Minerals and Rocks: A Comprehensive Overview
Minerals
Definition and Characteristics
Minerals are naturally occurring, inorganic solids with a definite chemical composition and an ordered internal crystalline structure. This structure, along with their chemical makeup, determines their unique physical properties. Minerals are homogeneous, meaning every piece of the same mineral exhibits the same properties.
Key Characteristics:
- Solid: Incompressible and maintains its shape regardless of its container, unlike liquids (incompressible, shape-changing) and gases (compressible, shape-changing).
- Inorganic: Not formed by carbon chains, distinguishing them from organic substances.
- Natural: Occurring in nature, not artificially created.
- Crystalline Internal Structure: Atoms, molecules, or ions are arranged in a three-dimensional repeating pattern.
- Fixed Chemical Composition: Representable by a chemical formula.
Amorphous Structures
Some substances resemble minerals but lack a crystalline structure. These are called amorphous. Their particles are arranged randomly, not in a regular pattern.
Crystals
A crystal is a single, continuous piece of a mineral bounded by flat surfaces (crystal faces). Crystal formation requires sufficient time, space, and undisturbed conditions.
Mineral Properties
Isomorphism: Two or more minerals with the same internal structure but different chemical compositions. Examples: Galena (lead sulfide) and Halite (sodium chloride).
Polymorphism: Two or more minerals with different internal structures but the same chemical composition. Examples: Diamond and Graphite (both carbon).
Hardness: Resistance to scratching, measured on the Mohs scale (1-10, with diamond being the hardest).
Luster: How a mineral reflects light (metallic, pearly, vitreous, dull, etc.).
Color: Determined by the absorption and reflection of light wavelengths.
Fracture: Breakage that produces irregular surfaces (e.g., conchoidal fracture in quartz).
Cleavage: Breakage along flat planes (e.g., lamellar cleavage in mica, cubic cleavage in galena).
Habit: The typical shape or form of a mineral crystal (e.g., prismatic, acicular, spherical).
Organoleptic Properties: Properties perceived by the senses, such as taste (e.g., salty halite) or smell (e.g., sulfur).
Birefringence: Splitting of light into two rays, creating a double image (e.g., calcite).
Magnetism: Attraction to magnets, common in minerals containing iron, cobalt, or nickel (e.g., magnetite).
Density: Mass per unit volume.
Streak: The color of the powdered mineral.
Rocks
Definition
A rock is a naturally occurring, coherent aggregate of one or more minerals and/or mineraloids.
Types of Rocks
Sedimentary Rocks
Formed from the diagenesis (compaction, dehydration, and cementation) of sediments.
- Detrital: Composed of rock fragments (clasts).
- Conglomerates: Clasts > 2 cm (rounded clasts) or breccias (angular clasts).
- Sandstones: Clasts 2 cm – 1/16 mm.
- Shales/Mudstones: Clasts
- Evaporites: Formed from the precipitation of salts as water evaporates (e.g., gypsum, halite).
- Carbonates: Composed of carbonate minerals (e.g., limestone, dolomite).
- Organogenic: Derived from organic remains (e.g., coal, oil).
Igneous Rocks
: they come from the consolidation of a magma. metamorphic rocks: metamorphic rocks come from preexistentes.Diagénesis: The process of formation of sedimentary rocks by compaction, dehydration and cementation of sediments.
Metamorphism: Changes in the structure of the rocks to be under heavy pressure and / or temperaturesWithout reaching fundirse.Clasificación of sedimentary rocks. Detrital sedimentary rocks: are formed by clasts (the clasts are debris, pieces of rocks), are classified according to size of clast: Conglomerates: clast than 2 cm. if the clasts are rounded conglomerate called, if called angular brechas.Areniscas: clasts of 2 cm – 1/16mm. Clays: 1/16mm juvenile clasts. Evaporitic sedimentary rocks: It forms by the precipitation of salts to evaporate the water in which they were dissolved. Examples: gypsum and halite or rock salt. Carbonate sedimentary rocks: are formed by carbonates, eg limestone and dolomites. Organogenic sedimentary rocks: are coal and oil. Coal: The process of decomposition and diagenesis of plant debris that is progressively enriched in carbon, with peat, lignite, coal and anthracite. Oil: from the decomposition and diagenesis of plankton. It consists of hydrocarbons, have gaseous components (methane, butane, propane), liquids (petrol, diesel, fuel, ..) and solids (tars, asphalt,).
Classification of magmatic rocks or volcanic magma ígneas.Rocas: come from the consolidation of the magma at the surface. Examples: basalt, andesite, obsidian, pumice. Plutonic magmatic rocks: they come from the consolidation of magma at depth. Examples: granite, syenite, gabbro. Plutonic magmatic rocks: they come from the consolidation of magma in cracks. Examples: pegmatite, aplite, porphyry, lamprophyres.