Rocks and Minerals: Composition, Types, and Uses

Rock Formation and Classification

Rocks are natural aggregates consisting of one or more minerals. Minerals are natural solids with a crystalline structure. Rocks vary in composition and mineral proportions. The texture of a rock, such as grainy or banded, is its superficial aspect. The mineral association, which gives us its chemical composition, is the set of minerals that form the rock. The age of a rock can be determined through various methods, including analyzing fossils found within or nearby.

Igneous Rocks

Igneous rocks form from magma, which is molten rock found beneath the Earth’s surface. Magma’s characteristics, such as chemical composition, temperature, density, crystallization process, and location, influence the type of igneous rock formed.

Types of Igneous Rocks

• Exterior or Volcanic rocks: Found on the Earth’s surface, such as basalt.
• Intrusive rocks: Formed inside the Earth’s crust.
• Plutonic rocks: Like granite, formed by slow cooling at great depths, resulting in large crystals.
• Filonian rocks: Such as porphyry, formed at average depths with quicker cooling than plutonic rocks, resulting in average-sized crystals.

Metamorphic Rocks

Metamorphic rocks are formed when existing rocks are transformed by extreme pressure and temperature without changing their solid state. There are two main types:

Types of Metamorphism

• Contact metamorphism: Localized, affecting a small area, such as marble from limestone.
• Regional metamorphism: Affecting large areas, thousands of square kilometers.

The Rock Cycle

The rock cycle is a continuous set of processes that transform rocks within the Earth’s crust. These processes include:

• Erosion (blue arrows): Destruction of rocks.
• Deformation (green arrows): Changes due to temperature and pressure.
• Fusion (red arrows): High temperatures transform rocks into magma.

Rocks as a Resource

Rocks are used as both energy and non-energy resources.

Energy Resources

Oil is an organic rock, refined into petrol, diesel, kerosene, paraffin, tar, and plastics.

Non-Energy Resources

Metallic resources include bauxite, the source of aluminum. Non-metallic resources include rocks used in building, such as marble, and cement, made from limestone and sandstone.

Mineral Composition and Properties

Mineral matter refers to the inorganic substances that make up the Earth’s crust, including rocks and minerals. The Earth’s crust is primarily composed of oxygen (O) and silicon (Si). Silicates, formed by silicon and oxygen, are the most abundant group of minerals.

Amorphous vs. Crystalline Matter

• Amorphous matter: Atoms are randomly distributed, like in gases, liquids, and some solids like bauxite.
• Crystalline matter: Atoms are perfectly ordered, forming crystals like quartz and diamonds.

A mineral is a natural, solid, homogenous, uniform, crystalline substance.

Characteristics of Minerals

• Solid: Minerals are always solid.
• Natural: Found in nature.
• Homogenous: Always the same composition.
• Uniform: Same properties throughout.
• Crystalline: Atoms are spatially ordered.

The chemical properties of a mineral are due to its composition, such as its capacity to dissolve in water or its taste, like the salty taste of halite.

Physical Properties of Minerals

• Tenacity: Resistance to breaking.
• Malleability: Ability to be extended into sheets.
• Ductility: Ability to be stretched into threads.
• Conductivity: Capacity to conduct electricity, magnetism, etc.

Examples of Minerals

• Calcedonium: A sedimentary mineral used in jewelry.
• Halite: A sedimentary mineral, common salt.
• Quartz: A silicate, transparent with hexagonal crystals, used in watches.
• Graphite: A metamorphic mineral, used in pencils, made of pure carbon.
• Talc: A metamorphic mineral, very soft, used for personal hygiene.