The Umeå area.

DESCRIPTION

Because I'm living here I look at stones whenever there is a construction site or fresh rocks around here.

GEOLOGY

The geology of Umeå is relatively simple. It is situated in an area dominated by migmatite (veined gneiss, derived from the phyllite series). There are some windows in the gneiss showing even grained revsund granite, sometimes with remnants of schist.
There is a small area of porphyrite south of Stöcke.
In the area there exists some small pegmatites. One pegmatite is located at the road cutting just east of Bergöbron, west of Obbola.
A common ingredience of the gneiss is cordierite and it could be found in many parts of the area contains. For example Sävar and Holmsund.

LITTERATURE

SGU ser Ca 37 : Beskrivning till berggrundskarta över Västerbottens län.
SGU ser Ai 37 : Flygmagnetiska kartan 20K Umeå NV
SGU ser Ak 5, del 1, jordarter. : Kvartärgeologiska kartan 20K Umeå, 20L Holmön.
Somewhere I got a map over the bedrock also ...

Mineral assemblage

Almandine, Andalusite, Cordierite.

Almandine
Small almandine garnets from a quarry near the E4 a couple of km south of Umeå.
As a gift from Jorg Alves, 1998.
(300 dpi, 800x600, k)

Andalusite
Andalusite crystal in pegmatitic material. The origin of this sample are not shure. It could be outside Umeå, but probably from the quarry at Kåddis.
I found it in rocks layd out to protect a bicycle road down the river.
Collected 1996.
(300 dpi, 800x600, k)

Andalusite
After have heard from one of the more experienced rockhounds here in Umeå that it probably was a crushed garnet, I decided to see what's hiding inside so I chopped off the lower part of the stone. At least it wasn't a garnet. It shows two cleavage planes along the crystal in about 90 degrees, and a square cross section.
I still think it's andalusite!
It also shows a strong flourescens in green.
Collected 1996.
(300 dpi, 800x600, k)

Cordierite
Blåbärsbacken consists mostly of gneiss. Where the veins of quartz and feldspar in the gneiss is wider it is possible to find fresh clear and deep purple cordierite. This is one such piece.
From Blåbärsbacken, Holmsund.
Collected in 2001.
Size : 4x3x3 cm.

Cordierite
This is opaque cordierite from the biggest quartz - feldspar vein at Blåbärsbacken, Holmsund. The vein had been blown up into large boulders, up to 200 kg, with the vein running straight through them. It was up to 30 cm wide and contained light blue to black, opaque, cordierite crystals.
The cordierite didn't show any crystal faces.
From Blåbärsbacken, Holmsund.
Collected in 2001.
Size : 6x5x3 cm.

Unknown mineral
Unknown crystal in quartz. Most likely a pyroxene crystal.
I'm not shure of which pyroxene it is. Some alternatives are : Diopside, Hedenbergite, Augite or Hypersthene.
The crystals are very dark green to almost black and very easily split basally.
The material thats between the crystals is quartz. There are also some pyrite in the stone.It's a part of a bigger quarts filled cavity in an ultrabasic intrusion.
It's not apatite, not affected by hydrocloric acid.
Color of streak : white.
Hardness of the crystals : 5-6
Collected at Norrmjöle havsbad, 1995.
(300 dpi, 800x600, 41k)

Keep looking on this area, soon to be updated.

If you have some questions, suggestions or comments you are welcome to write me a line or two.

Locality index. Main index.

axelsson@acc.umu.se

	Almandine Small almandine garnets from a quarry near the E4 a couple of km south of Umeå. As a gift from Jorg Alves, 1998. (300 dpi, 800x600, k)
	Andalusite Andalusite crystal in pegmatitic material. The origin of this sample are not shure. It could be outside Umeå, but probably from the quarry at Kåddis. I found it in rocks layd out to protect a bicycle road down the river. Collected 1996. (300 dpi, 800x600, k)
	Andalusite After have heard from one of the more experienced rockhounds here in Umeå that it probably was a crushed garnet, I decided to see what's hiding inside so I chopped off the lower part of the stone. At least it wasn't a garnet. It shows two cleavage planes along the crystal in about 90 degrees, and a square cross section. I still think it's andalusite! It also shows a strong flourescens in green. Collected 1996. (300 dpi, 800x600, k)
	Cordierite Blåbärsbacken consists mostly of gneiss. Where the veins of quartz and feldspar in the gneiss is wider it is possible to find fresh clear and deep purple cordierite. This is one such piece. From Blåbärsbacken, Holmsund. Collected in 2001. Size : 4x3x3 cm.
	Cordierite This is opaque cordierite from the biggest quartz - feldspar vein at Blåbärsbacken, Holmsund. The vein had been blown up into large boulders, up to 200 kg, with the vein running straight through them. It was up to 30 cm wide and contained light blue to black, opaque, cordierite crystals. The cordierite didn't show any crystal faces. From Blåbärsbacken, Holmsund. Collected in 2001. Size : 6x5x3 cm.
	Unknown mineral Unknown crystal in quartz. Most likely a pyroxene crystal. I'm not shure of which pyroxene it is. Some alternatives are : Diopside, Hedenbergite, Augite or Hypersthene. The crystals are very dark green to almost black and very easily split basally. The material thats between the crystals is quartz. There are also some pyrite in the stone.It's a part of a bigger quarts filled cavity in an ultrabasic intrusion. It's not apatite, not affected by hydrocloric acid. Color of streak : white. Hardness of the crystals : 5-6 Collected at Norrmjöle havsbad, 1995. (300 dpi, 800x600, 41k)