Minerals and Atomic Structure: Foundations for General Chemistry

Minerals and the Lithosphere

Composition of the Lithosphere

The lithosphere is primarily composed of rocks, which themselves are aggregates of minerals. Understanding the nature and classification of minerals is essential for both geology and general chemistry.

• Minerals are naturally occurring, inorganic, solid substances with a definite chemical composition and an ordered atomic structure.

• The term mineralogy derives from "mineral" and "-logy" (study of).

• Minerals are characterized by:

  • Natural occurrence

  • Inorganic origin

  • Solid state

  • Ordered internal structure (crystalline)

  • Definite chemical composition

• Rocks are collections of minerals.

Mineral Structure and Properties

Minerals can have the same chemical composition but different crystal structures, leading to distinct physical properties.

• Example: Graphite and diamond are both forms of carbon but differ in crystal structure and properties.

• At the molecular level, differences in chemical bonding and atomic arrangement result in variations in physical properties such as hardness, color, and cleavage.

Mineral Lattices

• Crystal lattice refers to the three-dimensional arrangement of atoms in a mineral.

• The lattice determines properties like hardness (e.g., diamond is hard, graphite is soft).

• Lattice structure also influences how crystals grow and break.

Example: Halite (NaCl)

• Halite forms cubic crystals due to its lattice structure.

• Cleavage occurs along planes of weakness in the lattice.

Mineral Identification

Criteria for Minerals

To be classified as a mineral, a substance must meet specific criteria:

• Natural occurrence

• Inorganic origin

• Solid state

• Ordered atomic structure

• Definite chemical composition

Examples and Non-Examples

• Minerals: Amethyst, cubic zirconia, halite, obsidian (with caveats)

• Not minerals: Sugar, ice (unless naturally occurring), baz (context needed)

• Additional info: Obsidian is a volcanic glass and lacks a crystalline structure, so it is not a true mineral by strict definition.

Composition and Structure of Minerals

Chemical Composition

There are approximately 4000 known minerals, each with a specific chemical composition and structure.

• Minerals are composed of elements.

• Some minerals consist of a single element (e.g., gold, sulfur).

• Most minerals are compounds of multiple elements.

• Elements combine in fixed ratios to form minerals.

Atomic Structure

Understanding atoms is fundamental to chemistry and mineralogy.

• Atom: The smallest unit of matter retaining chemical properties.

• Atoms consist of a nucleus (protons and neutrons) and electrons orbiting the nucleus.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

• Atomic number equals the number of protons.

• Atomic mass equals the sum of protons and neutrons.

• Isotopes are atoms of the same element with different numbers of neutrons.

Periodic Table

• Elements are organized by atomic number in the periodic table.

• Elements combine to form compounds and minerals.

Bonding and Mineral Formation

Types of Chemical Bonds

Minerals form through the combination of elements via chemical bonds.

• Ionic bonds: Transfer of electrons between atoms (e.g., NaCl).

• Covalent bonds: Sharing of electrons between atoms (e.g., diamond).

• Metallic bonds: Electrons are shared among many atoms (e.g., native metals).

Mineral Groups

Major Elements in Earth's Crust

Although thousands of minerals exist, only a few elements make up most of Earth's crust.

• Eight elements constitute about 98% of the crust:

  • Oxygen (O) – 46.6%

  • Silicon (Si) – 27.7%

  • Aluminum (Al) – 8.1%

  • Iron (Fe) – 5.0%

  • Calcium (Ca) – 3.6%

  • Sodium (Na) – 2.8%

  • Potassium (K) – 2.6%

  • Magnesium (Mg) – 2.1%

Classification of Minerals

Minerals are classified based on their dominant anion or anionic group.

• Silicates: Contain SiO4 tetrahedra; most abundant group.

• Oxides: Contain O2– anion.

• Sulfides: Contain S2– anion.

• Sulfates: Contain SO42– anion.

• Halides: Contain halogen anions (Cl–, F–, etc.).

• Carbonates: Contain CO32– anion.

• Phosphates: Contain PO43– anion.

• Native elements: Consist of a single element (e.g., gold, copper).

Properties Used to Identify Minerals

Physical Properties

Minerals are identified by their physical properties, which are determined by their chemical composition and crystal structure.

• Color: May vary due to impurities.

• Streak: Color of the powdered mineral.

• Luster: How a mineral reflects light (metallic, non-metallic).

• Hardness: Resistance to scratching; measured by Mohs scale.

• Crystal form: External shape of the mineral.

• Cleavage: Tendency to break along planes of weakness.

• Fracture: How a mineral breaks when cleavage is not present.

• Density (Specific gravity): Mass per unit volume.

• Other properties: Magnetism, reaction to acid, fluorescence, etc.

HTML Table: Major Elements in Earth's Crust

The following table summarizes the major elements found in Earth's crust and their approximate abundance:

Element	Symbol	Abundance (%)
Oxygen	O	46.6
Silicon	Si	27.7
Aluminum	Al	8.1
Iron	Fe	5.0
Calcium	Ca	3.6
Sodium	Na	2.8
Potassium	K	2.6
Magnesium	Mg	2.1

Key Equations and Concepts

• Atomic number: $Z = \text{number of protons}$

• Atomic mass: $A = \text{number of protons} + \text{number of neutrons}$

• Density: $\rho = \frac{m}{V}$

• General formula for silicate tetrahedron: $\text{SiO}_4^{4-}$

Summary

Minerals are the building blocks of rocks and are defined by their chemical composition and crystal structure. Their identification and classification rely on both chemical and physical properties, which are rooted in atomic structure and bonding. Understanding these concepts is foundational for both geology and general chemistry.

Additional info: Some context and definitions have been expanded for clarity and completeness.