Minerals

Minerals of the World

Objectives of Lecture

  • To learn about minerals and their features:

    • Structure

    • Composition

    • Properties

One Minute Challenge Questions

  • Can you think of the names of any minerals?

  • Can you think of any uses for minerals in your everyday life or in society?

What is a Mineral?

  • A mineral is defined as:

    • A naturally occurring substance found on Earth with the following characteristics:

    • Characteristic chemical composition

    • Ordered atomic structure

    • Specific physical properties

  • Importance:

    • Minerals are the building blocks of rocks!

Example of a Mineral: Halite

  • Commonly known as salt.

  • Characteristics:

    • Chemical composition: NaCl (Sodium Chloride)

    • Ordered atomic structure: Atoms bond in a cube shape.

    • Specific physical properties include:

    • Appearance: Clear/white

    • Solubility: Dissolves in water

    • Taste: Salty

    • Hardness: Soft (can be scratched with an iron nail)

Native Elements

  • Definition:

    • Elements from the periodic table that occur as uncombined natural substances within the Earth.

Most Common Minerals on Earth

  • Feldspar: Chemical formula: KAlSi<em>3O</em>8KAlSi<em>3O</em>8

  • Quartz: Chemical formula: SiO2SiO_2

Polymorphs

  • Definition:

    • Minerals that have the same chemical composition but different physical properties/structures.

  • Examples:

    • Graphite and diamond are both made of carbon but exhibit very different physical properties.

Mineral Crystal Shapes

  • Crystal shapes relate to how minerals are bonded.

  • Examples of mineral crystal shapes:

    • Pyrite

    • Mica

    • Quartz

More Examples of Mineral Structure

  • Hexagonal Quartz Crystal

  • Cubic Pyrite Crystal

  • Calcite Crystal

  • Trigonal Crystal

  • Pyritohedral Pyrite Crystal

  • Fluorite Cubic Crystals

Types of Bonding in Minerals

  • Ionic Bonding:

    • Definition: The transfer of electrons between atoms.

    • Example:

    • Sodium atom (Na) becomes sodium ion (Na+) when losing an electron.

    • Chlorine atom (Cl) becomes chloride ion (Cl-) upon gaining an electron.

    • Together they form sodium chloride (NaCl).

  • Covalent Bonding:

    • Definition: Electrons are shared between atoms.

    • Overview: Only one pair of electrons hold the nuclei together, while two pairs of electrons hold them closer and tighter.

  • Metallic Bonding:

    • Definition: Electrons move in a cloud around atoms, allowing for conductivity and malleability.

  • Van der Waals Bonding:

    • Definition: Weak bonds based on dipole attractions between atoms, similar to magnet attraction.

    • Example: Graphite exhibits both covalent and van der Waals bonding.

Mineraloids

  • Definition: Not technically minerals because they do not have an ordered atomic structure.

  • Examples:

    • Opal

    • Agate

Physical Properties of Minerals

  • Definition: The characteristics of minerals that encompass their appearance and behavior under different conditions.

  • Key characteristics include:

    • Luster: The way a mineral reflects light, categorized as metallic or non-metallic.

    • Color: Considered the least reliable characteristic; some minerals appear in various colors.

    • Hardness: The ability of a mineral to resist scratching, measured using Moh's Hardness Scale.

    • Magnetism: The ability of some minerals to produce magnetism.

    • Streak: The color of a mineral in powdered form, used for identification.

Moh's Hardness Scale

  • A scale that ranks minerals based on their hardness from 1 (softest) to 10 (hardest):

    • Talc: 1

    • Gypsum: 2

    • Calcite: 3

    • Fluorite: 4

    • Apatite: 5

    • Feldspar: 6

    • Quartz: 7

    • Topaz: 8

    • Corundum: 9

    • Diamond: 10

  • Common objects used as reference include:

    • Fingernail: 2.5

    • Copper penny: 3.5

    • Iron nail: 4.5

    • Glass: 5.5

    • Steel file: 6.5

    • Streak plate: 7.0

Testing Hardness

  • The process of determining a mineral's hardness by what other objects it can scratch or be scratched by.

Streak: Based on Color

  • Definition: The color of the mineral when powdered.

  • Note: Some minerals may be too hard to produce powder and instead scratch the streak plate.

Cleavage of Minerals

  • Definition: The ability of a mineral to break along specific planes according to its atomic structure.

  • Examples of cleavage:

    • Mica: Sheety cleavage

    • Galena: Cubic cleavage

    • Calcite: Rhombohedral cleavage

    • Fluorite: Octahedral cleavage

Fracture

  • Description: Some minerals do not cleave and instead exhibit fracturing patterns:

    • Example: Quartz displays conchoidal fracture.

Effervescence

  • Definition: The ability of a mineral to react when acid is applied.

  • Example: Calcite reacts with acid; this is a significant property since limestone is primarily composed of calcite. This reaction is responsible for cave formation in certain areas like Kentucky.

Effervescence: Acid Test on Calcite

  • An acid test is performed on calcite to demonstrate effervescence visually.

Fluorescence and Phosphorescence

  • Fluorescence: The ability of a mineral to glow when exposed to ultraviolet (UV) light due to high-energy light waves exciting the atoms, which release energy as light.

  • Phosphorescence: The ability of a mineral to continue glowing even after the UV light source is removed, similar to glow-in-the-dark materials.

Other Interesting Properties

  • Magnetism: Certain minerals can exhibit magnetic properties.

  • Piezoelectricity: The ability of some minerals to generate an electric charge under mechanical stress.

  • Refraction: The bending of light as it passes through a mineral, impacting how the mineral is perceived visually.

  • Taste: Some minerals, like halite, have distinct tastes when sampled (not recommended in practice).

  • Smell: Certain minerals may have unique odors.

Gemstones

  • Definition: Exceptional examples of minerals that possess:

    • A beautiful color or clarity

    • Rarity

    • Unusual processes of formation

Gemstone Forming Minerals

  • Examples:

    • Ruby: A variety of corundum

    • Beryl: Includes emerald as a highly valued form

    • Sapphire: Another variety of corundum

A Word About Testing and Identifying Minerals

  • Emphasis on various methods of mineral identification based on said properties and features previously discussed.

Summary

  • Minerals are the building blocks of rocks.

  • Key characteristics of minerals consist of:

    • Atomic structure

    • Chemical composition

    • Physical properties

  • These qualities can be used effectively to identify minerals.