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Ravneberget, S√łndeled, Norway- Under construction

Last Updated: 23rd Aug 2014

This article is still under construction.

Introduction



The Ravneberget quarry has been operated on and off for at least 50 years. The quarry itself has been operated to produce gravel and sand used for road construction and civil work in the neighboring area. The quarry has been operated by various owners for several decades, although not at a grand scale. The activity here is linked to the general construction activity in the area. The collectable minerals are predominantly of metasomatic and/ or hydrothermal origin, and consequently found in veins in the metagabbro host rock. It s one of the localities that rarely is the main target or an outing, but is more of a drop-in type. Every now and then these drop-ins last for many hours. 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 common sense with regards to safety.

Geology



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 different minerals found have either originated in the main rock forming sveco-norwegian orogeny, or by the later hydrothermal events.


Ravneberget overview

Ravneberget North wall

Ravneberget South Wall

Scapolite vein


Scapolite/feldspar veins



Prehnite

Prehnite is found here in a wide variety of forms, mineral associations and colors. 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. In this association, I have found crystals in two different habits. Regular prehnite-green prismatic couloums 3-4mm tall and 1mm across. Occasionally, also transparent, table formed square crystals up to 5mm on the side has been found.

Although prehnite is also found in other environments, but the mineral is most commonly found 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 colors from clear, white, gray, 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


Albite


Albite

Calcite, prehnite and albite




Hornblende veins




Actinolite

Ilmenite


Actinolite

Ilmenite

Hornblende

Sulphide veins/lenses




Sulphide vein

The sulphides are found in thin veins or small lenses. I have not seen any of these lenses wider than 10 cm. Pyrrhotite is the dominant mineral, but they also some massive pyrite and chalcopyrite, and possibly other minerals as well. Growing from host rock into the veins are normally hornblende and less frequently apatite crystals. The massive sulphides may contain well crystallized pyrite up to 3 cm.

Pyrite


elongated pyrite octahedron, front view

pyrite pyriteoedron

Pyrite octahedron



Pyrite, octahedral {111}crystal modified by {210}

elongated pyrite octahedron, front view

pyrite pyriteoedron



Pyrite octahedron

modified pyritohedron

matrix specimen w/octaedron & elongated pyriteoedron



detail 1 from matrix specimen

detail 2

detail 3


The pyrites pictured here are not large ( from 1-3cm), but all of them came from a small sulphide vein/lens not more than maximum 5cm wide. The pyrites in the sulphide veins show a wide range of crystal forms, but I have not seen any cubes, and it seems as if various octahedral and pyritohedral forms are the most common.

Calcite veins




Quartz/ Calcite veins





calcite and quartz


Prehnite / Zeolite veins

























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Comments

Beautiful specimen Revheim, more interesting.
Alessio Piccioni

Alessio Piccioni
23rd Nov 2009 9:25am

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