BH

2-1 minerology questions - Tagged

Minerals

  • Definition: Natural occurring inorganic solids with an ordered internal molecular structure and definite chemical composition.

Rocks

  • Composed of minerals.

  • Approximately 5,000 minerals are known, with 50-100 new ones identified each year.

  • Example: Layered sedimentary rocks at the Grand Canyon, AZ.

Characteristics of Minerals

  • Criteria for a substance to be a mineral:

    • Naturally occurring.

    • Inorganic solid.

    • Ordered internal molecular structure (crystalline).

    • Definite chemical composition.

  • Definition of a rock: A solid aggregate or mass of minerals.

  • Examples: Beryl with microcline from Pakistan.

Exclusions from Mineral Definitions

  • Substances such as ivory, bone, seashells, and coral are NOT classified as minerals because they originate from living organisms.

  • Example: Carved ivory from Inuit cultures.

Atomic Structure of Minerals

  • Internal Arrangement of Atoms:

    • Crystalline structure is characterized by a highly ordered arrangement of atoms.

    • Contrast with glass, which lacks a specific pattern and doesn’t exhibit order.

Examples of Crystal Structures

  • Galena: Characterized by cubic structure leading to cubic cleavage and cubic crystal shape.

Composition of Minerals

  • Atomic Structure:

    • Nucleus contains protons (positively charged) and neutrons (neutral).

    • Electrons (negatively charged) surround the nucleus in electron shells.

Chemical Bonding in Minerals

  • Types of Bonds:

    • Ionic Bonding: Atoms gain or lose outermost electrons to form oppositely charged ions.

    • Example: Halite (NaCl).

    • Covalent Bonding: Atoms share electrons in a stronger bond than ionic.

Types of Chemical Bonds

  • Ionic Bonds arise from electrostatic attraction between charged ions.

  • Covalent Bonds involve sharing electrons, creating stronger attractions.

Physical Properties of Minerals

  • Crystal Form: Externally visible arrangement of atoms.

    • Example: Quartz crystals, pure silicon dioxide (SiO2).

  • Color: Highly variable and unreliable for identification.

  • Streak: The color of the powdered form of a mineral, useful for identification.

Hardness and Cleavage

  • Mohs Scale of Hardness: Ranks minerals based on their scratch resistance.

    • Diamond (10), Talc (1).

  • Cleavage: Described by number of planes and angles along which a mineral breaks.

  • Fracture: Irregular surfaces when minerals break.

Classification of Minerals

  • Rock-forming Minerals: Mainly silicates, accounting for 98% of the continental crust.

    • Silicates: Silicon and oxygen, forming the fundamental tetrahedral structure.

    • Examples: Quartz, Felspar.

Important Nonsilicate Groups

  • Nonsilicate Minerals: Include Oxides, Sulfides, Sulfates, Carbonates, and Phosphates.

    • Economic Importance: Minerals like Hematite (iron), Halite (salt), and Sphalerite (zinc).

    • Carbonates: Effervesce with dilute HCl, notable examples include Calcite and Dolomite.

Summary of Key Concepts

  • Minerals are characterized by their natural, inorganic, solid state, clear structure, and defined chemical makeup.

  • Their identification involves understanding physical properties like luster, color, and hardness, and mineral classification focuses on silicate versus nonsilicate types.