Minerals GEOL 1340

Minerals Overview

  • Course Information: GEOL 1340; provided for instructional viewing only.

  • Source: Paleontological Research Institution.

What is a Mineral?

  • Definition: A mineral is a naturally occurring, inorganic, crystalline solid that has a specific chemical composition.

    • Reference: Marshak, 2015, Fig. 5-2.

Formation of Minerals

  • How do minerals form? The formation of minerals can occur through several processes:

    • Solidification from Melt: This involves the cooling and solidification of molten rock materials.

    • Precipitation from Solution: Minerals can form from a solution as the solute precipitates out under certain conditions.

    • Bioprecipitation: Biological processes contribute to mineral formation.

    • Direct Precipitation from Vapor: Minerals can form when vapor cools and concentrate.

    • Solid-State Diffusion: During this process, atoms or ions move within the solid crystalline structure leading to changes.

Understanding Crystalline Structures

  • What Does it Mean to be Crystalline? A crystalline structure is characterized by:

    • Regular: A consistent arrangement of atoms or ions.

    • Repeating: The structure is periodic, repeating throughout the mineral.

    • Orderly: There is a specific geometric arrangement.

    • Reference: Marshak, Fig. 5-3a.

Exploration of Mineral Properties

Liquids and Glass as Minerals

  • Why aren't liquids minerals?: Liquids lack a fixed crystalline structure.

  • Why isn't glass a mineral?: Glass is amorphous and does not have a regular internal structure.

  • Is ice a mineral?: Ice qualifies as a mineral as it has a crystalline structure.

Example of Orderly Crystal Structure

  • Sodium Chloride (NaCl): Commonly known as salt.

    • Structure: Sodium (Na⁺) and Chloride (Cl⁻) ions are bonded in a cubic lattice via ionic bonds.

    • Representation: Models such as ball-and-stick and geometric figures can depict these structures.

    • Reference: Marshak, Fig. 5.8.

Types of Bonds in Minerals

  • Ionic Bonds: Electrons are transferred from one atom to another.

  • Covalent Bonds: Electrons are shared between atoms.

  • Metallic Bonds: Electrons move freely across the structure.

  • Van der Waals Forces: Electrostatic interactions that can hold materials together.

    • Examples: Diamond and Graphite.

    • Reference: Marshak, Fig. 5-10a/b.

Chemical Composition of Minerals

  • Specific Chemical Composition: Refers to the definite set of elements and proportions that constitute a mineral.

  • Abundant Elements in Earth's Crust: The eight most abundant elements account for 98% of the crust's weight:

    1. Oxygen (O) – 47%

    2. Silicon (Si) – 28%

    3. Aluminum (Al) – 8%

    4. Iron (Fe) – 5%

    5. Calcium (Ca) – 4%

    6. Sodium (Na) – 3%

    7. Potassium (K) – 3%

    8. Magnesium (Mg) – 2%

  • Significance of Silicates: Most minerals are Silicates, which represent more than 90% of the Earth's crust due to the abundance of Silicon and Oxygen.

    • Weight Percentage Reference: For details see Marshak, Table A.1, p. 151.

Silicate Minerals Structure

  • Silicate Tetrahedra: The fundamental building block is the silicate tetrahedron (SiO44−SiO_4^{4-}).

    • Implications of Bonding: Strong bonding within the tetrahedron influences mineral properties.

    • Arrangement of Tetrahedra: Defines major structural types:

    • Isolated: Tetrahedra do not share oxygen atoms.

    • Single-chain: Tetrahedra share two oxygen atoms.

    • Double-chain: Tetrahedra share two or three oxygen atoms.

    • Sheet Structure: Tetrahedra share three oxygen atoms forming sheets.

    • Framework Structure: Tetrahedra share all four oxygen atoms.

    • Reference: Marshak, Fig. 5-16.

Other Major Mineral Classes

  • Non-Silicates: Classified primarily by their anion or dominant chemical ions.

    • Common Classes:

    • Carbonates: CO32−CO_3^{2-}

    • Sulphides: S2−S^{2-}

    • Sulfates: SO42−SO_4^{2-}

    • Oxides: O2−O^{2-}, O2O_2

    • Phosphates: PO43−PO_4^{3-}

    • Chlorides: Cl−Cl^{-}

Carbonates

  • Major Examples:

    • Calcite (CaCO₃): Most common non-silicate mineral.

    • Dolomite (CaMg(CO₃)₂): Common in sedimentary rocks like limestone and marble.

  • Source: Indiana Geological Survey, Wikimedia Commons.

Sulphides

  • Major Examples:

    • Pyrite (FeS₂)

    • Chalcopyrite (CuFeS₂)

    • Galena (PbS)

    • Sphalerite (ZnS)

    • Reference: Marshak, Fig. 5-12c.

Sulfates

  • Major Example:

    • Gypsum (CaSO₄·2H₂O)

Chlorides

  • Major Examples:

    • Halite (NaCl)

    • Sylvite (KCl)

Native Elements

  • Includes:

    • Silver (Ag)

    • Sulfur (S)

    • Gold (Au)

    • Copper (Cu)

    • Graphite (C)

    • Diamond (C)

Mohs Scale of Mineral Hardness

  • Scale Overview:

    1. Talc

    2. Gypsum

    3. Calcite

    4. Fluorite

    5. Apatite

    6. Feldspar

    7. Quartz

    8. Topaz

    9. Corundum

    10. Diamond

  • Resource: GeologyIn.com.

Physical Properties of Minerals

  • Reflective Characteristics:

    • Colour

    • Streak

    • Hardness

    • Specific gravity

    • Crystal form

    • Cleavage (preferred directions of breakage)

    • Other properties based on atomic structure and bonding.

Key Questions for Understanding

  • What are the eight most abundant elements in Earth’s crust?

  • What is their collective weight percentage in the crust?

  • What are the top three elements and their percentages?

  • State the three conditions that define a mineral.

  • How are atoms held in place within a crystalline structure? (Types of bonding?)

  • List at least three methods by which minerals can form.

  • Define “rock-forming minerals” and their significance.