Compare the chemical formula of magnetite with that of biotite. Why do we mine magnetite to obtain iron supplies, but we don't mine biotite? (C)

Understanding the chemical makeup of minerals is crucial for determining their uses. In the case of magnetite (Fe₃O₄) and biotite (K(Mg,Fe)₃(AlSi₃)O₁₀(OH,F)₂), we observe distinct differences in their formulas. Magnetite contains three iron (Fe) atoms as an integral part of its chemical structure. The chemical formula indicates that each molecule of magnetite will consistently contain iron, showcasing predictability in its composition.

On the other hand, biotite's formula reveals a more complex composition, with iron being just one of several possible elements. The presence of potassium (K), magnesium (Mg), aluminum (Al), silicon (Si), oxygen (O), hydrogen (OH), and fluorine (F) alongside iron suggests variability. Notably, in biotite, the iron can be replaced by magnesium, indicating that iron is not always present in a fixed amount as it is in magnetite. This comparison emphasizes the higher and more stable content of iron in magnetite, which is a significant factor when considering mineral extraction for iron supplies.

Iron extraction is a fundamental industrial process, which involves separating the desired metal from its ore. Magnetite, with its straightforward chemical formula of Fe₃O₄, comprising a substantial amount of iron, is an ideal candidate for this process. The mineral's high iron content simplifies the smelting process, allowing for the efficient production of iron.

The steps involved in extracting iron from magnetite include crushing the ore, concentrating the iron using magnetic separation, and then reducing the iron oxide at high temperatures in a blast furnace. This reduction reaction generally involves carbon in the form of coke, which reacts with the iron oxide to produce pure iron and carbon dioxide. Due to the predictable and rich presence of iron in magnetite, these steps are more straightforward and cost-effective, highlighting why this mineral is preferred in iron extraction.

When distinguishing between magnetite and biotite for the purpose of iron extraction, several factors stand out. Magnetite is primarily an iron oxide mineral and is magnetic, making it easily separated from other materials using magnetic separation techniques. This property, paired with its dense concentration of iron, renders it an exemplary source for iron production.

Biotite, however, is a sheet silicate or mica, with varying elemental compositions that can include iron but not consistently. The layered structure of mica makes the extraction of iron more complex and less direct. Moreover, the potential replacement of iron with magnesium makes biotite an unreliable source for iron extraction. The mining and refining processes that would be required to extract iron from biotite are less straightforward and more expensive, further corroborating why magnetite takes precedence over biotite in the iron industry.

The composition of a mineral dictates its properties and, consequently, its applications. Mineral composition is identified through the mineral's chemical formula and crystalline structure. In our comparison of magnetite and biotite, we see how composition impacts the viability of a mineral for iron extraction. Magnetite's uniform composition, dominated by iron atoms aligned in a lattice structure, not only facilitates iron extraction but also conveys magnetic properties that are advantageous in the separation process.

Biotite's diverse elements and flexible substitution between them lead to varying properties, which is less desirable for specific industrial applications such as iron production. Therefore, a mineral's composition is a key determinant in the mining and extraction processes, influencing the economic benefits and feasibility of its use in various industries.