In the second climbers' guide we look at limestone. Formed mainly from calcite, CaCO3, limestone is a common (and very popular for climbing) rock type.
Large limestone deposits formed across extensive low-lying continental regions when sea levels were higher, during the Carboniferous (Most UK climbing limestone), Jurassic (most European Sport venues and South coast of England) and Cretacious (the Chalk - only for the most extreme of us!). Much of what makes limestone so popular for climbing stems from the fact that it is soluble in water, forming solution features such as pockets, pavements and caves (shout out to any cavers). When that water reaches a free surface, such as a cliff face, it evaporates leaving the dissolved carbonate behind as tufas.
Beacuse limestone is typically fine-grained and just made of one type of mineral it takes a very fine polish - the one downside to popular limestone routes.
Dolomite is a magnesium-rich form of limestone (the mineral dolomite is CaMg(CO3)2) which is more resistant to erosion - so doesn't polish as badly - than calcium-carbonate limestones. Think of the Dolomites in Northern Italy, named after the rock type.
