Minerals are nonliving materials with distinct chemical composition and form beautiful crystals that reflect light in different ways. Minerals form in nature through three main processes: (1) precipitation from aqueous solutions through temperature variation; (2) crystallization from magma by heat change and (3) biological precipitation by living organisms.
Gypsum was one of the earliest silicate minerals, made up of calcium and phosphorus. Another widely occurring form is clay mineral kaolinite which features silicon-oxygen tetrahedra connected by aluminum octahedra in tetrahedral sheets.
Calcite
Calcite is the most prevalent natural calcium carbonate (CaCO3) mineral found in almost any environment. When pure, calcite is colorless but depending on impurities can appear reddish pink yellow greenish blueish brown or even black in appearance. Furthermore, it exhibits perfect rhombohedral cleavage and exhibits double refraction properties.
Calcite forms in sedimentary environments when marine organisms harvest calcium and carbonate ions from seawater to construct shells and skeletons for themselves. Over time, these minerals cement together into limestone and marble deposits. Calcite is also the main constituent of travertine deposits formed in hot springs.
NHMU’s collection features several exquisite calcite specimens, such as crystal twins, honey-colored scalenohedrons and doubly terminated calcites filled with sand inclusions – these can all be seen on our third floor Earth Lab and many others such as those used to form cave stalactites and stalagmites are also made from this mineral.
Pyrite
Pyrite gets its name from the Greek word for fire as it produces sparks when struck against metal surfaces. This property was highly prized during human survival’s early days when making fire was essential to survival.
Pyrite is an important source of sulfur, used to produce sulfuric acid – one of the world’s most manufactured chemicals, produced annually in greater amounts than any other.
Pyrite can also be used in industrial processes to make iron sulfate, used in fertilizers and other chemical processes, cleaning products, and also to extract iron from water sources. This application of pyrite makes pyrite valuable as an industrial material.
Pyrite can form through various processes, such as SRB in organic muds or coal shale or hydrothermal environments, or hydrothermally. Most commonly seen in nature as globular aggregates of euhedral crystals known as framboids with diameters less than 0.1 millimeter. They usually display brassy yellow to brassy orange hues but can also appear silver, bronze, or even black depending on where they form.
Pyroxenes
Pyroxene minerals play an essential role in understanding both igneous and metamorphic rocks, providing insight into volcanic and tectonic processes as well as geological temperatures over time. Pyroxenes act as geothermometers and barometers to reveal geological temperatures over time as well as provide information about magma composition and sources. Advanced analytical tools are used to map their atomic arrangements as well as map their cleavage planes – this makes pyroxenes invaluable tools for ceramic and refractory applications!
Pyroxene minerals include clinopyroxenes such as diopside, hedenbergite, and augite and orthopyroxenes like enstatite, johannsenite, omphacite and spodumene; these forms have lower silica contents than their feldspar counterparts.
Orthopyroxenes feature a hexagonal crystal structure and contain calcium, magnesium and iron atoms in coordination. Clinopyroxenes feature an M1 site comprised of six oxygen atoms in coordination while orthopyroxenes’ M1 and M2 sites form a larger irregular polyhedron with eight oxygen atoms arranged into four hexagonal rows in coordination with each other.
Sulfides
Sulfide minerals are among the most essential metal- and semimetal ores. Their structures consist of close-packing combinations of sulfur with metals or semimetals (usually six basic types), depending on ionic size and charge; color can often provide a good way to identify them – examples include pyrite (FeS), realgar (AsS), orpiment (As2S3) are good examples; van der Waals interactions crosslink sulfur atoms to form molecular chains with van der Waals interactions crosslinking sulfur atoms across molecular chains while stabilisation depends on ionic substitutional and bridging bonds within their structures; this makes sulfides ideal ores which is why pyrite (FeS), realgar (AsS), orpiment (As2S3) forms stable structures which allows their identification easily – such as when colored pigmented from their identification.
Sulfide minerals play an integral role in biological and ecological processes, supporting chemosynthetic microbes at hydrothermal vents in the deep ocean, creating habitats, nutrient cycling and providing energy to microbes – essential elements in maintaining ecological equilibrium. Mining for copper, gold or other metals from these ore deposits requires understanding their geology occurrence, chemical properties, phase relations and formation by mineralogists and geochemists who study mineralogical and geochemical aspects as well as potential environmental repercussions. Mineralogists and geochemists study these mineral extraction operations while mining for ore can produce copper ore; mining for other metals is of growing concern due to environmental implications related to mining operations sulfides from mined ore deposits containing metals.
