Answer:
a) The three main types of rocks are: sedimentary, metamorphic, and igneous and they differ considering how they were formed.
b) Five key processes by which soil is formed are: leaching, eluviation, illuviation, podsolisation and gleying.
Explanation:
a)
Sedimentary: formed by the accumulation or deposition of small particles of sand, shells, pebbles, and other fragments of material, commonly known as sediment. Sediment accumulates in layers, and over a long period of time, it hardens. However, it does not accumulate everywhere, but these particles are carried to the places of accumulation by air, water, ice, mass movement or glaciers. This is usually the type of rocks in which we can find fossils.
The examples of sedimentary rocks: limestone, sandstone, coal, dolomite.
Metamorphic: were once igneous or sedimentary rocks, but have been changed under the surface of the earth due to intense heat and pressure (squeezing). They could be foliated or non-foliated. The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface.
The examples of metamorphic rocks: gneiss, phyllite, schist (foliated) and hornfels, marble, quartzite (non-foliated).
Igneous: formed by cooling and solidification of magma or lava. The name 'igneous' comes from the Latin word 'igneous' which means fire. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (lava). When lava cools very quickly, the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.
The examples of igneous rocks: diorite, gabbro, granite, pegmatite, basalt and obsidian.
b)
Leaching: the loss of water-soluble plant nutrients from the soil, caused by rain and irrigation. What can affect leaching is crop planting, soil structure and fertilizers.
Eluviation: soil particles held in suspension, such as clay, are removed (washed away).
Illuviation: soil particles held in suspension, such as clay, are accumulated.
Podsolisation: happens when strongly acid soil solutions cause the breakdown of clay minerals. Consequently, silica, aluminium and iron form complexes with organic substances in the soil. These minerals disappear from the surface and can accumulate in distinct dark sub-surface layers.
Gleying: happens in waterlogged, anaerobic conditions when iron compounds are reduced from the soil, or segregated out. It can often be found in marshy wetlands.
