Rocks are formed, altered and then break down again in a continuous cycle. Three types of rock are part of the cycle: igneous rocks, metamorphic rocks and sedimentary rocks. They all basically consist of mineral components, which also include natural glasses. They can also contain originally organic material such as animal remains or plant components. Learn more about Switzerland’s rocks in the following sections.
In a nutshell: explaining the rock cycle in 3 minutes
Geological timescales vs. radioactive waste decay periods
The rock cycle progresses over a geological timescale of several hundred million years. The time period relevant for the disposal of radioactive waste is a mere fraction of this: safety analyses for a deep geological repository for high-level waste “only” have to consider a period of one million years. To protect humans and the environment during this period, the waste must be contained deep underground in stable rock formation.
For Nagra to safely dispose of the waste deep underground, it needs in-depth knowledge of the suitable rocks and their properties. In Switzerland, the Opalinus Clay was identified as the most suitable rock for a deep geological repository after years of thorough research. You can learn more about the Opalinus Clay and other rocks on a guided tour tvistihrough the Swiss underground research laboratories.
Rock cycle
(For a complete view of the image, click on its left)
The rocks within the uppermost 30 to 60 kilometres of the earth, the earth’s crust, are in a continuous cycle.
These cyclical movements are mostly so slow that we are not aware of them. Mountains form, and the rocks exposed at the surface are weathered. The mountains are eroded, and the debris is carried off in rivers and deposited elsewhere. Sedimentary rocks are formed from the eroded materials.
All rocks can reach great depths where they melt or are altered to form metamorphic rocks. The molten rock, or magma, solidifies at depth or at the earth’s surface as magmatic rock, and the cycle begins anew.
1. Igneous rocks
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 called lava. This solidifies to form volcanic rocks such as basalt. Some magma also rises from below through narrow dykes and rock fissures. If this magma cannot reach the surface, i.e. if it gets stuck on its way up and solidifies, dyke rocks such as aplite and lamprophyre form as a result.
Here are some examples of magmatic rocks that can be found in Switzerland:
Granite (plutonic)
Occurrence:
Alps, crystalline basement beneath the Swiss Plateau and Jura Mountains
Formation:
Slow cooling of magma at depth, resulting in large interlocking crystals
Composition:
Feldspar, quartz, mica
Appearance:
Light, speckled, massive
Properties:
Grainy, very hard, in some locations with numerous joints and dykes
Uses:
Floor and façade tiles, blocks for road and waterway engineering, gravestones
Volcanic basalt
Occurrence:
Common worldwide, metamorphic in Switzerland
Formation:
Rapid cooling of lava at the earth’s surface, hence not fully crystallised
Composition:
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
Occurrence:
Solidified magma in rock fissures
Formation:
Rapid cooling of lava at the earth’s surface, hence not fully crystallised
Composition of aplite:
Quartz, light mica
Composition of lamprophyre:
Feldspar, hornblende, pyroxene, dark mica
Appearance of aplite:
Light-coloured and quite fine-grained
Appearance of lamprophyre:
Dark and fine- to medium-grained
Properties:
Hard, easily workable
Uses in Switzerland:
few
2. Sedimentary rocks
Photo: Switzerland’s “Wasserschloss”, the confluence of three rivers in Canton Aargau: Aare, Reuss and Limmat. New sediments also form at this point. The rivers transport rock debris to the plains where they are deposited. With time, these loose gravel deposits form a solid nagelfluh.
Sedimentary rocks are formed from materials (such as eroded materials from mountains, mud, sand or salt) deposited on land or in the water where they gradually solidify. The originally loose components are cemented together over time to form solid rocks. Sedimentary rocks are often layered. Conglomerates, such as nagelfluh, sandstone and clay, consist of eroded materials from mountains. Limestones are formed mainly from shells and other hard parts of sea creatures. Chemically formed sediments such as gypsum and rock salt are formed when marine and lacustrine waters evaporate.
Here are some examples of sedimentary rocks that can be found in Switzerland:
Nagelfluh (conglomerate)
Occurrence:
Mainly at the alpine margin
Formation:
In the Alps, rocks are reduced to debris 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 into a fine-grained ground mass
Properties:
Forms ridges and steps in the landscape
Sandstone
Occurrence:
Swiss Plateau and Alps
Formation:
Deposition in river channels and the sea
Composition:
Mainly quartz grains and rock fragments, mostly cemented with limestone
Appearance:
Grey, more rarely red, green and yellow, fine-grained
Properties:
Easily workable, often low durability
Uses:
Building bricks, façade tiles, road surfacing, stone masonry
Molasse marl
Occurrence:
Swiss Plateau and alpine margin
Formation:
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 earth’s surface
Uses:
Brickwork products
Clay
Occurrence:
Jura and northern parts of Switzerland and the Alps
Formation:
Deposition in the sea
Composition:
Clay minerals, quartz, some calcite
Appearance:
different colours, often layered
Properties:
Soft, dense; clay minerals swell on contact with water
Uses:
Sealing clay for disposal sites and dams, production of clay bricks and cement
Limestone
Occurrence:
Jura and Alps
Formation:
Deposition of hard parts of organisms on the sea floor
Composition:
Mostly calcite
Appearance:
Mostly light- to blue-grey, fine-grained
Properties:
Easily workable
Uses:
Floor tiles, building bricks, cement production, lime plaster
Anhydrite and gypsum
Occurrence:
Tabular and Folded Jura, Alps
Formation:
Precipitation from seawater due to evaporation
Composition:
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
3. Metamorphic rocks
Photo: Metamorphic rock structures at the Grimsel Test Site.
Due to increased pressure and temperature deep underground, the structure and composition of all types of rocks change, and they become metamorphic. During this process, new minerals can form. These tend to grow in a preferred direction, namely perpendicular to the largest pressure component.
Here are some examples of metamorphic rocks that can be found in Switzerland:
Gneiss
Occurrence:
Alps, crystalline basement beneath the Swiss Plateau and Jura Mountains
Formation:
Rock altered by increased pressure and temperature, for example, produced from granite
Composition:
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, building bricks, floor and façade tiles, roofing
Schist
Occurrence:
Alps, crystalline basement beneath the Swiss Plateau and Jura Mountains
Formation:
Metamorphosis of clay-rich parent rock
Composition:
Mainly mica with a variety of other minerals
Appearance:
Shiny, dark, thin-layered due to mineral orientation
Properties:
Easily fissile along smooth cleavage planes
Uses:
Floor and façade tiles, roofing
Marble
Occurrence:
Alps
Formation:
Transformation (metamorphosis) of limestone and dolomite
Composition:
Calcite (lime marble), dolomite (dolomite marble)
Appearance:
Grainy, light, partly banded
Properties:
Easily workable
Uses:
Floor and façade tiles, tiling, sculptures
Photos of the individual rock types with the exception of the Öhrlikalk: Earth Science Collections of the Swiss Federal Institute of Technology Zürich / Urs Gerber
Photo of the Öhrlikalk: Collection Urs Oberli, St. Gallen
