Minerals are chemical compounds and simple substances with a crystalline structure and a clearly defined chemical composition formed as a result of geological and cosmic processes. Minerals are fundamental components of the Earth’s crust. The science that studies minerals, their origins, and species diversity is mineralogy.
Classification of Minerals
The first broad classification of known minerals was proposed by the American mineralogist James Dana. His work, “System of Mineralogy,” first published in 1837, marked a significant step in the classification and study of minerals. In this work, Dana introduced a systematic classification of minerals, which was later expanded and modified by other scientists.
Dana identified five main classes of minerals:
- Native Elements: This class includes pure chemical elements such as silver, graphite, and others.
- Sulfides and Arsenides: This class comprises minerals containing sulfides or arsenides, for example, pyrite (iron sulfide) and galena (lead sulfide).
- Halides: This category included minerals containing salts or halides, such as halite (sodium chloride).
- Oxides: This class consisted of minerals containing oxide groups, including rutile (titanium dioxide) and cassiterite (tin oxide).
- Organic Compounds: Dana also included minerals containing organic compounds in the classification. This could include guano, which contains organic remains of birds and other organisms.
This classification reflected the state of analytical chemistry in the mid-19th century.
The development of X-ray structural methods in the early 20th century, as pioneered by W. L. Bragg, revealed the wide variability of mineral structures and their pivotal role in shaping the physical and chemical properties of minerals. It became clear that the inclusion of a structural component in mineral classification was essential. Various variants of crystal-chemical mineral classification systems were proposed by G. Strunz (Mineralogische Tabellen, 1941), E. Lazarenko (1953), O. Povarennykh (1970), O. Godovikov (1983, 1999), J. Lima-de-Faria (2001).
The classification of mineral species based on chemical composition and structure plays a vital role in the study and categorization of minerals.
Criteria for the systematic classification of mineral species:
- Native Elements: Composed of pure chemical elements, such as diamond (carbon), silver, sulfur, and others.
- Sulfides and Their Analogues: Containing sulfides (e.g., pyrite) or similar compounds, including arsenides, selenides, tellurides, stibnites, and bismuthides.
- Sulfosalts: Minerals containing salts that encompass sulfide components.
- Oxides and Hydroxides: Comprising oxides (e.g., rutile) and hydroxides.
- Oxysalts: Minerals including various classes of compounds such as silicates, borates, phosphates, vanadates, arsenates, tungstates, molybdates, chromates, sulfates, and carbonates.
- Halides: Containing halogens (fluorine, chlorine, bromine, iodine) as part of their chemical structure.
- Coordination: Minerals with a complex structure with atoms or ions organized into coordination complexes. This category includes silicates.
- Isolated: Minerals that form as separate atoms or ions but do not combine into complex structures. Examples include graphite.
- Chain: Minerals in which atoms or groups of atoms are organized into chains. Examples are pyrite and actinolite.
- Sheet: Minerals with atoms or groups of atoms organized into sheets. Mica is a typical example.
- Framework: Minerals in which atoms are arranged in a three-dimensional crystal lattice with a large number of cavities. This group includes various silicates and haloselenides.
These criteria help systematize minerals and identify their main classes based on their chemical nature and structure. Such classification is crucial for the study and understanding of the diversity of the mineral world.
Key Characteristics of Minerals
The main characteristics of minerals include:
- Hardness: Minerals are solid substances, and their hardness can vary from very soft (e.g., gypsum) to very hard (e.g., diamond).
- Crystal Structure: Most minerals have a crystalline structure, meaning their atoms or ions are arranged in regular geometric patterns relative to one another.
- Chemical Composition: Each mineral has a specific chemical composition, consisting of certain chemical elements or compounds. For example, quartz is a mineral composed of silicon and oxygen atoms.
- Color: The color of a mineral can be one of its identifying features, though it can vary or be different from sample to sample.
- Luster: Luster refers to how a mineral interacts with light and can be metallic, non-metallic, vitreous, resinous, and other types.
- Diaphaneity: Diaphaneity refers to a mineral’s transparency or translucency. Minerals can be transparent, translucent, or opaque.
- Cleavage: Some minerals can be easily split along flat planes that define their crystalline structure. This is known as cleavage.
- Optical Properties: May exhibit various optical properties, such as double refraction (birefringence) or pleochroism.
- Specific Gravity: The specific gravity is the ratio of a mineral’s density to the density of water and is a measure of its relative heaviness.
- Magnetism: Can show various magnetic properties, such as diamagnetism, paramagnetism, or ferromagnetism.
Minerals are used in geology for studying geological formations and underground resources. They are also utilized