minerals

MINERALS

Definition of Mineral

  • A mineral is a naturally occurring, inorganic solid.

  • It has a specific chemical composition and a definite crystalline structure.

General Characteristics of Minerals

1. Naturally Occurring

  • Real diamonds vs. synthetic diamonds.

  • Examples include:

    • Diamond

    • Topaz

2. Inorganic

  • Minerals cannot be formed from materials that were once part of a living organism.

3. Solid

  • Minerals have a definite volume and shape, and they exist in a solid state.

4. Definite Chemical Composition

  • Minerals always contain specific elements in definite proportions:

    • Example: Na + Cl = NaCl (Salt)

    • Example: Si + O₂ = SiO₂ (Quartz)

5. Ordered Internal Structure

  • Atoms in a mineral are arranged in a systematic and repeating pattern.

  • Example: Halite has sodium (Na) and chlorine (Cl) in a cubic arrangement.

Crystalline vs. Amorphous Solids

  • Crystalline Solid: Atoms vibrate in place in a fixed pattern.

  • Amorphous Solid: Atoms are arranged randomly without a systematic pattern.

Mineral Classes

  • Minerals are classified based on the dominant anion:

Silicates

  • Contain silicate anions (SiO₂⁴⁻).

Oxides

  • Contain oxygen anions (O²⁻).

Sulfides

  • Minerals like pyrite and galena.

Sulfates

  • Contain sulfate anions (SO₄²⁻).

Halides

  • Contain halide ions (Cl⁻ or F⁻).

Carbonates

  • Contain carbonate ions (CO₃²⁻), such as malachite.

Native Elements

  • Examples: Copper, Gold, and Graphite.

Crystal Structure of Minerals

  • The atomic arrangement of minerals follows different crystal systems:

Crystal Systems Include:

  • Isometric

  • Tetragonal

  • Orthorhombic

  • Monoclinic

  • Triclinic

  • Hexagonal

  • Trigonal

  • The shape of a mineral depends on its crystal structure, determining how the mineral typically forms.

Physical Properties of Minerals

1. Crystal Form and Habit

  • Refers to the external shape of the mineral crystals.

2. Cleavage and Fracture

  • Cleavage: Breaks along smooth edges or layers.

    • Example: Muscovite (one direction), Feldspar (two directions), Halite (three directions).

  • Fracture: Breaks along uneven or irregular surfaces.

    • Example: Quartz shows fracture.

3. Luster

  • Refers to the way light reflects from the surface:

    • Metallic, Vitreous, Resinous, Pearly, Silky, Earthy.

4. Color and Streak

  • The color seen in minerals, and streak refers to the color of the mineral in powdered form.

5. Hardness

  • A measure of a mineral's resistance to being scratched, ranked on Mohs Hardness Scale:

    • 1 = Talc (softest), 10 = Diamond (hardest).

  • Common objects for comparison:

    • Fingernail (2.5), Copper Penny (3.5), Knife/Glass Plate (5.5).

6. Density (Specific Gravity)

  • Density = mass/volume.

  • Specific Gravity compares the density of the mineral with that of water.

  • Examples of dense minerals include galena, magnetite, and gold.