Minerals, Crystal Structures, and Chilean Copper Mining

Mineral Formation Processes

• Oxide Formation: Oxygen combines with other elements to form compounds such as oxides, including FeO, Na₂O, Al₂O₃, MgO, and SiO₂.

Understanding Minerals

Minerals are substances in solid form, made up of an element or chemical compound, formed through natural processes. They are typically found in deposits within rocks, appearing as filled fissures or cracks.

Common Mineral Examples

• KAl₂(AlSi₃)O₁₀(OH)₂ (Mica)
• KAlSi₃O₈ (Feldspar)
• SiO₂ (Quartz)

Primary Minerals

These minerals are part of original deposits. Pyrite (FeS₂) is a primary mineral that resembles gold in color and brightness.

Secondary Minerals

These are minerals that have formed from chemical reactions of primary minerals. Anglesite (PbSO₄) is a secondary mineral that forms from Galena (PbS), a primary mineral.

What is Mineralogy?

Mineralogy is the science that studies the physical and chemical properties of minerals.

Mineral Crystal Structures

Crystalline Solids Defined

In crystalline solids, particles are grouped in an orderly and regular manner in all three dimensions of space, forming defined shapes. Most existing solid materials on Earth are crystals, such as quartz (SiO₂).

Amorphous Solids Explained

Amorphous solids have particles arranged randomly, resembling liquids in structure, and are shapeless. Exceptions to crystalline solids include amorphous solids like volcanic rocks.

Mineral Crystallinity

Minerals are crystalline solids, meaning their particles are arranged in space according to precise, regular structures.

The Mineral Unit Cell

Crystals are made of a fundamental unit called a unit cell, which is repeated indefinitely in three dimensions of space.

Major Crystal Systems

• Cubic: Pyrite
• Tetragonal: Cassiterite
• Trigonal: Siderite
• Hexagonal: Beryl
• Orthorhombic: Sulfur
• Monoclinic: Gypsum
• Triclinic: Axinite

Physical Properties of Minerals

The physical properties of minerals are related to their internal structure, including hardness, fracture, and exfoliation.

Mohs Hardness Scale

The Austrian mineralogist Friedrich Mohs established in 1812 a hardness scale that is still current, known as the Mohs hardness scale.

Hardness Definition

Hardness: The resistance offered by the smooth surface of a mineral to being scratched.

Fracture Characteristics

Fracture: The manner in which a mineral breaks when struck (e.g., chips, irregular, or conchoidal).

Exfoliation Tendency

Exfoliation: The tendency of a mineral to split along one or more planes when struck.

Chile's Vital Mining Industry

Copper Production Dominance

Approximately 70% of Chile's mining production corresponds to copper.

Major Mining Companies in Chile

• State-owned: Corporación Nacional del Cobre (Codelco), through its five divisions: Codelco Norte, Salvador, Ventanas, Andina, and El Teniente. Codelco is the largest producer of copper in the world and the second largest producer of molybdenum.
• Private: Minera Escondida Ltda., MP and Candelaria, Minera Mantos Blancos S.A., and Minera Doña Inés de Collahuasi, among others.

Other Significant Mineral Exports

In addition to copper and molybdenum, Chile exports gold, silver, iron, nitrate, and iodine. The industry's successful production of lithium and rhenium minerals is also noteworthy.

Copper Metallurgy in Chile

Defining Commercial Ore

When a mineral has a metallic content suitable for market, it is called an ore.

Chilean Copper Ore Grade Example

Chilean copper ore, for example, often has a high metal content: typically 1.5% copper and 0.03% molybdenum.

Understanding Ore Grade

Any metal content of commercial interest in an ore is called its grade, expressed as a percentage.

Properties of Copper Metal

Physical Properties of Copper

• Reddish in color with a metallic luster; extremely ductile and malleable.
• Crystallizes in the cubic system; has a hardness of 2-3 on the Mohs scale.
• After silver, it is the best conductor of electricity and heat.

Chemical Properties of Copper

• Oxidizes slowly in air, forming a green oxide layer that protects it from further corrosion.
• Resistant to clean water and many chemicals; however, oxidizing acids like nitric acid corrode it easily.
• Used in various alloys, such as brass (Cu-Zn), bronze (Cu-Sn), and alpaca (Cu-Ni-Zn).
• Copper is found combined with oxygen or sulfur, forming oxidized copper minerals and sulfides, respectively.