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Ravneberget, S√łndeled, Norway

Last Updated: 15th Oct 2010

I have updated this article with a more thorough description of the geological environment, some photos of the quarry, and I have added a description and a few photos of the prehnite found here. The plan is to gradually extend the article to contain all the minerals that I know from this location.

The Ravneberget quarry is located in the Bamble sector, one of many orogene belts on the Precambrian Baltic shields. The onshore part of the Bamble sector is 20-30km wide and approximate 150 km long along the coast from Kristiansand North-East to Porsgrunn.

The Bamble sector rocks are highly metamorphosed, granulite facies near the coast and grading towards amphibolite facies further inland. The rocks are dominated by orthogneiss ( gneiss with an igneous origin), amphibolites and metasedimentary rocks, which towards the end of the orogeny was penetrated by various igneous rocks ( gabbroid rocks, tonalities, granites).

The Ravneberget quarry is located in a metagabbro, where the original pyroxene/feldspar composition now has become an amphibole/scapolite rock. The metamorphosis is believed to be caused by chlorine and phosphorous gases originated from a gabbroid magma, thus altering feldspar into scapolite and at the same time forming apatite. Most of the mineralization has however originated through much later hydrothermal activities, and studies near Blengsvann some 60km to the southwest suggest retrograde conditions at about 300 deg C and 1-2kbar.

The quarry itself has been operated to produce gravel and sand used for road construction and civil work throughout the area. The quarry has been operated by various owners for several decades, although not at a grand scale. The different minerals found have either originated in the main rock forming sveco-norwegian orogeny, or by the later hydrothermal events. Collecting at the locality is officially not permitted, but normally the quarry operators have tolerated collectors as long as they have behaved sensibly, meaning not disrupting work, staying away from machinery and obeying normal safety rules.


Ravneberget overview

Ravneberget North wall

Ravneberget South Wall

Scapolite vein






Pyrite



Sulphide vein
The pyrites pictured here are not large ( from 1-3cm), but all of them came from a small sulphide vein/lens in the metgabbro host rock in the Ravneberget quarry. The vein was not more than maximum 5cm wide, and sitting in a very hard metagabbro host rock. It seems ti have formed at the original rock forming Sveco-Norwegian event, but pyrite is also known as a hydrothermal mineral from this location.

The small sulphide lens/vein consisted primarily pyrrhotite, but also some massive pyrite and chalcopyrite, and possibly other minerals as well. It was not the assive minerals that caught my attention, but the well crystallized pyrites embedded in the pyrrhotite. I found a great number of different crystal shapes of pyrite within a very small area.

The photo to the left shows a similar sulphide vein in the rock. This vein had massive pyrite, pyrrothite and chalkopyrite surronding the hornblende crystals. The pyrite crystals pictured below originated from a very similar vein.









elongated pyrite octaedron, front view

pyrite pyriteoedron

Pyrite octaedron



modified pyrite octaedron

modified pyriteoedron

matrix specimen w/octaedron & elongated pyriteoedron




detail 1 from matrix specimen

detail 2

detail 3




Prehnite

Prehnite is found here in a wide variety of forms, mineral associations and colours, bua they are all of hydrothermal origin. Normally, the prehnite is found in crusts and botryoidal masses, but individual crystals can sometimes be recognized. The individual crystals are never huge, rarely more than a couple of mm. I have found crystals in three different habits. Regular prehnite-green prismatic couloums 3-4mm tall and 1mm across in cavities in scapolite veins. Occationally, in this this environment, also transparent, table formed square crystals up to 5mm on the side has been found. I have also found prehnite as small flat disks in thin veins in the rock with laumontite.

Botryoidal masses can either be found as thin veins in the host rock, in voids between hornblende crystals but more frequently in cavities in the scapolite veins. The prehnite layers are never thick (rarely more than 1 cm) but the cavities can be quite large. Cavity systems in scapolite lined with prehnite can be several metres. The prehnite itself can be found in a wide variety of colours from colourless, white, cray, to tones of ranging lemon to golden to almost brown, and variuos shades of green. The best coloured specimens I have seen has been with a saturated apple green ( read granny smith) in a single cavity that gave several specimens. The largest ones more than 10 cm.



Honey coloured prehnite

Transparent prehnite

greenish prehnite

Yellow transparent prehnite







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Comments

Beautiful specimen Revheim, more interesting.
Alessio Piccioni

Alessio Piccioni
23rd Nov 2009 9:25am

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