Mineralogy Overview and Classification

Mineralogy Overview

• Mineralogy is the scientific study of minerals, including their composition, structure, properties, occurrence, and origin.
• It examines the physical and chemical characteristics of minerals, determining their formation environments, and their relationships within the Earth system.
• It is closely related to other fields like petrology, geochemistry, and geophysics.

Minerals Classification

• Minerals are naturally occurring, inorganic solids with a definite chemical composition and a highly ordered atomic arrangement.
• Classification systems group minerals based on their chemical composition, structure, and physical properties.
• A common method of classification involves grouping minerals based on the anion (negatively charged ion) present in the mineral formula.
• Examples of major mineral groups include silicates, oxides, sulfides, sulfates, carbonates, halides, and native elements.
• Silicates are the most abundant group, comprising over 90% of the Earth's crust.

Mineral Properties

• Various properties are used to identify and describe minerals.
• Physical properties include:
  • Color: The visible color of the mineral.
  • Streak: The color of the mineral's powder.
  • Luster: The way light reflects off the mineral's surface (e.g., metallic, glassy, pearly).
  • Hardness: A measure of a mineral's resistance to scratching, using the Mohs Hardness Scale.
  • Cleavage: The tendency of a mineral to break along planes of weakness.
  • Fracture: The way a mineral breaks along irregular surfaces.
  • Specific gravity: The density of a mineral relative to the density of water.
  • Magnetism: Some minerals exhibit magnetic properties.
  • Taste: Some minerals have a particular taste (e.g., halite).
  • Transparency/Opacity: How much light passes through the mineral.
• Optical properties include:
  • Double refraction (in some minerals): A phenomenon where light is split into two rays when passing through certain crystals.
  • Fluorescence: Some minerals emit light when exposed to ultraviolet or other types of radiation.

Crystal Structures

• The arrangement of atoms in a mineral determines its crystal structure.
• Crystal structures are highly ordered and repetitive, forming characteristic shapes like cubes, prisms, or octahedrons.
• Crystal systems are classified based on the symmetry of their fundamental unit cell, yielding seven main systems. These are further subdivided into classes with particular symmetry elements.
• These structures influence the physical and chemical properties of the minerals through interactions between atoms.
• Defects (or imperfections) in the crystal structure can also impact these properties.

Properties of Minerals: Specific Examples

• Quartz (SiO₂): Typically exhibits a glassy luster, various colors, is hard (7 on the Mohs scale), and has a conchoidal fracture. It lacks cleavage.
• Feldspar (e.g., KAlSi₃O₈): Often exhibits a glassy luster, wide range of colors, hardness of 6-6.5, and good cleavage in two directions.
• Galena (PbS): Exhibits a metallic luster, is typically gray or lead-colored, has a hardness of 2.5, and good cubic cleavage.
• Halite (NaCl): Has a salty taste, is colorless or white in pure form, exhibits a glassy luster, has a hardness of 2, and is characterized by perfect cubic cleavage.
• Hematite (Fe₂O₃): Can exhibit a reddish-brown or black color, possesses a metallic luster, hardness of 5.5-6.5, and weak cleavage.