Mineralogy Overview and Classification

Study Notes

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.

Description

Dive into the fundamentals of mineralogy, exploring the composition, structure, and properties of minerals. This quiz covers the classification systems of minerals based on their chemical properties and occurrence. Understand the vast array of mineral groups and their significance in the Earth system.