Forsnacken

Mineral became solid and formed crystals

The bubbles contained various solutions of minerals depending on the composition of elements in the rock. As the magma cooled the bubbles were stabilised in the form of cavities. In the openings of the cavities the mineral grew (out of the solutions in the bubbles) at their own pace. Once they had hardened they formed large crystals. The more time they had to grow the larger the crystals became.

The rock wall part of a magma chamber

The rock wall of Forsnacken is part of a 1,500 million year old magma chamber. The chamber was formed of masses of molten rock, magmas that pushed upwards from deep within the earth and gathered a few kilometres below the earth´s surface. Since then all the material that had been above the chamber has weathered and eroded making it possible for you to look right into the chamber.

Masses of molten rock became red granite and dark gabbro

When in due course the magmas cooled and hardened they formed rocks. One magma was red and became granite, the other was dark, almost black, and became gabbro.

Pulses of warm magma of different compositions were continuously adding to the magma chamber from below – think of a lava lamp. Magma that had already solidified could then heat up and become liquid again.

The magmas floated around and formed patterns

The magmas interacted in batches, forming different patterns depending on whether they were liquid at the same time or not.

Gabbro and granite melt at different temperatures. Gabbro is several hundred degrees warmer when melted compared to granite. The difference in temperatures between the two magmas meant that they would not fully blend everywhere.

Magma mingling – "pillows" of gabbro in granite

In many places you can see patterns of the gabbro in the granite, looking like pillows. This is called magma mingling and occurred at the time when both magma types were partially liquid at the same time.

The magmas may have been cold, hot or tepid at the time of the encounters. Around the gabbro you can sometimes spot a darker outer edge; this appeared when the warmer gabbro cooled off quicker in contact with the colder granite.

Magmatic breccia – angular fragments of gabbro in granite

At times the gabbro magma had started to cool off or become cold before a new pulse of hot granite magma came pushing upwards. This would cause the gabbro to crack and break into angular fragments. This is called magmatic breccia.

In case the almost solid granite encountered a pulse of hot gabbro, the granite may have been a bit burned by the gabbro. This would be seen as a white edge around the granite.

Magma mixing - mixed magmas

When magma had the possibility to harden slowly it remained warm for longer and heated up its environment. Magmas of different compositions could blend and become solid at the same time. Crystals from one of the magmas could merge with another and eventually dissolve. A new rock was formed, a sort of hybrid rock.

Hybrids contain minerals that in normal circumstances would not co-exist. The rocks can be difficult to see and identify since they can appear in so many different ways.