prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
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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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| Viewed: |
86514 Time(s) |
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| Description: |
Chiastolite slate
Blencathra, Cumbria, England, United Kingdom
8 x 8 cm. |
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| Viewed: |
85989 Time(s) |
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_________________
Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
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prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
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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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| Viewed: |
74271 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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| Viewed: |
74181 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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| Viewed: |
74465 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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| Viewed: |
74281 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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| Viewed: |
74271 Time(s) |
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_________________
Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
|
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