Sedimentary rocks - Info pack

Sedimentary rocks are a fascinating category of rocks that form from the accumulation of sediment over time, predominantly in water bodies like lakes and oceans. The sediments that make up these rocks can range from minerals to tiny organic particles and plant debris. Over time, these deposits are compressed and solidify into rock layers known as strata, which are often visible in exposed cliff faces. Despite their widespread coverage of the Earth's surface, sedimentary rocks represent only a small portion of the Earth's crust, especially when compared to igneous and metamorphic rocks. Common examples of sedimentary rocks include limestone, sandstone, mudstone, chalk, coal, claystone, and flint. Interestingly, when sedimentary rocks like limestone and sandstone are subjected to extreme heat and pressure, they undergo a transformation known as metamorphism, resulting in the formation of metamorphic rocks such as marble and quartzite, respectively.

The formation of sedimentary rocks is a natural process that begins with the erosion of existing rocks by water or ice, which then deposits the eroded material into rivers, lakes, and oceans. Over millions of years, these particles accumulate in layers, eventually becoming buried deep enough to experience pressure and temperature changes that cement them into rock. This cycle is ongoing, with the rocks resurfacing through continental collisions and other geological forces. Specific types of sedimentary rocks, such as coal, conglomerate, and limestone, have unique origins. Coal forms from the concentrated carbon of dead vegetation in swamps under high pressure and temperature. A conglomerate consists of varied-sized particles, including pebbles and sand grains. Limestone typically originates from the calcium carbonate of sea creature exoskeletons and can also form from lime mud and debris along coastlines, which, upon burial, recrystallise into this common sedimentary rock.