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Rocks and Minerals

Magmatic (or igneous) rocks are formed by the cooling and solidification of magma. They are the oldest rocks in the Earth's crust.
Types:
Intrusive (plutonic): They cool slowly inside the Earth, forming large crystals.
Ex.: Granite, diorite.
Extrusive (volcanic): They cool quickly at the surface, with small or non-existent crystals.
E.g.: Basalt, obsidian.
Examples:
Granite: Used in construction.
Basalt: Common in fertile soils (e.g.: terra preta).
Obsidian: Glassy rock used in ornaments.
These rocks are fundamental for geological studies.

Metamorphic rocks are formed by the transformation of other rocks (igneous, sedimentary or metamorphic) due to high pressure and/or temperature, without melting.
Features:
Foliated texture: Minerals organized in layers (e.g.: gneiss, schist).
Non-foliated texture: No layers, solid appearance (e.g. marble, quartzite).
Examples:
Marble: Originates from limestone.
Quartzite: Derived from sandstone.
Gneiss: Comes from granite.
Shale: Results from mudstones/metapelites.
These rocks are widely used in construction and decoration.

Do you know the Karst relief??
The Amiais stream, a small tributary of the Alviela river, is responsible for one of the interesting examples of interaction between water and limestone rock and, Portugal. At a certain point during its journey to the surface, the stream falls and disappears inside the rock through a cave built due to erosion caused by the passage of water over thousands of years.
About the characteristic forms of the karst relief and legend of the figure:
A (Algar)
B (Dolina)
C (Lapiás)
D (Sumidouro)
E (Stalactite)
F (Stalagmite)
G (Cave)
H (Resurgence)

Rocky cliffs and beaches are common sedimentary landscapes on the Portuguese coast, incessantly shaped by the action of the sea and wind. In several regions of the Atlantic coast in Portugal, the wind is capable of transporting and accumulating sand, resulting in the formation of dunes. Furthermore, rivers carry a large amount of rocky materials that are deposited in their beds and banks, contributing to the formation of river deposits.

The karst model is a sedimentary landscape typical of regions dominated by limestone. Rainwater dissolves the limestone, creating cracks that deepen, forming underground wells and caves. The continuous infiltration of water into the limestone promotes its dissolution and feeds the underground watercourses.
The lapiás fields, sinkholes, sinkholes and caves are some geological forms characteristic of the karst model of limestone regions.

The diversity of sedimentary rocks and the geological processes that give rise to them, whether through detrital, chemical or biogenic processes, results in a wide variety of sedimentary landscapes.
A sedimentary landscape is one formed by rocks resulting from the deposition of materials, such as grains or fragments of other rocks, substances dissolved in water or remains of living beings. These rocks are often organized into layers or strata, which are visible in landscapes.

Sedimentary rocks are classified based on the origin of the sediments, divided into three groups: Detrital Rocks, formed by the compaction and cementation of fragments of other rocks, such as ballast, sand and clay; Chemiogenic Rocks, originated by the precipitation of substances dissolved in water, such as limestone and rock salt; and Biogenic Rocks, which have biological origin, accumulating remains of living beings or products of their activity, such as coal and conquiferous limestone. Each group represents a distinct training process.

The formation of sedimentary rocks goes through several stages. Sedimentogenesis encompasses processes such as: Weathering, which alters rocks by agents such as water, temperature, atmospheric gases or living beings. Meteorization can be Physical, maintaining the chemical composition, or Chemical, modifying the minerals. Erosion removes materials resulting from weathering, while Transport moves them to other places. Sedimentation occurs when the transport agents lose energy, depositing the sediments in horizontal layers.
Diagenesis transforms loose sediments into compact rocks, involving: Compaction, which compresses the grains by the accumulation of the weight of the sediments, and Cementation, where substances fill the spaces between the grains, forming a consolidated rock.

About 75% of the Earth's surface is covered by sedimentary rocks, which represent only 6% of the total rocks. These rocks originate from sediments resulting from the fragmentation or dissolution of other rocks, including small rock grains and remains of living beings, such as shells, or from substances dissolved in water. The deposition and compaction of these sediments form consolidated sedimentary rocks, held together by cement.

Action of Living Beings - The modification and fragmentation of rocks can be caused by living organisms. An example is the growth of plant roots, which, when developing in rock crevices, contribute to the disintegration of materials.

Water, in its liquid and solid (ice) states, plays a central role in the transformation of geological landscapes. It reacts with rocks and can alter their minerals, while ice also plays a role in the fragmentation of rocks; When freezing in the fissures, the water expands its volume, putting pressure on the rock mass and causing it to break into blocks. Furthermore, water acts as a transport agent, carrying debris resulting from the erosion of rocks by rivers or glaciers over considerable distances.

All geological landscapes on Earth, whether composed of magnetic, metamorphic or sedimentary rocks, are continually subject to transformation by the action of climate, including water and wind, as well as the influence of living beings. These agents cause changes and wear in rocks, resulting in the formation of fragments and substances that are transported and deposited, contributing to the creation of new sedimentary rocks.

Rocks are composed of natural clusters of one or more minerals. Unlike organic matter, where elements, such as carbon, oxygen, hydrogen, calcium, iron or fluorine, are organized in a geometric and regular way, forming crystalline structures, this arrangement is only possible in solids. Any liquid substance, whether of biological origin (from living beings) or synthetic, cannot be classified as mineral.

In addition to the effervescent acid reaction, which is valuable in identifying calcite, there are other properties of certain minerals that are easily tested. Magnetite is a magnetic mineral, halite is salty, and sulfur has a distinctive odor. Identifying minerals in a rock is not always possible with hand samples, as the crystals may not be visible to the naked eye. In these situations, whenever mineral study requires it, it is necessary to allow light to pass through and conduct observations under a microscope.

Minerals can be identified through simple tests that evaluate characteristics such as color, brightness, trace, hardness, cleavage and reaction with acids. Color, although observable, is of little use in identification, as a mineral can have different colors. The shine can be metallic or non-metallic, depending on the light reflection. The trace refers to the color of the powder left by the mineral when it scratches a surface. Hardness, measured by the Mohs scale, indicates resistance to scratching, with harder minerals scratching softer ones. Cleavage, a mineral exhibits cleavage when it breaks, under the action of a force, along well-defined plane surfaces. Reaction with acids refers to the ability of some minerals to react with acids, producing effervescence. For example, calcite reacts with acid, releasing bubbles of carbon dioxide.

Minerals are solid, natural and inorganic substances, characterized by a crystalline arrangement and defined chemical composition. Differentiating themselves from organic materials, these compounds have particles organized in crystalline structures. Although there are more than four thousand known minerals, only about thirty are common. The presence of these minerals is essential in the manufacture of a variety of objects and products, contributing significantly to scientific and economic sectors, such as gold, tungsten, copper, zinc and lithium.

Magmatic landscapes formed by granite rocks are common in the North and Central regions of the continent. In contrast, the areas of the Madeira and Azores archipelagos are predominantly dominated by landscapes with basalt rocks. In the North, Center, Alentejo and interior regions of the Algarve, it is possible to find metamorphic landscapes. Sedimentary landscapes cover approximately a third of the territory, especially in the areas of the Center, Lisbon and Tagus Valley, and Algarve.

Geological landscape is the scenario formed in extensions of territory where one or more types of rocks predominate, giving them distinct characteristics, such as relief, soil quality, water courses and the distribution of life. Despite the wide variety, all of these landscapes are based on one or more of the three basic types of existing rocks: magmatic rocks (exemplified by granite and basalt), sedimentary rocks (such as limestone and sandstone) and metamorphic rocks (such as marble and schist). .