The rock cycle is very important to us because it explains the way the different types of rocks are formed on earth.
The rocks currently visible on the Earth’s surface have moved through transition stages that transformed them from one form into another. The importance of the rock cycle lies in how it forms and recycles the various layers that make up the Earth. To do this, the cycle moves through three different stages that produce three different types of rock. Igneous rock makes up the foundation on which the Earth’s continents sit. This type of rock is made as magma cools over time, crystalline structures begin to form.Volcanic eruptions send magma across the Earth’s surface as well as into underground layers.
The magma that settles underground cools slower than what makes its way to the Earth’s surface. In effect, igneous rock can form on the surface or within the underground layers. Volcanic Rocks (also called extrusive igneous rocks) include all the products resulting from eruptions of lava (flows and fragmented debris called pyroclasts). Plutonic Rocks (also called intrusive igneous rocks) are those that have solidified below ground; plutonic comes from Pluto, the Greek god of the underworld. Metamorphic rocks are created when other types of rocks are transformed due to great pressure and heat within the earth. The meaning of the term ‘metamorphic’, in fact, is ‘changed’.
When igneous rocks, or sedimentary rocks, or even metamorphic rocks get buried very deep under the earth’s surface, a process that takes millions of years, they get changed into something else by the enormous pressure and heat inside the earth. The foliation or layering that occurs in many types of metamorphic rocks is because of the immense directional pressure they undergo deep within the earth, usually along the boundary of a converging plate tectonic.Gneiss: This metamorphic rock is classified as high grade, which means that compared to schist it has been subjected to more pressure Sedimentary rocks form from igneous formations as the weathering effects of wind and water break igneous materials into sediment fragments on the Earth’s surface. The rocks exposed to these forces expand under the glaring heat of the sun, contract under the onslaught of ice and cold. The wind that blows against the top of the rocks of mountains erodes them, dust particle by dust particle.
Chemical sedimentary rocks form when stagnant water evaporates, leaving dissolved minerals in it behind.Sedimentary rock formations of this type are commonly observed in arid lands. Physical Properties Color Most minerals have a distinctive color that can be used for identification. In opaque minerals, the color tends to be more consistent, so learning the colors associated with these minerals can be very helpful in identification. Streak Streak is the color of the mineral in powdered form. Streak shows the true color of the mineral.
In large solid form, trace minerals can change the color appearance of a mineral by reflecting the light in a certain way.Cleavage & Fracture Minerals tend to break along lines or smooth surfaces when hit sharply. Different minerals break in different ways showing different types of cleavage. Cleavage is defined using two sets of criteria. The first set of criteria describes how easily the cleavage is obtained. The second set of criteria is the direction of the cleavage surfaces.
The names correspond to the shape formed by the cleavage surfaces: Cubic, rhombohedra, octahedral, dodecahedral, basal or prismatic. Crystalline Structure Mineral crystals occur in various shapes and sizes.The particular shape is determined by the arrangement of the atoms, molecules or ions that make up the crystal and how they are joined. This is called the crystal lattice.
There are degrees of crystalline structure, in which the fibers of the crystal become increasingly difficult or impossible to see with the naked eye or the use of a hand lens. Transparency or Diaphaneity Diaphaneity is a mineral’s degree of transparency or ability to allow light to pass through it. The degree of transparency may also depend on the thickness of the mineral.
