Minerals: Building Blocks of Earth

Study Notes

Minerals: Building Blocks of Earth

Minerals are the fundamental components of rocks, soil, and Earth's mantle.
Mineralogists use a set of criteria to identify and classify minerals.

Characteristics of Minerals

Naturally Occurring: Formed by Earth's natural processes.
Inorganic: Product of Earth's physical processes.
Homogeneous Solid: Has a defined volume and rigid shape.
Definite Chemical Composition: Represented by a chemical formula.
Orderly Crystalline Structure: Atoms are arranged in a regular, repeating pattern.

Physical Properties of Minerals

Color: Can vary due to surface conditions, but can be a unique identifier for some minerals.
Streak: The color of a mineral's powder, often a more reliable identifier than color.
Luster: How light reflects off a mineral's surface:
- Metallic: Opaque, reflective like polished metal.
- Non-metallic: Can be glassy, diamond-like, resinous, silky, pearly, dull, greasy, etc.
Hardness: Resistance to scratching, measured on Mohs Hardness Scale:
- Developed by Friedrich Mohs in 1812.
- Compares minerals from very soft (talc) to very hard (diamond).
Cleavage: Tendency to break along smooth, flat surfaces due to inherent weaknesses in atomic bonding.
Fracture: Irregular, non-planar breakage pattern in minerals that don't cleave.
Crystalline Habit: Overall shape or growth pattern of a mineral:
- Equant: Three dimensions are roughly equal (e.g., garnet).
- Elongate: Prismatic, thicker than needle-like (e.g., Indicolite).
- Platy: Flattened and thin (e.g., Wulfenite).
Magnetism: Some minerals are attracted to magnets, with magnetite being the most common magnetic mineral.
Reaction with Acid: Some minerals, especially carbonates, react visibly with dilute hydrochloric acid (HCl), releasing carbon dioxide.
Striation: Very thin, parallel grooves on cleavage surfaces, best observed with a hand lens.
Specific Gravity: The weight of a mineral relative to the same volume of water. Most silicates have a specific gravity of 2.6 to 3.4, while ore minerals are usually heavier (5 to 8).
Taste, Odor, Feel: Some minerals have distinctive properties, such as a salty taste (halite), sulfurous odor (some sulfides), or slippery feel (talc).

Chemical Properties of Minerals

Dana System: A classification scheme developed by James Dwight Dana that groups minerals based on their chemical composition and atomic structure.
- Divides minerals into eight classes:
  - Native Elements: Uncombined, naturally occurring forms like metals, semimetals, and nonmetals.
  - Silicates: The largest group of minerals.
  - Oxides: Compounds of oxygen and another element.
  - Sulfides: Compounds of sulfur and another element.
  - Sulfates: Compounds containing sulfur and oxygen.
  - Halides: Compounds of a halogen (e.g., chlorine, fluorine) and another element.
  - Carbonates: Compounds containing carbon and oxygen.
  - Phosphates: Compounds containing phosphorus and oxygen.
  - Mineraloids: Substances lacking a true crystalline structure (e.g., opal).