2-1 minerology questions - Tagged

Minerals: Overview

• Definition: Building blocks of rocks.

• Known minerals: Approximately 5,000, with 50-100 new minerals identified each year.

Characteristics of Minerals

• Key Definitions:

  • Mineral:

    • Naturally occurring

    • Inorganic solid

    • Ordered internal molecular structure

    • Definite chemical composition

  • Rock:

    • Solid aggregate or mass of minerals.

• Examples: Beryl with microcline from Pakistan.

What are NOT Minerals?

• Examples of materials that are NOT minerals include ivory, bone, seashells, coral, and petrified wood.

Atomic Structure and Crystalline Arrangement

• Crystalline Structure:

  • Mineral atoms are arranged in an orderly framework known as a crystal lattice.

  • Glass has a random arrangement, lacking a specific pattern, unlike quartz crystals.

• Galena Atomic Structure:

  • Cubic structure allows for cubic cleavage and distinctive crystal shape.

Mineral Classification by Bonding

• Ionic Bonding:

  • Involves the transfer of electrons to form oppositely charged ions.

  • Example: Halite (NaCl) shows ionic bonding via electron transfer.

• Covalent Bonding:

  • Involves sharing of electrons between atoms; generally stronger than ionic bonds.

Mineral Structure and Properties

• Polymorphs:

  • Example: Diamond and graphite; both are forms of carbon but have different structures and properties.

    • Diamond: Strong covalent bonds in a 3-D grid.

    • Graphite: 2-D sheets with weak Van der Waals bonds.

Physical Properties of Minerals

• Crystal Form: External expression of atomic arrangement, often competing for space.

• Luster Types:

  • Metallic

  • Nonmetallic

    • Examples include Pearly, Vitreous, Resinous, Silky, Dull, Earthy.

• Color:

  • Highly variable and unreliable for identification; gemstones often exhibit exotic colors.

• Streak:

  • Color of a mineral in powdered form, helpful for distinguishing between forms of the same mineral.

• Hardness:

  • Measured by Mohs scale, which assesses resistance to scratching.

    • Mohs Scale:

      • Diamond (10), Corundum (9), Topaz (8), Quartz (7), etc.

• Cleavage:

  • Planes of weak bonding leading to flat, shiny surfaces; described by the number of planes and angles.

• Fracture Types:

  • Smooth, Rough, Splintery, Irregular, Conchoidal.

Classifications of Minerals

• Rock-forming minerals: Comprise >98% of continental crust; important for understanding Earth’s structure.

• Silicates:

  • Most abundant mineral group, characterized by the silicon-oxygen tetrahedron.

  • Various structures (e.g., isolated tetrahedra, ring structures, chains, sheets).

Common Silicate Minerals

• Olivine: High-temperature Fe-Mg silicate.

• Pyroxene Group: Single-chain silicates with distinctive cleavages.

• Amphibole Group: Double-chain silicates with characteristic angles.

• Mica Group: Sheet structures with one direction of cleavage (Biotite and Muscovite).

• Feldspar Group: Most common, characterized by a 3-D framework.

Important Nonsilicate Minerals

• Carbonates:

  • Includes limestone, dolostone; effervesce with dilute HCl (example: Calcite).

• Economic Value:

  • Varieties like Hematite (iron ore), Halite (salt), Sphalerite (zinc ore), Native Copper (copper).

Questions Review

• Which common mineral effervesces with dilute HCl?

• Write down the key characteristics defining a mineral.