Alnö alcaline area.


DESCRIPTION

Alnö lies at the coast east of Sundsvall, Medelpad, Sweden. The alcaline area consists of a number of intrusions and dykes in an area covering over .... km.

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tobedone

There is a very interesting quarry north of Sundsvall right beside the E4. It is called Färsta.

GEOLOGY

The geology of the Alnö area is very interesting. It is one of a very few areas in the world with a alcaline volcanic area. It's chemistry is very different from the ordinary granitic rock in the area, resulting ina number of different minerals.

VISITS

Since the E4 road is passing right through this area I stop every time I drive to or from the southern of Sweden. One of the most visible signs of the vulcanic origin of the area is the vein at Bergfors at the side of the E4.

Mineral assemblage

Mineral assemblage Chacopyrite, Quartz (morion), Calcite, Aegirine, Baryte, Wollastonite, Knopite.
Rocks : Borengite, (+ many more, about 100 different)

Chalcopyrite

Chacopyrite on calcite. Sadly all crystals are gone. The only trace left is a crystal side, showing striations.
The calcite vein is in a groundmass of "berforsite", one of many different rock types found around Alnön.
Collected in Bergfors 1997.
(300 dpi, 800x600, k)
Chalcopyrite

Chacopyrite crystal on calcite. This is a big crystal (6mm). The top of it seems to have been out in the harsh environment, since it is gray and rounded. The sides is on the other hand shiny and shows heavy twinning and striations.
The calcite vein is in a groundmass of "berforsite", one of many different rock types found around Alnön.
Collected in Bergfors 1997.
(300 dpi, 800x600, k)
Knopite

This is something I'm very unsure of. I have identified it as knopite due to it's perfect cube crystal form, but it could also be bixbyite or loparite. You can see one crystal to the right in the picture.
From the Söråker intrusion, as a gift from Karin 1997.
(300 dpi, 800x600, k)
Calcite

A calcite vein from Bergfors. A very common sight there.
Collected 1995
(300 dpi, 800x600, k)
Calcite

Calcite crystals from a crevice. Crystal size up to 1 cm.
From the amphitheatre in Bergfors.
Collected in 1997
(200 dpi, 800x600, k)
Aegirine

Aegirine from a locality on the Alnö island.
As a gift from Jorge Alves in 1998
(300 dpi, 800x600, k)
Baryte

Massive baryte from the Alnö island.
Bought from Britta and Allan Bäckman, Västerås in 1998.
(300 dpi, 800x600, k)
Cancrinite

Yellow cancrinite from Alnön.
As a gift from Jorge Alves, 1998.
(300 dpi, 800x600, k)
Borengite

A nice sample of borengite from Alnön.
As a gift from Jan Thelin.
(Size 5x3x4 cm)

If you have some questions, suggestions or comments you are welcome to write me a line or two.
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axelsson@acc.umu.se