What the wall is — atomic, mineral, and in the hand. So granite, limestone and sandstone are more than names.
Every crag falls into one of these three families — or a mix, when the Alps rebuilt the rock again.
Cooled magma
Melt cools and crystallises. Plutonic rock (granite, gabbro) cools slowly underground — coarse crystals. Volcanic rock (basalt, porphyry, rhyolite) cools fast at the surface — fine, or with phenocrysts.
Often good friction and cracks. Cam country. Crystals can be sharp or crumbly, depending on weathering.
Deposited rock
Grains, shells or chemical precipitate are deposited and lithified (diagenesis). Cement: silica, calcite, clay, iron oxides.
Limestone: pockets, solution holes, polish. Sandstone: rounded holds, often off-limits after rain. The cement decides how solid the rock is.
Transformed rock
Existing rock recrystallises under pressure and heat without melting. Foliation, banding, harder minerals.
Gneiss often climbs like granite, but in layers. Quartzite is extremely hard and high-friction. Mica schist can be slabby and unreliable.
Silicates (granite, gneiss, sandstone) live off the tetrahedron. Carbonates (limestone, dolomite) off the flat triangle. How the blocks link sets cleavage — and whether a crack holds or a flake blows.
Silicon in the centre, four oxygens at the corners — like a pyramid with triangular faces. That is the building block of almost all igneous and metamorphic climbing rock. Tetrahedra share corners (oxygen atoms) and build chains, sheets or full frameworks.
One carbon, three oxygens in a plane. With calcium or magnesium you get calcite (CaCO₃) or dolomite (CaMg(CO₃)₂) — the stuff of limestone and dolomite walls. Flat building blocks, three cleavage planes, soluble in (slightly) acidic water.
The tetrahedra alone would be negatively charged. Cations fill the gaps and set hardness, colour and cleavage. Aluminium can replace silicon in the tetrahedron (feldspar). Iron often colours rock dark or rust-red.
Quartz, feldspar
Each tetrahedron shares all four corners. A 3D net — little to no cleavage, hard. That is why granite holds cams: the crack goes through the rock, not along a mica layer.
Mica, clay minerals
Tetrahedra in layers, weak bonds in between. Perfect cleavage — mica peels, clay swells when wet. Clay-cemented sandstone goes soft after rain; gneiss with lots of mica can break in slabs.
Pyroxene, amphibole (hornblende)
Tetrahedra in single or double chains. Typical in dark igneous rock (gabbro, basalt). Two cleavage directions, often dark, elongated crystals.
Rock is a mix. The individual minerals have formulas, hardness and cleavage — the mix inherits friction and fractures.
Framework silicate. Each SiO₄ tetrahedron shares all corners — formula SiO₂, no cleavage, Mohs 7.
Pale, glassy mineral in granite, gneiss, sandstone, quartzite.
Gives friction and hard edges. Cracks in quartz are often bomber. Wet quartz can be slick, but it does not break in slabs.
Framework silicate in which Al replaces some of the Si. Two cleavage planes ~90°. Potassium feldspar (pink), plagioclase (white–grey).
By volume the most common mineral in the Earth’s crust — main constituent of granite and gneiss.
The coarse crystals in granite are often feldspar. It weathers to clay — then holds crumble. Fresh: good edges, a bit less friction than quartz.
Sheet silicate. One perfect cleavage plane — peels into paper-thin flakes.
Muscovite (pale) and biotite (black) in granite and gneiss. Glitters in the sun.
Lots of mica = foliated, slippery, unreliable flakes. Cams in mica-rich layers can blow. Tap it before you trust it.
Carbonate. Planar CO₃ groups, calcium in between. Three cleavage planes (rhombohedron), Mohs 3 — scratchable with a knife, fizzes with acid.
Main mineral of limestone and marble. Cement in some sandstones.
Pockets and solution holes form because water dissolves calcite. Polish on well-climbed holds. Wet limestone is clearly slicker than wet granite.
Like calcite, but every second calcium is replaced by magnesium. A bit harder and less soluble than pure limestone.
The Dolomites, parts of the Northern Limestone Alps, some of the Jura.
Often yellowish-grey, a bit rougher than pure limestone. Take brittle bands and yellow zones seriously — magnesium changes the weathering, not the basic rule (carbonate).
Isolated tetrahedra (olivine) or chains (pyroxene, hornblende). Iron-rich, dark green to black.
Gabbro, basalt, peridotite — dark, heavy rock.
Basalt can be sharp and positive (columns, edges) or glassy-smooth. Gabbro climbs coarse-crystalline like dark granite.
Composition, fabric, climbing feel and how you protect it. For the main rocks, a massif to place them — plus close-ups so crystals, grains and banding are visible.
Swisstopo
Swisstopo map with the Lithology 500 layer: main rock types of Switzerland at a glance. Geology theme, grey national map.
Examples: Furkapass, Grimsel, Yosemite; Elbsandstein is *not* granite — Saxon Switzerland is sandstone.
Examples: Aar massif, Ticino, Murgtal / crystalline rock in the Black Forest, parts of the Central Alps.
Examples: Bolzano / South Tyrol (quartz porphyry), Estérel (red rhyolite porphyry), some of the Black Forest, parts of the Vosges.
Examples: Eifel, Northern Ireland (Giant’s Causeway as an extreme), some Inn valley porphyry/basalt, Iceland.
Examples: Rare as a sport crag, scattered in ophiolite zones (e.g. parts of the Western Alps).
Examples: Jura, Danube valley, Rätikon, Dolomites (often dolomite), Calanques, Verdon, Frankenjura.
Examples: The Dolomites, parts of the Northern Limestone Alps, some of the Swiss Jura.
Examples: Saxon Switzerland, Pfalz, Fontainebleau (sandstone boulders); Indian Creek is *not* classic sandstone sport — crack trad in sandstone.
Examples: Meteora, some Alpine molasses rock, scattered in the Jura.
Examples: Parts of the Western Alps, Scandinavia, some Appalachian quartzite (USA).
Examples: Bündnerschiefer, parts of the Eastern Alps — more alpine than crag.
One hand on the block, tap with the other. Vibration = not solid. Applies to all rock, especially limestone bands and gneiss layers.
Limestone and sandstone lose clearly more friction than granite. Clay-cemented sandstone can soak and go soft.
Calcite (Mohs 3) polishes smooth on well-climbed routes. Quartz (Mohs 7) stays rougher — that is why a 6a in the Jura feels different from a 6a at the Furkapass.
Granite/gneiss: cooling joints, often parallel → cams. Limestone: solution and bedding planes, often V and pockets → nuts and tricams.
Cams vs. nuts by rock type: Trad protection → · Practice crags under Tour planning →
Simplified geology for climbing — local variants and weathering on site count more than the textbook formula.