Minerals are naturally-occurring solids with specific chemical composition and ordered internal atomic arrangements that differ significantly from synthetic (laboratory-produced) chemicals.
Some minerals are transparent and allow light to pass through while others are opaque; yet still others exhibit special optical qualities, including fluorescence for glowing-in-the-dark effects.
Crystallization
Crystals form when the atoms in a mineral join together in an orderly repeating pattern to create a highly ordered repeating structure called a crystal. They may form naturally, such as snowflakes falling, or artificially produced in labs to produce pure minerals.
Process complexity makes the procedure challenging; for instance, it may take some time before solute concentration reaches crystallization threshold and thus becomes supersaturated in solution form.
Scientists utilize solubility curves to model this complex process and predict which factors influence it. Achieving crystallization in a laboratory often relies on experimentation, observation, imagination and skill rather than mathematical and physical predictions alone.
Weathering
Low pressures and temperatures at Earth’s surface render many minerals less stable than they were when formed, forcing them to change into new minerals by chemical weathering (chemical change to adapt to their new environments at surface).
Chemical weathering is driven by weak acids produced in the water cycle, such as carbonic acid. These acids dissolve certain minerals such as silicates.
Physical erosion increases chemical weathering rates by exposing fresh mineral surfaces to acidic solutions, and Millot et al.’s research of granitoid watersheds demonstrated this correlation closely.
Plants increase chemical weathering by producing organic acids and contributing to physical weathering by widening rock cracks. Mycorrhizal fungi associated with tree roots also have a beneficial impact on mineral stability by providing inorganic nutrients.
Twinning
Over geological time, minerals transform into different mineral forms known as “twinning.” Twins may form through growth, transformation or deformation processes.
Growth twins occur when atoms in different crystal domains are displaced in an identical fashion but with differing orientation, creating twinned minerals with similar composition but unique crystal structures. Growth twins can serve as an invaluable diagnostic tool when it comes to mineral identification.
Complex twinning occurs in some minerals when atoms in different twin domains are related in various ways, as demonstrated by plagioclase with its distinctive striations patterns (Figure 4.43). Hand specimens may make complex twins hard to detect; one diagnostic feature for complex twins would be reentrant angles such as those seen in Figure 4.45’s twinned cyrussite crystal.
Striations
Glaciers move over rocks at tremendous speed, leaving a trail of marks known as striations to indicate which way glaciers have moved over time. Scientists use them as indicators of where glaciers have traveled over time.
Mineral demand will expand significantly with the growing use of clean energy technologies, with electric vehicle (EV) batteries needing lithium, nickel, graphite, cobalt and rare earth elements as well as electricity networks needing significant quantities of copper.
Responsible management of minerals can be challenging, with potentially adverse environmental and social ramifications including greenhouse gas emissions, land use change, water depletion and pollution, corruption, human rights abuses and corruption arising as potential results. Supply chain due diligence combined with monitoring and enforcement will be essential. Achieve these objectives will require strong global policy signals as well as cooperation among governments, companies, communities and stockpiling facilities – this may also play an integral part in mitigating risks.
Cleavage
Cleavage refers to the tendency for minerals to fracture along planes and produce mineral fragments with distinct shapes; it serves as an effective diagnostic property and its quality and direction depend upon how atoms arrange themselves within its crystal lattice.
Some minerals, like galena, exhibit complete cleavage in three directions while others like mica exhibit good cleavage in two. If modified crystals exhibit this trait, the number of directions should also be written on their sample with “All Sides.”
Cleavage differs from parting, which occurs as irregular planes of weakness in minerals that do not possess natural cleavage (such as calcite). Please refer to your mineral sample guide for assistance on differentiating between these two features.
