Breccia is a clastic sedimentary rock composed of large angular fragments of rocks or minerals (over 2mm millimetres in diameter) cemented together by a matrix of smaller particles that can be similar or not to the composition of its fragments and a mineral cement that bonds the rock together. The most common cement minerals are silica, calcite and iron oxides.
There are many compositions of Breccia. The composition is determined by the mineral material and rock that the angular fragments were produced from. This is influenced by climate, weather conditions and soil composition.
The properties of breccia are highly variable and they can occur in any colour, and may be either hard or soft in structure. Depending on the mineral or material its clasts are made of, breccias can be categorised and commercially sold as marble or other type of natural stone, whilst – in reality – they are a stand-alone category. The most commonly known breccias are Calacatta Viola and Breccia Capraia.
Sedimentary Breccia is a type of clastic sedimentary rock, which is characteristically composed of angular to sub-angular, randomly oriented clasts of other sedimentary rocks. A conglomerate, by contrast, is a sedimentary rock composed of rounded fragments or casts of pre-existing rocks. One of the most known conglomerate is Ceppo di Gre’.
The morphology of breccia offers a beautiful game of contrasts between the background and the veins, formations and casts, making breccia amongst the most dynamic (or busy, some would say) materials.
Breccia forms where broken, angular fragments of rock or mineral debris accumulate. Therefore one of the most common locations for breccia formation is at the base of an outcrop where mechanical weathering debris accumulates. Another is in stream deposits a short distance from the outcrop or on an alluvial fan.
There are different types of breccia. Volcanic breccia, pyroclastic, or igneous breccia is formed from the compaction of lava chunks with ash. Collapse breccia is sedimentary breccia formed from the collapse of a cavern. Impact breccia is formed from a meteor impact breaking rock at the impact site.
Hydrothermal breccias are usually formed by hydrofracturing of rocks by highly pressured hydrothermal fluids. Hydrothermal breccias usually form at shallow crustal levels (<1 km) between 150 to 350 °C, when seismic or volcanic activity causes a void to open along a fault deep underground.
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