Glossar

 

Rocks

The rocks in the Earth’s crust, in the uppermost 30 to 60 kilometres, are in a constant cycle.

The movements are mostly so slow that we are not aware of them.

Mountains are formed and then eroded and sediments are formed from the deposited debris. All rocks can be displaced to great depths where they melt or are altered to form metamorphic rocks. The molten rock or magma solidifies at depth or at the surface as magmatic rock. Then the cycle begins again.

When magma cools in the Earth’s crust it solidifies to form plutonic rocks such as granite.

Magma from volcanoes that reaches the Earth’s surface is termed lava. This solidifies to form volcanic rocks such as basalt. Magma that penetrates into rock fissures and then solidifies forms so-called dyke rocks such as aplite and lamprophyre.

 

Basalt columns form due to delayed cooling of lava, for example in the crater of a volcano. There are no examples of these columns in Switzerland – all the basalts are metamorphic and were overprinted by heat and pressure deep in the earth’s interior. Image: Nagra

 

Examples of magmatic rocks in Switzerland

Granite (plutonic)

Habkern granite, Habkern (Canton Bern). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Alps, crystalline basement beneath the Plateau and the Jura
Origin: Slow cooling of magma at depth, resulting in large interlocking crystals
Main minerals: Feldspar, quartz, mica
Appearance: Light, speckled, massive
Properties: Grainy, very hard, in some locations with joints and dykes
Uses: Floor and façade tiles, blocks for road and waterway engineering, gravestones

 

Volcanic basalt

 

Metamorphic basalt from Alp Flix (Canton Graubunden). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Common worldwide, metamorphic in Switzerland 
Origin: Rapid cooling of lava at the Earth’s surface, hence not fully crystallised
Main minerals: Pyroxene, hornblende, olivine, feldspar
Appearance: Dark grey to black, massive
Properties: Sharp-edged, brittle, weathering-resistant
Uses: Glass wool production, cobblestones

 

Aplite and lamprophyre dyke rocks

Aplite dyke (light) in gneiss (dark), Bergell (Italy). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Solidified magma in rock fissures
Origin: Rapid cooling of lava at the Earth’s surface, hence not fully crystallised
Main minerals (aplite): Quartz, light mica
Main minerals (lamprophyre): Feldspar, pyroxene, hornblende, dark mica
Appearance (aplite): Light and very fine-grained
Appearance (lamprophyre): Dark and fine- to medium-grained
Properties: Hard, easily workable
Uses: Restricted use in Switzerland

Sedimentary rocks are formed by the deposition and gradual solidification of material.

Sandstone and clay and conglomerates such as Nagelfluh consist of material eroded from rock mass. Limestones are formed mainly from shells and other hard parts of sea creatures. Chemically formed sediments such as gypsum and rock salt are formed through evaporation of seawater and lacustrine water. The originally loose components are cemented together with time to form solid rocks. Sediments are often layered.

New sediments are being formed here. Rivers transport rock debris into the plains where they are deposited. With time, these loose gravel deposits form a solid Nagelfluh in the river bed. Image: Nagra

Examples of sedimentary rocks in Switzerland

Nagelfluh (conglomerate)

Nagelfluh, Gottschalkenberg (Canton Zug). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Mainly at the alpine margin
Origin: In the Alps, rocks are reduced to rubble by erosion. Rivers transport this material into the foreland and deposit it in the Molasse Basin
Composition:

Gravels from different alpine rocks (e.g. granite, limestone), cemented and solidified in a fine-grained groundmass

Properties: Forms ridges and steps in the landscape

 

Sandstone

Mica sandstone with chestnut leaf, Kreuzlingen (Canton Thurgau). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Plateau and Alps
Origin: Deposition in river channels and the sea
Composition: Mainly quartz grains and rock fragments, mostly cemented with limestone
Appearance: Grey, rarely red, green and yellow, fine-grained


Properties:

Easily workable, often low durability
Uses: Building bricks, façade tiles, road surfacing, stonemasonry

 

Molasse marl

Molasse marl, Eriz near Thun (Canton Bern). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Plateau and alpine margin
Origin: In river plains and the sea
Composition: Very fine-grained mix of calcite, clay and other mineral and rock grains
Appearance: Multi-coloured, layered
Properties: Mostly dense, soft after weathering at the surface
Uses: Brickworks products

 

Clay

Opalinus Clay from the Mont Terri Rock Laboratory (Canton Jura). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Jura and northern parts of Switzerland and the Alps
Origin: Deposition in the sea
Composition: Clay minerals, quartz, little calcite
Appearance: Different coloured, often layered
Properties: Dense, soft; clay minerals swell on contact with water
Uses: Sealing clay for disposal sites and dams, clay bricks and cement production

 

Verrucano

Verrucano from the Permian, Riniken borehole (Canton Aargau), depth around 1013 metres. Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Alps, deep underground troughs of Northern Switzerland
Origin: Deposition of eroded material from a former mountain on the mainland, cemented and solidified
Composition: Angular fragments in sandy-clayey groundmass
Appearance: Red-brown with light rock fragments
Properties: Not very durable
Uses: Previously as building stone

 

Limestone

Öhrlikalk, Öhrlisattel (AI). Image: Collection Urs Oberli, St. Gallen

Occurrence: Jura and Alps
Origin: Deposition of hard parts of organisms on the sea floor
Composition: Mainly calcite
Appearance: Mostly light to blue grey, fine-grained
Properties: Easily workable
Uses: Floor tiles, building bricks, cement production, lime plaster

 

Anhydrite and gypsum

Anhydrite between clayey shale (below) and gypsum (above), Simplon tunnel (Canton Valais). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Tabular and Folded Jura, Alps
Origin: Precipitation from seawater due to evaporation
Main minerals: Gypsum and anhydrite; gypsum contains confined water, anhydrite is anhydrous
Appearance: White to dark grey, coarse-grained, banded
Properties: Soft
Uses: In the construction industry as gypsum plaster, special gypsum, plasterboard, production of cement and porous concrete, modelling and moulding plaster, production of sulphuric acid

Increased pressure and temperature deep underground result in alteration of all types of rocks to metamorphic rocks by changing their structure or composition.

This can lead to formation of new minerals that can grow in a preferred direction, namely perpendicular to the largest pressure component.

Metamorphic rock structures at the Grimsel Test Site. Image: Comet

Examples of metamorphic rocks in Switzerland

Gneiss

Gneiss, Central Alps. Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence:

Alps, crystalline basement beneath the Plateau and the Jura

Origin: Rock altered by increased pressure and temperature, produced from granite for example
Main minerals: Feldspar, quartz, mica
Appearance:

Light speckling, thick-layered with augen structure due to orientation of minerals

Properties: Weathering-resistant, fissile. Can be strongly fractured and penetrated by dykes
Uses: Kerbstones, stonework, floor and façade tiles, roofing

 

Schist

Hornblende-Garbenschiefer, Val Tremola (Canton Ticino). Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence:

Alps, crystalline basement beneath the Plateau and Jura

Origin:

Metamorphosis of clay-rich parent rock

Main minerals: Mainly mica with different minerals
Appearance:

Shiny, dark, thin-layered due to mineral orientation

Properties: Easily fissile along smooth cleavage planes
Uses: Floor and façade tiles, roofing

 

Marble

Marble, Central Alps. Image: Earth Science Collections ETH Zurich, Urs Gerber

Occurrence: Alps
Origin: Metamorphosis of limestone and dolomite
Main minerals: Calcite (lime marble), dolomite (dolomite marble)
Appearance: Grainy, light, partly banded
Properties: Easily workable
Uses: Floor and façade tiles, tiling, sculpture

ROCKS FORM IN A SLOW CYCLE BETWEEN THE EARTH’s SURFACE AND THE DEEP CRUST