Rocks, Minerals, and Air Masses: A Geological Overview
Rocks and Minerals
Rocks
Rocks are associations of one or more minerals. They are natural, inorganic, heterogeneous materials with variable chemical compositions and no specific geometry, formed by geological processes.
Minerals
Minerals are natural, inorganic, homogeneous, solid or liquid elements or compounds with a constant chemical composition. They generally adopt a particular geometric shape as a result of chemical processes.
Rock Classification
Igneous Rocks
Igneous rocks result from the consolidation of magma.
- Intrusive Igneous Rocks: Formed beneath the Earth’s surface.
- Extrusive Igneous Rocks: Volcanic rocks crystallized on the Earth’s surface.
Sedimentary Rocks
Sedimentary rocks are formed by the consolidation of sediment.
- Clastic Rocks: Their structure clearly shows that the materials within them come from the fragmentation of other rocks.
- Non-Clastic Rocks: Divided into organic (from accumulated plant and animal remains) and chemical (formed by precipitation of substances in solutions).
Metamorphic Rocks
Metamorphic rocks originate from other rocks that have undergone a transformation beneath the Earth’s surface.
- Foliated: Exhibit schistose structures.
- Non-Foliated: Do not have schistose structures.
Mineral Classification
Essential Minerals
Essential minerals are indispensable to a rock’s composition; their absence would change the rock type.
Accessory Minerals
Accessory minerals occur in small amounts and don’t influence the rock’s character. If present in significant quantities, they are called characteristic minerals.
Primary Minerals
Primary minerals (also called syngenetic minerals) crystallize from magma or magmatic water, forming simultaneously with the igneous rock.
Secondary Minerals
Secondary minerals result from the alteration of primary minerals in the Earth’s crust’s superficial zones.
Mineral Uses
- Quartz (SiO2): Jewelry, electronics (watches).
- Graphite (C): Lubricants, pencils, paint.
- Halite (NaCl): Food, chemical manufacturing.
- Gypsum (CaSO4ยท2H2O): Building materials.
- Diamond (C): Cutting, polishing, drilling, jewelry.
Mineral Properties
Physical properties used to identify minerals include: color, brightness, clarity, thermoluminescence, triboluminescence, fluorescence, phosphorescence, and exfoliation.
Air Masses
Air masses are uniform units of air in terms of temperature and moisture content. They can cover vast areas and move together. There are approximately 20 source regions for air masses, classified as polar, tropical, maritime, or continental.
- Continental Polar Air Mass: Cold and dry.
- Maritime Polar Air Mass: Relatively warm and wet in winter, cool in summer.
- Continental Tropical Air Mass: Hot and dry.
- Maritime Tropical Air Mass: Moist and relatively cool.
Convection
Convection is the process of air rising and falling due to temperature differences. For example, warm air rises up a sun-scorched mountain during the day, while cool mountain air descends to the heated valley at night. Convection transfers heat from hot to cold areas.
Hadley Cell
Air rising at the equator doesn’t reach the poles; most descends back to the Earth’s surface around 30 degrees latitude, forming the Hadley cell.
Air Fronts
When two air masses of different densities and temperatures meet, they form a front, a sloping discontinuity surface. There are three types of fronts:
- Cold Front: Cold air moves under warm air, forcing it upwards. Characterized by lower temperatures, wind shifts, and sudden showers. The most common type of front.
- Warm Front: Warm air moves over cold air. The cold air remains in contact with the ground, and the rising warm air cools adiabatically, forming clouds and prolonged precipitation.
- Occluded Front: Forms when two cold air masses trap a warm air mass between them, lifting the warm air off the ground. This occurs in the final stage of a cyclone.
Planetary Winds
Large-scale wind patterns on Earth’s surface include trade winds, westerlies, and polar easterlies.