresite, gumbeite, propylite, aceite, skarn, fenite, Ca/Mg-silicate marbles...


References

H. G. F. Winkler, Petrogenesis of Metamorphic Rocks, New York (USA) 1973.
W. Maresch & O. Medenbach, Rocas, Barcelona (Spain) 1990.
A. Miyashiro, Metamorphic Petrology, New York (USA) 1994.
D. Fettes & J. Desmons (ed.), Metamorphic Rocks, A Classification and Glossary of Terms, Cambridge (UK) 2011.

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PostPosted: Aug 06, 2012 13:20    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

This eclogite comes from the Tetys Ocean Floor!


IMAG0413.jpg
 Description:
Eclogite
Lugros (Sierra Nevada, Granada, Spain)
Lugros' eclogites belong to Betic Ophiolitic Association defined by E. Puga (1990). This ophiolitic complex is considered to be a set of fragments of Tethyan oceanic lithosphere in a context of obduction and regional orogenic metamorphism.
 Viewed:  29843 Time(s)

IMAG0413.jpg



Still_2012-07-04_182338_N0001.jpg
 Description:
Eclogite (detail)
Lugros (Sierra Nevada, Granada, Spain)
80X
Detailed view of the eclogite showing mineral assemblage: red garnets (almandine-pyrope), green omphacite-diopside.
 Viewed:  29854 Time(s)

Still_2012-07-04_182338_N0001.jpg



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PostPosted: Aug 12, 2012 04:25    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Another metabasite.


IMAG0461.jpg
 Description:
Serpentinite
Pujerra (Málaga, Spain)
This serpentinite comes from the northwestern edge of Ronda peridotites. It was formed by hydration of these peridotites, and it consists mainly of serpentine-group minerals.
 Viewed:  29614 Time(s)

IMAG0461.jpg



detail20X.jpg
 Description:
Serpentinite (detail)
Pujerra (Málaga, Spain)
20X
Detailed view of the previous rock, showing a flake bearing some MnO2 formations on the tectonically polished serpentine surface.
 Viewed:  29601 Time(s)

detail20X.jpg



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PostPosted: Aug 23, 2012 04:50    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

A three-colour mica schist from Sierra de Baza (Nevado-Filábride complex from Baetic Cordillera).


3colores.jpg
 Description:
Mica schist
Sierra de Baza (Granada, Spain)
Hematite (red), epidote (greenish) and graphite (grey) are the three main minerals that color this mica schist.
 Viewed:  29483 Time(s)

3colores.jpg



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PostPosted: Sep 19, 2012 11:47    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Nevado-filábride marble from Baetic Cordillera.


IMAG0369.jpg
 Description:
Stripped marble
Sierra de Baza (Granada, Spain)
 Viewed:  29263 Time(s)

IMAG0369.jpg



IMAG0367.jpg
 Description:
Fold in stripped marble
Sierra de Baza (Granada, Spain)
 Viewed:  29262 Time(s)

IMAG0367.jpg



IMAG0368.jpg
 Description:
Contact between marble (below) and metapelites (above)
Sierra de Baza (Granada, Spain)
 Viewed:  29270 Time(s)

IMAG0368.jpg



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PostPosted: Sep 21, 2012 07:41    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Sillimanite schist: a high-degree member of schists group.


IMAG0474.jpg
 Description:
Sillimanite schist
La Herradura (Granada, Spain)
Coarse-grained schist.
 Viewed:  29216 Time(s)

IMAG0474.jpg



fractfresca1.jpg
 Description:
Sillimanite schist (detail)
La Herradura (Granada, Spain)
20X
Fibrous habit white sillimanite and black biotite.
 Viewed:  29234 Time(s)

fractfresca1.jpg



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PostPosted: Jan 02, 2013 15:39    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Garnet serpentinite showing deep red pyrope crystals.


ebersd 002 copia.jpg
 Description:
Serpentinite with pyrope
Ebersdorf, Leiben, Waldviertel, Austria
9.5 x 6 cm.
Resulting of metamorphism of ultrabasic rocks, olivine transforms into serpentine minerals but garnets are preserved.
 Viewed:  28355 Time(s)

ebersd 002 copia.jpg



Sin título-1.jpg
 Description:
Pyrope crystal (detail from previous rock)
Ebersdorf, Leiben, Waldviertel, Austria
0.5 x 0.5 cm. the garnet
A light aureole borders the garnet.
 Viewed:  28362 Time(s)

Sin título-1.jpg



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PostPosted: Jan 05, 2013 15:42    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Two samples of metasomatic rocks.


Sin título-1.jpg
 Description:
Cassiterite greisen
Krupka (Graupen), Bohemia, Czech Republic
3'5 x 2 cm.
Cassiterite greisen formed by pneumatolytic metasomatism of granitoids. Black small cassiterite crystals and violet fluorite.
 Viewed:  28263 Time(s)

Sin título-1.jpg



M0248.jpg
 Description:
Cassiterite crystal on the back side of previous rock
Krupka (Graupen), Bohemia, Czech Republic
1 cm2. the base of the crystal
 Viewed:  28250 Time(s)

M0248.jpg



ox 004 copia.jpg
 Description:
Wollastonite marble
Willsboro, Essex Co., New York, USA
5'5 x 4'5 cm.
Coarse grained marble metasomatically modified: original carbonates become calcium silicate due to aqueous fluids circulation, forming a white wollastonite matrix with green diopside and red grossular.
 Viewed:  28254 Time(s)

ox 004 copia.jpg



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PostPosted: Jan 11, 2013 14:52    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Chloritoid schist.


lw 019 copia.jpg
 Description:
Chloritoid schist
Grubependity Lake, Prepolar Ural, Komi Republic, Northern Region, Russia
5x2.5 cm.
Black chloritoid porphyroblasts in a micaschist showing well-developed schistosity.
 Viewed:  28131 Time(s)

lw 019 copia.jpg



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PostPosted: Jan 28, 2013 07:08    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Staurolite micaschist from Kola.


strlt042.jpg
 Description:
Staurolite micaschist
Keyvi, Kola Peninsula, Russia
10 x 6 cm.
Staurolite twinnings in fine-grained micaschist.
 Viewed:  27872 Time(s)

strlt042.jpg



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PostPosted: Jan 28, 2013 08:31    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Wonderful photos, great information. Very helpful for a casual but a 50 year collector of rock and minerals. As I am particularly fascinated with rocks. This site in general is outstanding and has re-sparked my interested in my life long love of collecting. Thank you all.
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PostPosted: Jan 30, 2013 08:28    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Nice to meet you and your interest in rocks.
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PostPosted: Apr 24, 2013 14:50    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Tourmaline may be an accessory mineral in metapelites.


trm 008 copia.jpg
 Description:
Tourmaline-bearing micaschist
El Chive, Lubrín, Almería, Andalucía, Spain
10 x 6 cm.
 Viewed:  26638 Time(s)

trm 008 copia.jpg



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PostPosted: Dec 07, 2013 13:43    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS - eclogites  

Some eclogites.


Sin título-1.jpg
 Description:
Eclogite
Åheim, Vanylven, Møre og Romsdal, Norway
5 x 4 cm.
Red garnets (almandine-pyrope series) in a matrix of green omphacite. This is a B-type eclogite (Coleman 1965) or Group II-eclogite (Miyashiro 1994): eclogite boudins inside migmatitic gneises.
 Viewed:  23607 Time(s)

Sin título-1.jpg



60X (4).jpg
 Description:
Eclogite (detail)
Åheim, Vanylven, Møre og Romsdal, Norway
60X
Detailed view of the previous rock. Essential minerals: omphacite (green) and garnet (red). Brownish mineral may be clinozoisite, and black long crystals may be amphibole.
 Viewed:  23602 Time(s)

60X (4).jpg



IMG_2680 copia.jpg
 Description:
Eclogite
Almklovdalen, Vanylven, Møre og Romsdal, Norway
11'5 x 8 cm.
A banded eclogite wiht garnet porphyroblasts and small blue kyanite spots (center and bottom). The white layers are a mixture of quartz, jadeite, kyanite and clinozoisite. This is an A-type or Group III-C eclogite: eclogite included inside peridotites.
 Viewed:  23610 Time(s)

IMG_2680 copia.jpg



Still_2013-11-26_214312_N0004.jpg
 Description:
Eclogite (detail)
Almklovdalen, Vanylven, Møre og Romsdal, Norway
2 mm. width
Detailed view of the previous rock. Essential minerals: omphacite (green) and garnet (red). Accesories: blue kyanite, and probably golden zircons.
 Viewed:  23603 Time(s)

Still_2013-11-26_214312_N0004.jpg



IMG_2836 copia.jpg
 Description:
Eclogite
Mitchell County, North Carolina, USA
4'5 x 3 cm.
A dark eclogite poor in jadeite. The mineral assemblage at the thermal peak is omphacite (Jd27–35) + garnet (Alm48 - Prp30 Grs22) + quartz + rutile ± zoisite ± zircon ± apatite ± sulfides ± Fe-Ti oxides (cf. B. V. Miller, K. G. Stewart, D. L. Whitney, Three tectonothermal pulses recorded in eclogite and amphibolite of the Eastern Blue Ridge, Southern Appalachians, abstract at http://memoirs.gsapubs.org/content/206/701.abstract ).
 Viewed:  23597 Time(s)

IMG_2836 copia.jpg



60X.jpg
 Description:
Eclogite (detail)
Mitchell County, North Carolina, USA
60X
Detailed view of the previous rock. Grey transparent quartz grains are perceptible.
 Viewed:  23598 Time(s)

60X.jpg



IMG_2841 copia.jpg
 Description:
Eclogita
Glenelg, North West Highlands, Scotland, United Kingdom
7 x 3'5 cm.
This rocks comes from a region where evidences of ultrahigh pressure/temperature metamorphism were found. Cf. K. Sajeeva, T. Kawaib, S. Omorib, B. F. Windleyc, S. Maruyamab, P–T evolution of Glenelg eclogites, NW Scotland: Did they experience ultrahigh-pressure metamorphism?, abstract at http://www.sciencedirect.com/science/article/pii/S0024493709003892 ).
 Viewed:  23569 Time(s)

IMG_2841 copia.jpg



60X.jpg
 Description:
Eclogite (detail)
Glenelg, North West Highlands, Scotland, United Kingdom
60X
Detailed view of the previous rock.
 Viewed:  23557 Time(s)

60X.jpg



IMG_2839 copia.jpg
 Description:
Eclogite
Nordfjord, Sogn og Fjordane, Norway
7 x 5 cm.
This norwegian eclogite shows some signs of alteration after the thermal peak: garnets show chlorite ± hornblende rims, and retrograde plagioclase is described. Cf. http://www.see.leeds.ac.uk/structure/norway/nordfjord/ .
 Viewed:  23608 Time(s)

IMG_2839 copia.jpg



60X2.jpg
 Description:
Eclogite (detail)
Nordfjord, Sogn og Fjordane, Norway
60X
Detailed view of the previous rock. Dark chlorite ± amphibole rims around garnets. Blue kyanite can also be shown (not in this picture). Small golden crystals may be zircons.
 Viewed:  23613 Time(s)

60X2.jpg



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PostPosted: Dec 07, 2013 14:23    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

I will send a picture of a sample I have . I think it is in the office so may have to wait until Monday
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PostPosted: Dec 11, 2013 17:34    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

Some non-hornfelsic contact metamorphic rocks.


IMG_2917.JPG
 Description:
Cordierite schist
Cumbria, England, United Kingdom
8 x 4 cm.
Black cordierite grains in this lightly schistose rock.
 Viewed:  23293 Time(s)

IMG_2917.JPG



IMG_2911.JPG
 Description:
Chiastolite slate
Blencathra, Cumbria, England, United Kingdom
8 x 8 cm.
 Viewed:  23296 Time(s)

IMG_2911.JPG



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PostPosted: Jul 05, 2015 06:56    Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS  

A blueschist from the high-pressure metamorphic terrains at the Western Alps.

Red spessartine garnets are surrounded by blue glaucophane, silver mica and white quartz. Green crystals might be omphacite or better kyanite (read the explanation at the 4th & 5th picture).



IMG_4732 copia.jpg
 Mineral: Spessartine glaucophane schist
 Locality:
Bagnes Valley, Wallis (Valais), Switzerland
 Dimensions: 12 x 16 cm.
 Description:
An altered side of the rock.
 Viewed:  11592 Time(s)

IMG_4732 copia.jpg



IMG_4743 copia.jpg
 Mineral: Spessartine glaucophane schist
 Locality:
Bagnes Valley, Wallis (Valais), Switzerland
 Dimensions: FOV 4.5 cm.
 Description:
Lateral view of the specimen showing schistosity and flow structure.
 Viewed:  11598 Time(s)

IMG_4743 copia.jpg



IMG_4736 copia.jpg
 Mineral: Spessartine glaucophane schist
 Locality:
Bagnes Valley, Wallis (Valais), Switzerland
 Dimensions: 20 x 16 cm.
 Description:
A fresh polished surface.
 Viewed:  11593 Time(s)

IMG_4736 copia.jpg



IMG_4738 copia.jpg
 Mineral: Spessartine glaucophane schist
 Locality:
Bagnes Valley, Wallis (Valais), Switzerland
 Dimensions: FOV 4 cm.
 Description:
Detailed view of the polished surface.

The main green crystal shows a 75º cleavage according to (100) and (010) faces of the kyanite, so we should consider it is kyanite better than omphacite (I haven't got an analysis).
 Viewed:  11593 Time(s)

IMG_4738 copia.jpg



IMG_4739 copia.jpg
 Mineral: Spessartine glaucophane schist
 Locality:
Bagnes Valley, Wallis (Valais), Switzerland
 Dimensions: FOV 5 cm.
 Description:
Another partial view of the polished surface with an interesting detail.

Next to the green crystals you can see a white mineral showing evident cleavage, so it can't be quartz (quartz appears here as a massive frame of garnets). It might be albite (a mineral possible in this blueschist facies). Albite can hardly ever coexist with omphacite according to the metamorphic reaction

albite < --- > jadeite + quartz

As jadeite is an essential component of omphacite, the presence of albite discards the omphacite in a high degree. Anyway omphacite can coexist sometimes wiht retrograde albite to some extent.
 Viewed:  11607 Time(s)

IMG_4739 copia.jpg



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Pablo Rodríguez Cantos
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