Minerals: Definition and Elements

Study Notes

Defined as a naturally occurring, inorganic, crystalline solid with a definitive chemical composition, minerals exhibit distinct physical and chemical properties that can be used for identification and classification. The strict definitions help geologists and mineralogists to categorize various substances in nature and understand their formation and occurrences.
Minerals are the fundamental building blocks of all rocks and can be composed of one or more types. This composition leads to a diversity of rock types, as minerals aggregate in different ways to form sedimentary, igneous, and metamorphic rocks. Understanding the composition and properties of minerals is essential for studying the Earth's processes and its geological history.

Elements are the basic building blocks of all minerals, with every mineral consisting of one or more elements. These elements dictate the mineral's chemical behavior and physical properties, including hardness, color, luster, and cleavage patterns. The periodic table serves as a reference for identifying these elements and comprehending their interactions in various mineral formations.
Examples of minerals and their chemical formulas include:
- Pyrite: [FeS2]
- Malachite: [Cu2CO3(OH)2]
- Ice: [H2O]

Minerals originate through geological processes in nature and are not made by living organisms, classifying them as inorganic. The processes involved in mineral formation include cooling and solidification of magma, crystallization from solutions, and changes occurring due to pressure and temperature. Recognizing the natural origin of minerals emphasizes their role in Earth's systems and the cycle of matter.
Diamonds serve as an example of a naturally occurring mineral composed of carbon (C). Their formation occurs deep within the Earth, usually at high pressures and temperatures, and they are brought to the surface through volcanic activity. The unique crystalline structure of diamonds contributes to their exceptional hardness, making them valuable both industrially and as gemstones.

Atoms in minerals are organized in an orderly, repeating three-dimensional structure, contributing to their solidity and distinct characteristics. This crystalline arrangement defines the symmetry and form of minerals, which can be observed in their crystal faces. The systematic arrangement of atoms not only influences a mineral’s physical properties but also affects how it interacts with light, which is critical for identifying minerals.

A mineral’s chemical composition can be fixed or variable within certain limits. Fixed composition minerals maintain a constant ratio of elements, asserting a rigidity in their chemical identity. Conversely, others like feldspar can have a range of compositions depending on variations of elements (e.g., potassium vs. sodium feldspar), which can lead to significant differences in properties such as color, density, and melting point.
Some minerals, like halite ([NaCl]) or quartz ([SiO2]), have fixed compositions, while others like feldspar can have a range of compositions depending on variations of elements. Understanding the specific chemical make-up of a mineral allows for better predictions of its behavior in geological processes as well as its potential uses in industry or technology.

Impurities, or trace elements, can modify the appearance and value of minerals. The presence of even small amounts of different elements can lead to noticeable differences in color, hardness, and other physical properties. Thus, impurities can be significant in determining both the aesthetic appeal and the economic value of various minerals.
Varieties of corundum, such as ruby and sapphire, differ in color and worth due to specific impurities present. For example, rubies derive their rich red color from chromium impurities, while sapphires can appear in a range of colors based on the various trace elements included in their composition. These distinctions highlight the importance of understanding mineral impurities for gemology and mineral exploration.