Understanding Minerals and Rocks: Formation and Types
Minerals: Definition and Characteristics
Minerals are solids formed by the accumulation of chemical elements in Earth’s crust. They must exhibit three characteristics: being natural, having an inorganic origin, and having a homogeneous chemical composition.
Types of Minerals
- Amorphous Minerals: Minerals whose components are disordered.
- Crystallized Minerals: Minerals whose components are ordered, resulting in a crystalline material.
- Silicates: A group of minerals containing mainly silicon and oxygen in their composition, the most abundant being quartz and feldspar.
Mineral Properties
- Color: The type of light a mineral reflects when illuminated by white light.
- Effervescence: The property of some minerals that generate an acid foam upon contact.
- Habit: The way in which crystals grow, eventually presenting different forms.
- Cleavage: The property of fracturing or breaking into fragments that have flat faces.
- Fracture: Minerals that have no cleavage do not shatter, giving rise to fragments with flat faces.
- Hardness: The resistance a mineral puts up to being scratched by another.
- Streak: The color of the dust that occurs when you scratch a mineral. It does not always match the color of the mineral.
- Luster: How a mineral reflects light; it can be metallic, vitreous, greasy, or dull.
- Magnetism: The property of minerals capable of attracting iron.
- Birefringence: The property of minerals that causes light to unfold into two images when passing through them.
Mohs Hardness Scale
Talc, Gypsum, Calcite, Fluorite, Apatite, Orthoclase, Quartz, Topaz, Corundum, Diamond.
Homogeneous Crystalline Aggregates
- Geodes: Crystals grow within a cavity.
- Druses: Crystals grow on a flat surface.
- Dendrites: The mineral grows on a surface, drawing branched forms, and can be mistaken for fossils.
- Twins: Appear when crystals collide as they grow.
Types of Rocks
- Sedimentary: Formed by the accumulation and compaction of sediment.
- Magmatic: Formed by the cooling of magma.
- Metamorphic: Formed in the interior of a volcano.
Sedimentary Rocks
The four types of sedimentary rocks are detrital, limestones, evaporites, and organic. Once materials are accumulated, there are two processes: compaction and cementation.
Formation of Limestone
- The accumulation of shells and skeletons of living organisms or their fragments.
- The precipitation of calcium carbonate from water that is in solution.
Formation of Evaporitic Rocks
In places where the climate is dry and hot and there are expanses of salt water, intense evaporation causes the precipitation of dissolved minerals, such as gypsum and salt.
Formation of Organic Rocks
- Coal: Comes from the accumulation of plant material, which is buried and subjected to high pressures and temperatures.
- Oil: Caused by the accumulation of microscopic particles of organic matter from marine plankton.
Magmatic Rocks
Magma is a mixture composed of silicate rocks, gases, and water vapor. Upon cooling, it results in magmatic rocks. Magmatic rocks can be extrusive or volcanic, plutonic or intrusive, or intermediate or philonian.
Metamorphic Rocks
Metamorphism is the set of changes in a rock subjected to high pressures and temperatures; the result is a metamorphic rock.
Types of Metamorphic Rocks
- Foliated: Formed by subjecting certain rocks, such as clays, to increased pressure.
- Non-foliated: The metamorphic aureole is the zone around the magma in which the temperature is elevated, and rocks found there are subject to change.
Limestone rocks are transformed into marble, and quartz-rich clays into quartzite.
The Rock Cycle
- Minerals break and disintegrate.
- Magmatic and volcanic rocks form.
- Rock fragments are transported, beaten, and reduced to smaller fragments.
- The sinking of the land surface favors the accumulation of sedimentary layers.
- The weight of the sediment layers transforms them into sedimentary rocks.
- The forces that compress the crust and produce high temperatures result in metamorphic rocks.