Gemstone Articles

How Are Minerals Classified: The Essential Guide

by Alison Cornford-Matheson on Feb 11, 2026

Whether you are a student, geology enthusiast, hobbyist, or professional, understanding how minerals are classified is essential for identifying, studying, and appreciating Earth's building blocks. Minerals are primarily classified by their chemical composition and internal crystal structure. This guide explains how minerals are classified by their chemical composition, crystal structure, and physical properties. Knowing how minerals are grouped is crucial not only for academic study but also for practical applications in industry, mining, and collecting. By learning the main categories—such as silicates, carbonates, oxides, sulphides, sulphates, halides, phosphates, and native elements—you will gain a deeper appreciation for the diversity and significance of minerals in our world.

Key Takeaways

Minerals are classified based on their crystalline structure, inorganic nature, natural formation, and chemical composition, leading to distinct groups such as silicates and carbonates.
Minerals are primarily classified by their chemical composition and internal crystal structure.
Major classifications of minerals include silicates, carbonates, oxides, sulphides, sulphates, halides, phosphates, and native elements.
The eight elements—oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, and potassium—are fundamental to mineral formation and classification, as they make up the majority of the Earth's crust and influence mineral chemistry and structure.
The seven crystal systems categorize minerals based on their geometric properties and symmetry, which influence the physical characteristics essential to classification.
Physical properties like hardness, lustre, and cleavage are critical in mineral identification. They help geologists and mineralogists accurately categorize and study minerals.
Mineralogists use a variety of physical and optical properties to help identify minerals without special equipment.

Understanding Minerals

Minerals are naturally occurring, inorganic solids with a definite chemical composition and an ordered internal structure. These fascinating entities are defined by specific criteria: they are naturally occurring, solid, inorganic, and possess a unique crystal structure. These criteria help identify and classify most minerals.

Over 4,000 minerals have been identified in Earth’s crust, and the diversity is astounding. Many minerals and other minerals are found throughout the planet’s surface and interior.

Several key factors influence mineral classification: crystalline structure, inorganic nature, and natural formation. These aspects determine a mineral’s identity and properties. Minerals are categorized into mineral species based on their chemical compositions and structural characteristics.

Minerals are grouped into classes based on their anionic group, such as silicates, carbonates, and sulphates, which share similar properties and often form in related geologic environments. For example, mineral classes such as sulphates, nitrates, and carbonates are categorized by the type of anion present, with specific mineral species highlighted within each class.

Physical properties such as colour, hardness, and lustre are used by mineralogists to identify minerals, making the process accessible to anyone seeking to distinguish among different minerals.

What is a Mineral?

A mineral is a naturally occurring, inorganic, crystalline substance with a specific chemical composition and a defined atomic arrangement. These naturally occurring entities are the building blocks of rocks and are found in various environments, including the Earth’s crust, mantle, and core.

With over 4,000 known minerals, each has unique physical properties that help identify it. These properties include body colour (the inherent, visible hue of the mineral), which can be influenced by trace elements—small amounts of impurities that often cause variations in colour.

However, colour can be misleading for minerals such as quartz and calcite, as many minerals can occur in various colours due to impurities. The streak of a mineral is the colour of its powdered form, which can differ from the mineral's body colour; a streak is the colour left behind on an unglazed porcelain plate.

Other properties include crystal shape, hardness, cleavage, lustre (how light interacts with the mineral's surface), magnetism, ability to transmit light (such as whether the mineral is a transparent mineral or belongs to translucent minerals, determined by how much light passes through), and specific gravity.

The way light passes through a mineral and the appearance of its surface are used for identification, as they affect properties such as transparency, translucency, and reflectivity. Understanding these characteristics is essential for identifying minerals and appreciating their role in the Earth’s geological processes.

Inorganic Nature

Minerals are inherently inorganic, meaning they are not derived from living organisms. This distinction separates minerals from organic compounds. Inorganic substances lack the carbon-based structures typical of organic materials, making minerals unique in their composition and formation.

Natural Formation

Another defining characteristic is the natural formation of minerals. True minerals form through geological processes such as cooling, evaporation, and precipitation that occur naturally in Earth's crust. Natural formation distinguishes minerals from synthetic alternatives, ensuring their authenticity in geological studies.

Geological Processes

Geological processes are central to how minerals form, transform, and are ultimately classified. These natural processes—igneous, sedimentary, and metamorphic—shape the Earth’s crust and determine the chemical composition, crystal structure, and physical properties of the minerals we find and cherish today.

Igneous Processes

Igneous processes begin deep within the Earth, where intense heat melts rock into magma. As this magma cools and solidifies, it forms igneous rocks, giving rise to a variety of minerals. Silicate minerals, such as quartz and feldspar, are especially common in igneous rocks, thanks to their stable silicate tetrahedra structures. The specific conditions during cooling—like temperature and pressure—directly influence the crystal structure and size of the minerals that form.

Sedimentary Processes

Sedimentary processes take over at the Earth’s surface, where rocks are broken down by weathering and erosion. These fragments, or sediments, are transported and eventually deposited in layers, where they compact and cement together to form sedimentary rocks. Minerals like calcite and gypsum often crystallize from dissolved ions in water, while accessory minerals and native elements, such as native copper, can be found as trace components within these rocks. The chemical composition and physical properties of minerals in sedimentary rocks are shaped by the environment in which they form, including the presence of water and other elements.

Metamorphic Processes

Metamorphic processes occur when existing rocks are subjected to high temperatures and pressures, often deep within the Earth’s crust. This causes minerals to recrystallize or transform into new minerals with different crystal structures and physical properties. For example, the transformation of limestone into marble involves the recrystallization of calcite, while the formation of new silicate minerals is common in metamorphic environments. Sulphide minerals can also form or change during these intense geological events.

Throughout these processes, minerals are constantly being created, altered, and destroyed—a cycle known as the rock cycle. This ongoing transformation explains the incredible diversity of minerals found in the Earth’s crust. Identifying minerals and classifying them accurately requires an understanding of the geological processes that shaped them, as these processes leave distinct signatures in a mineral’s chemical composition, crystal structure, and other physical properties.

Whether you’re a geologist, a gemstone enthusiast, or a lover of handmade jewelry, appreciating the role of geological processes deepens your connection to the natural beauty and history of every mineral. From the formation of dazzling silicate minerals in igneous rocks to the discovery of rare native elements and accessory minerals in sedimentary layers, the story of minerals is truly the story of our ever-changing planet.

With an understanding of how minerals form, we can now explore how they are grouped and classified.

Mineral Groups

Mineral groups are categories of minerals that share similar chemical compositions and crystal structures. These groups are essential for classifying minerals and understanding their properties and characteristics.

Major classifications of minerals include silicates, carbonates, oxides, sulphides, sulphates, halides, phosphates, and native elements.

Silicate Minerals

Silicate Minerals: Silicate minerals belong to the silicate group, the most abundant group in the Earth's crust, making up over 90% of it. They contain silicon and oxygen atoms arranged in a tetrahedral structure. The silicate group includes framework silicates (e.g., quartz and feldspar) and ring silicates (cyclosilicates) such as tourmaline, beryl, and cordierite, which have ring-shaped silicate groups, such as [Si6O18]12−. Many gemstones are categorized as silicates, reflecting the structural and compositional diversity of this group. These minerals are crucial to the formation of igneous, sedimentary, and metamorphic rocks, making them significant in geology and mineralogy.

Carbonate Minerals

Carbonate Minerals: Carbonate minerals are based on the carbonate ion (CO3)2− combined with a metal atom. This group includes important gemstones such as calcite and aragonite, which react with acid. These minerals are often found in sedimentary rocks and are vital in geological processes. Common examples include calcite, dolomite, and limestone. Carbonate minerals form in environments where sedimentation occurs, such as marine settings.

Sulphate Minerals

Sulphate Minerals: Sulphate minerals contain sulphur and oxygen, represented by the sulphate ion SO4^2−, and are typically found in evaporite deposits. These minerals form from the evaporation of sulphide-rich waters. Examples include gypsum, anhydrite, and barite. Sulphate minerals are significant in studying sedimentary environments and the processes that lead to their formation.

Halide Minerals

Halide Minerals: Halide minerals are composed of a halogen element, such as chlorine or fluorine, combined with a metal atom. These minerals often form through the evaporation of saltwater. Examples include halite (rock salt), sylvite, and fluorite. Table salt is the mineral halite, a halide mineral. Halide minerals are known for their distinctive crystal structures and high solubility.

Phosphate Minerals

Phosphate Minerals: Phosphate minerals contain the phosphate ion, which includes phosphorus and oxygen. They are commonly found in igneous and metamorphic rocks and are scientifically and economically important, with applications in various industrial processes.

Oxide Minerals

Oxide Minerals: Oxides are minerals where oxygen is combined with one or more metals. Gemstones like ruby and sapphire are both varieties of the mineral corundum, which is classified as an oxide. Examples include hematite and magnetite, which are important sources of iron.

Sulphide Minerals

Sulphide Minerals: Sulphides are compounds that contain sulphur combined with a metal, like pyrite and galena. Sulphides tend to have high specific gravity, a soft and brittle structure, and are important ore minerals for economic extraction.

Native Elements

Native Elements: Native elements are minerals composed of a single element, such as native metals such as gold, silver, and copper. These native metals are naturally occurring metallic elements not chemically bonded to other elements, and are known for their high specific gravity and metallic bonding.

Minerals are also classified as metallic minerals or non-metallic minerals based on their lustre and composition. Nonmetallic lustre is an important property for identification, as nonmetallic minerals lack metallic lustre and include examples such as limestone, gypsum, and mica.

Understanding these mineral groups helps geologists and mineralogists classify and study minerals, providing insights into their formation and properties.

Now that we've explored the main mineral groups, let's look at the properties that help us identify and distinguish them.

Mineral Properties

Mineral properties are the defining characteristics that help identify and distinguish minerals from one another. These properties can be broadly categorized as physical, optical, and chemical, each crucial for identifying minerals.

Physical Properties

Crystal Habit: The typical external shape or appearance of mineral crystals.
Crystal Form: The characteristic geometric shape of a mineral, such as cubes, dodecahedral crystals, or needle-like crystals.
Hardness: Resistance to scratching, measured by the Mohs scale.
Lustre: How light interacts with the mineral's surface (metallic or non-metallic).
Colour: The visible hue of the mineral, which can be influenced by impurities.
Streak: The colour of the powdered mineral, often tested on an unglazed porcelain plate.
Cleavage: The tendency of a mineral to break along specific planes of weakness in its crystal structure.
Fracture: The way a mineral breaks when it does not cleave, such as a conchoidal fracture (smooth, curved surfaces).
Specific Gravity: The density of the mineral compared to water.
Magnetism: Some minerals are magnetic, which can aid identification.

Crystal habit and crystal form are influenced by environmental conditions during mineral formation and are key to mineral identification. Cleavage is the tendency of a mineral to break along specific planes of weakness in its crystal structure, while conchoidal fracture describes a type of breakage that creates smooth, curved surfaces, as seen in quartz.

Optical Properties

Transparency: How much light passes through a mineral (transparent, translucent, or opaque).
Reflectivity: How much light is reflected from the mineral's surface.
Fluorescence: Some minerals glow under UV light.

Chemical Properties

Reactivity: How a mineral reacts with acids or other chemicals.
Composition: The specific elements and their arrangement within the mineral.

Chemistry and crystal structure together determine mineral classification, physical properties, and polymorphic forms. The internal atomic structure of minerals can be determined through X-ray diffraction, which helps in understanding their classification and identification.

With a grasp of mineral properties, we can now examine how minerals are classified by their chemical composition.

Classification by Chemical Composition

Minerals are primarily classified by their chemical composition and internal crystal structure. This classification method categorizes minerals based on their elements, structural arrangement, and chemical formula. Chemical bonds within minerals influence properties such as cleavage and lustre, which are important for classification.

Major Mineral Groups by Chemical Composition

Based on their chemical composition, minerals are divided into eight main groups:

Silicates
Native Elements
Carbonates
Halides
Oxides
Hydroxides
Sulfates
Phosphates

Each group has distinct characteristics and properties; within these groups, specific mineral species are categorized based on their unique chemical compositions and crystal structures. Minerals in their pure form have well-defined chemical compositions and crystal structures, which are important for accurate classification.