The term “mineral” has a dual definition, depending on whether it is viewed through a geological or a nutritional lens. Geologically, a mineral is a naturally occurring, homogeneous solid with a specific chemical composition and an ordered crystalline structure. These substances form through inorganic processes within the Earth and make up the planet’s rocks and sands.
In human nutrition, a mineral refers to any inorganic chemical element required by the body for proper physiological function. Nutritional minerals, such as iron, calcium, and zinc, are essential components of a healthy diet. This article explores the locations of these substances, from their geological origins to their presence in the biosphere and the food we consume.
Earth’s Fundamental Geological Reservoirs
The majority of the Earth’s mineral content is held within its deep internal structure, primarily the crust, mantle, and hydrosphere. The Earth’s Crust, the outermost layer, is the most accessible reservoir and is dominated by silicate minerals. Elements like oxygen and silicon make up over 74% of the crust’s mass, forming minerals such as quartz and feldspar.
The Earth’s Mantle, which extends hundreds of kilometers below the crust, is the largest layer by volume and is rich in ferromagnesian silicate minerals. The signature rock is peridotite, which is dense and composed mainly of minerals like olivine and pyroxene, containing high amounts of iron and magnesium. These minerals serve as the source material for many crustal minerals.
Beyond the solid earth, the Hydrosphere—the Earth’s water bodies—holds minerals in a dissolved state. Ocean water is a massive reservoir of dissolved salts, including sodium and chlorine, which are the components of halite (common table salt). The hydrosphere also contains trace elements which, though present in low concentrations, represent significant total amounts due to the sheer volume of the oceans.
Processes That Create Mineral Concentrations
While minerals are globally distributed, specific geological processes concentrate them into distinct, often economically valuable deposits. Igneous Processes involve the crystallization of minerals directly from molten rock (magma). As magma cools, minerals crystallize in a specific sequence. Late-stage magmatic fluids can enrich certain elements, forming veins or large deposits of minerals like chromite or magnetite.
Sedimentary Processes involve the deposition and precipitation of minerals from water bodies or the accumulation of weathered rock fragments. Evaporite deposits form when large bodies of water dry up, causing dissolved minerals like gypsum, halite, and potash to precipitate and accumulate in layers. Banded iron formations, formed by the chemical precipitation of iron oxides in ancient oceans, are another example of sedimentary deposits.
Metamorphic and Hydrothermal Processes often work together to create high-grade mineral deposits. Hydrothermal processes involve the circulation of hot, mineral-rich water through fractures in the Earth’s crust. This water dissolves elements from surrounding rocks and precipitates them in concentrated form as the fluid cools or its chemistry changes, creating ore veins rich in metals like gold, copper, and lead. Metamorphism, driven by intense heat and pressure, causes minerals within a rock to recrystallize into new, stable forms, sometimes releasing fluids that feed these hydrothermal systems.
Minerals in the Biosphere and Human Nutrition
The journey of geological minerals into the human diet begins with the Soil Matrix, which acts as the intermediary between the Earth’s crust and the biosphere. Weathering (the physical and chemical breakdown of rocks) releases mineral elements into the soil, making them available to living organisms. The availability of these elements is influenced by factors like soil texture, pH, and the presence of organic matter.
Plant Uptake is a selective mechanism by which plants absorb mineral ions from the soil water through their roots. Plants convert these inorganic elements into organic, bioavailable forms that enter the food chain. The mineral content of a crop is directly related to the concentration of plant-available nutrients in the soil.
For humans, the ultimate destination is Dietary Sources, where essential minerals are found in various foods and water. Calcium is found in dairy products, fortified foods, and leafy green vegetables like kale and broccoli. Iron is abundant in red meat, poultry, fish, and legumes. Iodine is primarily obtained from iodized salt and seafood, while trace elements like zinc and selenium are found in whole grains, nuts, and meats.