Earth's Dynamic Processes: Rocks, Minerals, and Geological Forces

External Geological Agents and Processes

External agents are those capable of producing changes on geological materials. These include water in its three states, wind, temperature changes, atmospheric gases, and living organisms. Their action leads to relief formation. External agents act through four primary processes: weathering, erosion, transportation, and sedimentation.

Understanding Weathering

Weathering is the alteration of rocks by fracture, dislocation, or chemical reactions, without the resulting fragments being displaced. Mechanical weathering is the breaking of rock into blocks or particles through physical processes.

Types of Water Bodies and Flows

Inland water circulating without a fixed course, originating from rainfall, is called wild water. When rainwater runs through small streams or channels, it forms water streams.

Characteristics of Torrents

Torrents are short channels that carry water only sporadically; their activity is generally seasonal. They are distinguished by three parts: the watershed, the drainage channel, and the alluvial fan. Rivers are natural streams of water circulating permanently through a fixed channel. Their flow rate may vary due to rain, snowmelt, or groundwater inflow.

Minerals: Composition and Properties

Minerals are natural, inorganic matter composed of the most abundant chemical elements in Earth's crust. They are found in deposits and appear in rocks as filled fissures or cracks. Physical properties such as hardness, fracture, and exfoliation give unique characteristics to each mineral.

Defining Amorphous Matter

Amorphous Matter: These are solids whose atoms do not occupy a fixed place in space or follow a geometric pattern.

Understanding Rock Types

Igneous Rocks: Formation and Classification

Igneous Rocks: Formed by the cooling of molten minerals (magma or lava), they appear as a melt. Examples include granite and pumice. The classification of igneous rocks is based on their mineralogical composition and textures. Textures help distinguish between plutonic, volcanic, and hypabyssal (filonianas) rocks.

Metamorphic Rocks: Transformation and Characteristics

Metamorphic Rocks: Formed from pre-existing igneous or sedimentary rocks that have undergone significant changes due to heat, pressure, or chemical alteration. Examples include slate and marble. The classification of metamorphic rocks is primarily based on their mineralogical composition, texture (with grain size and the presence or absence of foliation being key factors), and the initial rock type from which they formed.

Sedimentary Rocks: Origin and Formation

Sedimentary Rocks: These rocks originate primarily at the bottom of seas or lakes and appear as masses of different substances. Examples include limestone and gypsum. Sedimentary rocks result from the alteration, transport, and sedimentation of any previous rock. The minerals formed can be the same as those in the disintegrated parent rock (after physical transport and deposition), or they may be new minerals formed by the chemical alteration of pre-existing ones (known as alteration minerals). Sedimentary rocks are formed when compact sediments undergo sedimentation and are cemented into a hard rock. This phenomenon typically occurs at relatively large depths where pressure is exerted by overlying sediment layers.