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prcantos
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Posted: Aug 06, 2012 13:09 Post subject: FMF Guide of Rocks - METAMORPHIC ROCKS |
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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.
_________________ Pablo Rodríguez Cantos
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prcantos
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Posted: Aug 06, 2012 13:20 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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This eclogite comes from the Tetys Ocean Floor!
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. |
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Eclogite (detail) Lugros (Sierra Nevada, Granada, Spain) 80X Detailed view of the eclogite showing mineral assemblage: red garnets (almandine-pyrope), green omphacite-diopside. |
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91389 Time(s) |
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prcantos
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Posted: Aug 12, 2012 04:25 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Another metabasite.
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. |
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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. |
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91134 Time(s) |
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prcantos
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Posted: Aug 23, 2012 04:50 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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A three-colour mica schist from Sierra de Baza (Nevado-Filábride complex from Baetic Cordillera).
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. |
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91102 Time(s) |
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prcantos
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Posted: Sep 19, 2012 11:47 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Nevado-filábride marble from Baetic Cordillera.
Description: |
Stripped marble Sierra de Baza (Granada, Spain) |
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90833 Time(s) |
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Fold in stripped marble Sierra de Baza (Granada, Spain) |
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90857 Time(s) |
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Contact between marble (below) and metapelites (above) Sierra de Baza (Granada, Spain) |
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90733 Time(s) |
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prcantos
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Posted: Sep 21, 2012 07:41 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Sillimanite schist: a high-degree member of schists group.
Description: |
Sillimanite schist La Herradura (Granada, Spain) Coarse-grained schist. |
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90820 Time(s) |
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Sillimanite schist (detail) La Herradura (Granada, Spain) 20X Fibrous habit white sillimanite and black biotite. |
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90767 Time(s) |
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prcantos
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Posted: Jan 02, 2013 15:39 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Garnet serpentinite showing deep red pyrope crystals.
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. |
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89847 Time(s) |
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Pyrope crystal (detail from previous rock) Ebersdorf, Leiben, Waldviertel, Austria 0.5 x 0.5 cm. the garnet A light aureole borders the garnet. |
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89965 Time(s) |
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prcantos
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Posted: Jan 05, 2013 15:42 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Two samples of metasomatic rocks.
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. |
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89835 Time(s) |
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Cassiterite crystal on the back side of previous rock Krupka (Graupen), Bohemia, Czech Republic 1 cm2. the base of the crystal |
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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. |
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89799 Time(s) |
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prcantos
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Posted: Jan 11, 2013 14:52 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Chloritoid schist.
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. |
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89597 Time(s) |
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prcantos
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Posted: Jan 28, 2013 07:08 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Staurolite micaschist from Kola.
Description: |
Staurolite micaschist Keyvi, Kola Peninsula, Russia 10 x 6 cm. Staurolite twinnings in fine-grained micaschist. |
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89519 Time(s) |
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Larry Laskowski
Joined: 17 Jan 2013
Posts: 9
Location: James Island, SC
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Posted: Jan 28, 2013 08:31 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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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.
_________________ Larry Laskowski |
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prcantos
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Posted: Jan 30, 2013 08:28 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Nice to meet you and your interest in rocks.
_________________ Pablo Rodríguez Cantos
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prcantos
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Posted: Apr 24, 2013 14:50 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Tourmaline may be an accessory mineral in metapelites.
Description: |
Tourmaline-bearing micaschist El Chive, Lubrín, Almería, Andalucía, Spain 10 x 6 cm. |
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88326 Time(s) |
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prcantos
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Posted: Dec 07, 2013 13:43 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS - eclogites |
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Some eclogites.
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. |
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85195 Time(s) |
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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. |
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85078 Time(s) |
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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. |
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85134 Time(s) |
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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. |
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85116 Time(s) |
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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 ). |
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85084 Time(s) |
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Eclogite (detail) Mitchell County, North Carolina, USA 60X Detailed view of the previous rock. Grey transparent quartz grains are perceptible. |
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85084 Time(s) |
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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 ). |
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84953 Time(s) |
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Eclogite (detail) Glenelg, North West Highlands, Scotland, United Kingdom 60X Detailed view of the previous rock. |
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84989 Time(s) |
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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/ . |
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85184 Time(s) |
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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. |
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85084 Time(s) |
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Mark Ost
Joined: 18 Mar 2013
Posts: 516
Location: Virginia Beach
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Posted: Dec 07, 2013 14:23 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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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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prcantos
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Posted: Dec 11, 2013 17:34 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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Some non-hornfelsic contact metamorphic rocks.
Description: |
Cordierite schist Cumbria, England, United Kingdom 8 x 4 cm. Black cordierite grains in this lightly schistose rock. |
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85266 Time(s) |
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Description: |
Chiastolite slate Blencathra, Cumbria, England, United Kingdom 8 x 8 cm. |
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84758 Time(s) |
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prcantos
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Posted: Jul 05, 2015 06:56 Post subject: Re: FMF Guide of Rocks - METAMORPHIC ROCKS |
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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).
Mineral: | Spessartine glaucophane schist |
Locality: | Bagnes Valley, Wallis (Valais), Switzerland | |
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Dimensions: | 12 x 16 cm. |
Description: |
An altered side of the rock. |
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73035 Time(s) |
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Mineral: | Spessartine glaucophane schist |
Locality: | Bagnes Valley, Wallis (Valais), Switzerland | |
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Dimensions: | FOV 4.5 cm. |
Description: |
Lateral view of the specimen showing schistosity and flow structure. |
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72969 Time(s) |
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Mineral: | Spessartine glaucophane schist |
Locality: | Bagnes Valley, Wallis (Valais), Switzerland | |
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Dimensions: | 20 x 16 cm. |
Description: |
A fresh polished surface. |
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73242 Time(s) |
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Mineral: | Spessartine glaucophane schist |
Locality: | Bagnes Valley, Wallis (Valais), Switzerland | |
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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). |
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73043 Time(s) |
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Mineral: | Spessartine glaucophane schist |
Locality: | Bagnes Valley, Wallis (Valais), Switzerland | |
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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. |
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73037 Time(s) |
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