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Introduction to minerals and analytical methods

Linda Kortelainen
Linda Kortelainen |

Contents

  1. Introduction
  2. Definition and Properties of Minerals
  3. Mineral Classification
  4. Analytical Methods for Minerals
  5. Summary and Conclusions
  6. References and Citations

 

1. Introduction

AI generated euhedral beryl

To understand how mineral compositions can be measured and analysed, it is key tounderstand first what minerals are. In short, minerals are essential natural materials found in various forms in soils and rocks. They form the basic structure of rocks and are vital for many industries, including mining, construction, and electronics. Here we will shortly go through the structure of minerals, properties, and analytical methods.

 

2. Definition and Properties of Minerals

Minerals are inorganic, crystalline substances with a well-defined chemical composition and a regular atomic structure. The basic unit of a crystalline structure is the unit cell, which, when repeated in three dimensions, forms the mineral's crystal. The classification of minerals is primarily based on their chemical composition and crystal structure.

Minerals have a specific crystal structure determined by the arrangement of atoms. This structure can be described using Bravais lattices, which are three-dimensional, periodically repeating grid models. There are a total of 14 Bravais lattice types, divided into seven main crystal systems:

Crystal System

Characteristics

Example Mineral

Structure Parameters

Triclinic

All edges and angles are different

Plagioclase

a ≠ b ≠ c, α ≠ β ≠ γ ≠ 90°

Monoclinic

One symmetry axis, angles not perpendicular

Gypsum

a ≠ b ≠ c, α = γ = 90°, β ≠ 90°

Orthorhombic

Three different-length, mutually perpendicular axes

Sulfur

a ≠ b ≠ c, α = β = γ = 90°

Trigonal

Threefold symmetrical structure

Quartz

a = b = c, α = β = γ ≠ 90°

Hexagonal

Sixfold symmetry

Beryl

a = b ≠ c, α = β = 90°, γ = 120°

Tetragonal

Two equal lengths and one different, all perpendicular

Rutile

a = b ≠ c, α = β = γ = 90°

Cubic

Three identical, perpendicular axes

Fluorite

a = b = c, α = β = γ = 90°

 

Triclinic

Monoclinic

Orthorhombic

Trigonal/Hexagonal

Tetragonal

Cubic

Image source: Wikipedia, https://en.wikipedia.org/wiki/Crystal_system

The crystal structure of a mineral affects its physical properties, such as hardness, density, and fracture characteristics. For example, cubic fluorite typically forms regular octahedral crystals, while orthorhombic olivine appears as elongated crystals. Quasicrystals, often found in metallic alloys, exhibit a quasi-periodic structure — long-range order without repeating unit cells — and can display symmetries forbidden in traditional crystals.

Miller Indices (hkl): Miller indices are a way to describe the atomic planes of a crystal in three-dimensional space. They are expressed in the form (hkl), where h, k, and l are integers that define where the plane intersects the main axes of the crystal structure.

Image source: Wikipedia, By DeepKling - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=12123337

Examples:

  • (100) represents a plane that intersects the x-axis at one unit cell length but does not intersect the y- or z-axes.
  • (010) intersects the y-axis but not the x- or z-axes.
  • (001) intersects the z-axis but not the x- or y-axes.

Miller indices are widely used in crystallography and mineral analysis, especially in X-ray diffraction (XRD), as they help to identify the structural planes of the crystal accurately.

Mineral Occurrence Forms: Minerals can appear in nature in different forms:

  • Euhedral Crystals – Perfectly developed crystal forms
  • Anhedral Crystals – Imperfectly developed crystals, such as in vein fillings
  • Pseudomorphs – Crystals that retain the original form but change their chemical composition

Additionally, minerals can be amorphous, lacking a regular crystal structure. Examples of amorphous minerals include opals and volcanic glass.

3. Mineral Classification

Minerals are classified based on their chemical composition into the following groups:

 

Mineral Group

Structural Unit / Formula

Well-Known Minerals

Typical Applications

Silicates

[SiO₄]⁴⁻ tetrahedrons

Quartz, Feldspar, Mica

Glass, ceramics, electronics

Oxides

Metal + O

Magnetite (Fe₃O₄), Hematite (Fe₂O₃)

Steel, pigments, batteries

Sulfides

Metal + S

Pyrite (FeS₂), Galena (PbS)

Metal ores, sulfuric acid production

Carbonates

CO₃²⁻

Calcite (CaCO₃), Dolomite (CaMg(CO₃)₂)

Cement, limestone, glass manufacturing

Sulfates

SO₄²⁻

Gypsum (CaSO₄·2H₂O)

Construction boards, fertilizers

Halides

F⁻, Cl⁻

Fluorite (CaF₂), Halite (NaCl)

Salt, optics

Phosphates

PO₄³⁻

Apatite (Ca₅(PO₄)₃(F,Cl,OH))

Fertilizers, lasers, toothpaste

Elements

Gold (Au), Graphite (C)

Electronics, jewelry, lubricants

4. Analytical Methods for Minerals

Mineral analysis is carried out using advanced methods that provide precise insights into the structural and chemical properties of minerals. Below are the primary techniques:

  • X-ray Diffraction (XRD):
    • Phase Identification: Distinguishing between different mineral phases, even when they are chemically similar.
    • Crystallinity Measurement: Assessing the degree of order in mineral samples.
    • Stress and Strain Analysis: Evaluating structural stress and deformation in minerals.
  • X-ray Fluorescence (XRF):
    • Elemental Composition Analysis: Rapidly identifying elements like iron, calcium, and silica.
    • Trace Element Detection: Pinpointing small quantities of rare earth elements or heavy metals.
    • Mining Exploration: Mapping ore deposits based on elemental concentrations.
  • Raman Spectroscopy:
    • Molecular Fingerprints: Unique spectral signatures for mineral identification.
    • Phase and Polymorph Identification: Distinguishing between different forms of the same mineral.
    • In-situ Analysis: Real-time measurements in harsh environments.
  • Synchrotron Measurements:
    • Sub-micron Resolution: Revealing fine-grained structures and defects in minerals.
    • 3D Tomography: Visualizing internal structures without sample destruction.
    • Trace Element Analysis: Detecting low-concentration elements with great sensitivity.

Synchrotron at Paul Scherrer Institute, Swiss Light Source. Picture: Linda Kortelainen

  • Scanning Electron Microscopy (SEM):
    • High-Resolution Imaging: Produces detailed surface images of mineral grains.
    • Mineral Texture Observation: Useful in understanding grain boundaries and microstructures.
    • Elemental Mapping: Often combined with EDS (Energy Dispersive X-ray Spectroscopy) for chemical composition.
  • Mineral Liberation Analysis (MLA):
    • Automated Mineralogy: Provides quantitative data on mineral abundance and associations.
    • Particle Tracking: Tracks liberation characteristics and size distributions in ore processing.
  • Laser-Induced Breakdown Spectroscopy (LIBS):
    • Rapid Elemental Analysis: Ablates small portions of the sample using laser pulses.
    • Minimal Sample Preparation: Ideal for field applications and real-time monitoring.
  • Inductively Coupled Plasma Mass Spectrometry (ICP-MS):
    • Ultra-trace Element Detection: Capable of measuring elements at parts-per-trillion levels.
    • Isotopic Analysis: Useful in geochronology and source tracing.

5. Summary and Conclusions

AI generated stibnite

Minerals are the foundational building blocks for many industrial applications, ranging from construction materials to advanced electronics. This white paper has presented a small exploration of mineral properties, classification, and analytical methods that allow for precise identification and application of minerals in various sectors.

Key insights from this analysis include:

  • Mineral Properties and Structures: Understanding crystal systems and chemical compositions is crucial for identifying mineral types and assessing their industrial value.
  • Advanced Analytical Methods: Techniques such as XRD, XRF, Raman Spectroscopy, and Synchrotron Measurements provide detailed information about mineral structures, phase compositions, and elemental distributions.
  • Industrial Applications of Analytical Methods: The use of XRD, XRF, and Raman Spectroscopy is critical in industries such as mining, construction, and electronics, where precise mineral characterization informs resource extraction, quality control, and material performance.

The future of mineral analysis is marked by automation, cloud integration, and sustainable extraction processes that minimize environmental impact. Continued innovation in analytical technologies will further enhance mineral utilization and drive forward industrial efficiency and environmental stewardship.

To support these advancements, a stronger connection between mineral characterization and industry application should be encouraged. Bridging these two areas will not only improve analysis accuracy but also enhance decision-making in mining exploration, material manufacturing, and environmental sustainability.

6. References

The following sources were referenced throughout this white paper to provide detailed insights and validate the presented information:

  • XRD, XRF, and Raman Spectroscopy in Mineral Analysis. Available at: Academia.edu
  • Applications of XRD in Mineral Characterization. Available at: MDPI
  • Raman Spectroscopy in Mineralogy and Geochemistry. Available at: Geoscience World
  • Industrial Applications of Minerals. Available at: Cambridge University Press
  • Digitalization in Mining and Resource Management. Available at: ScienceDirect
  • Synchrotron Techniques for High-Resolution Mineral Analysis. Available at: Springer Link
  • Cloud-based Analytical Methods for Geochemical Mapping. Available at: ResearchGate
  • Sustainability and Mineral Resource Optimization. Available at: Elsevier

 

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