Rocks and Earth Materials

Crystalline rock, any rock composed entirely of crystallized minerals without glassy matter. Intrusive igneous rocks—those that congeal at depth—are virtually always crystalline, whereas extrusive igneous rocks, or volcanic rocks, may be partly to entirely glassy. Many factors influence the ability of a magma to crystallize, but the length of time during which cooling occurs is the controlling factor. Metamorphic rocks are almost always crystalline; the term crystalline schists has been applied to indicate all rocks of metamorphic origin, and thus the term crystalline rocks may be taken to mean an igneous origin. Sedimentary rocks can also be crystalline, such as the crystalline limestones precipitated directly from solution; the term is not generally applied to the clastic sediments, even though they are formed largely from the accumulation of crystalline materials.

The metals at the bottom of the activity series are the least reactive. They are often found in a free state. For example, gold, silver, platinum and copper are found in the free state. Copper and silver are also found in the combined state as their sulphide or oxide ores. The metals at the top of the activity series $(K, Na, Ca, Mg$ and $Al)$ are so reactive that they are never found in nature as free elements. The metals in the middle of the activity series $ (Zn, Fe, Pb, etc.)$ are moderately reactive. They are found in the earth’s crust mainly as oxides, sulphides or carbonates. The ores of many metals are oxides. This is because oxygen is a very reactive element and is very abundant on the earth.

A river joined by its tributaries, at approximately right angles, develops a trellis pattern. A trellis drainage pattern develops where hard and soft rocks exist parallel to each other. The dendritic pattern develops where the river channel follows the slope of the terrain. 

Sedimentary rocks are made up of grains of sediment that have been weathered from a pre-existing rock or mineral. The grains can be big or small, they are often rounded, and are cemented together in a matrix. Sedimentary rocks may be layered and may also contain fossils.

Open system is defined as a system wherein there is free exchange of both matter and energy with the surroundings. The system has interaction with the external environment. All the systems on Earth are called as open systems. Earth is an open system for energy. 

Impervious rocks are rocks which squeeze both oil and gas between them. Petroleum is obtained deep down from these impervious rocks.

Scientific consensus suggests that life on Earth originated in the oceans (hydrosphere), where early chemical reactions in a 'primordial soup' led to the development of the first simple organisms.

Primordial soup refers to the hypothetical solution of organic compounds in the early Earth's oceans, which provided the environment for the synthesis of life's building blocks.

Lichen can grow on barren rock and are the first living organisms or "pioneers" to colonize places, where no other living things can survive.

• The weathering of rocks is responsible for the formation of soil. It occurs due to a variety of reasons like under the effect of lichens. 
• Lichens cause the breakdown of rock materials and organic minerals. Thus they breakdown the surface of rocks.
• Mosses also release different gases and cause the breakdown of rocks they grow on.
• Roots of plants that grow on rocks cause cracks on the surface of rocks.
• Thus, all these factors are responsible for the weathering of rocks.

Lichens are classified by their substrate: saxicolous lichens grow on rocks, corticolous on bark, lignicolous on wood, and terricolous on soil.

• An inexhaustible resource is one that is replaceable, while an exhaustible resource is not replaceable.
  
• Minerals are natural resources and they cannot be replaced by man.
  
• Therefore, the constant use of minerals at this rate will lead to their exhaustion. Thus, they are considered as exhaustible natural resources.
  

Minerals are deposited and accumulated in the stratas of sedimentry rocks.

Minerals are found in layers or strata in sedimentary rocks. Minerals are accumulated in horizontal strata after being exposed to high heat and pressure for a long period of time. Coal, iron ore, gypsum, potash salt etc are formed in this way.