Key Economic Minerals

Why This Matters

Economic minerals form the foundation of modern civilization—from the copper wiring in your walls to the silicon chips in your phone. In mineralogy, you're not just memorizing mineral names; you're being tested on crystal chemistry, formation environments, and physical properties that determine why certain minerals become economically valuable. Understanding the relationship between a mineral's atomic structure and its industrial applications is central to exam success.

These minerals also illustrate key concepts like ore deposit formation, extraction geology, and mineral associations. When you encounter a question about why graphite conducts electricity while diamond doesn't (despite both being pure carbon), you need to connect crystal structure to properties. Don't just memorize what each mineral is used for—know why its chemistry and formation make it suitable for that use.

---

Native Elements and Precious Metals

These minerals occur in their elemental form or as high-value metals, prized for unique physical and chemical properties that make them resistant to corrosion and excellent conductors.

Gold

• Native element with exceptional malleability and corrosion resistance—its face-centered cubic structure allows atoms to slide past each other without breaking bonds
• Hydrothermal origin in most economic deposits, precipitating from hot fluids in quartz veins and concentrated in placer deposits through weathering
• High density (19.3 g/cm³) makes gravity separation effective for extraction and explains concentration in alluvial deposits

Silver

• Highest electrical and thermal conductivity of any element—critical for electronics, solar panels, and photography
• Occurs as native silver and in sulfide ores like argentite ($Ag_2S$) and as a byproduct of galena ($PbS$) processing
• Tarnishes readily due to reaction with atmospheric sulfur, forming silver sulfide—a key identification feature

Copper

• Second-highest electrical conductivity after silver—the standard for electrical wiring due to lower cost and excellent ductility
• Primary ores are sulfides including chalcopyrite ($CuFeS_2$) and bornite ($Cu_5FeS_4$), formed in porphyry copper deposits
• Highly recyclable with no loss of properties, making it economically and environmentally significant

---

Industrial Metals and Their Ores

These minerals serve as the raw materials for steel, aluminum, and other structural metals that form the backbone of construction and manufacturing.

Iron Ore (Hematite and Magnetite)

• Hematite ($Fe_2O_3$) contains ~70% iron—the primary ore for steel production, identified by its red streak and metallic to earthy luster
• Magnetite ($Fe_3O_4$) is strongly magnetic—forms in igneous and metamorphic environments and serves as a key indicator mineral in exploration
• Banded iron formations (BIFs) represent ancient sedimentary deposits formed when Earth's atmosphere first became oxygenated

Bauxite (Aluminum Ore)

• Mixture of aluminum hydroxides including gibbsite, boehmite, and diaspore—not a single mineral but an ore rock
• Forms through intense tropical weathering (laterization)—silica and other elements leach away, concentrating aluminum oxides
• Requires enormous energy for smelting via the Hall-Héroult process, making aluminum recycling economically critical

---

Carbon Polymorphs

These minerals demonstrate how identical chemistry produces radically different properties based on crystal structure—a fundamental mineralogy concept.

Diamond

• Hardest natural material (10 on Mohs scale)—each carbon atom covalently bonded to four neighbors in a tetrahedral network
• Forms at extreme conditions (>150 km depth, >5 GPa pressure) and reaches the surface rapidly via kimberlite pipe eruptions
• Industrial applications dominate production—cutting, drilling, and abrasive tools consume far more diamond than the gem market

Graphite

• Excellent electrical conductor despite being pure carbon—layered hexagonal sheets with delocalized electrons between layers
• Extreme softness (1-2 on Mohs scale) due to weak van der Waals forces between carbon sheets, making it an ideal lubricant
• Forms in metamorphic environments from organic carbon in sediments or through reduction of carbonates

---

Silicate Industrial Minerals

The silicate minerals dominate Earth's crust and provide essential raw materials for ceramics, glass, and electronics industries.

Quartz (Silica)

• Composed of $SiO_2$ in a continuous tetrahedral framework—piezoelectric properties make it essential for electronics and timekeeping
• Extremely abundant and chemically stable—primary source of silicon for semiconductors and glass manufacturing
• Occurs in all rock types with varieties including amethyst, citrine, and chalcedony based on trace elements and crystal habit

Feldspar

• Most abundant mineral group in Earth's crust (~60%)—aluminum silicates with potassium, sodium, or calcium
• Two main series: alkali feldspars and plagioclase—composition determines melting behavior critical for ceramic glazes
• Weathers to clay minerals—the primary source of kaolin used in ceramics, paper, and pharmaceuticals

Mica

• Perfect basal cleavage allows splitting into flexible, transparent sheets—result of layered silicate structure with weak interlayer bonds
• Muscovite ($KAl_2(AlSi_3O_{10})(OH)_2$) is an excellent electrical insulator—used in capacitors and high-temperature applications
• Common in pegmatites and metamorphic rocks—large crystals form during slow cooling of silica-rich melts

---

Evaporite Minerals

These minerals form through evaporation of water bodies, concentrating dissolved ions into economic deposits. Their high solubility distinguishes them from most other mineral groups.

Halite (Rock Salt)

• Composed of $NaCl$ in cubic crystal system—perfect cubic cleavage and salty taste are diagnostic properties
• Forms in evaporite sequences as seawater or lake water evaporates, often interbedded with gypsum and anhydrite
• Critical for chemical industry as feedstock for chlorine, sodium hydroxide, and countless industrial processes

Gypsum

• Calcium sulfate dihydrate ($CaSO_4 \cdot 2H_2O$)—loses water when heated to form plaster of Paris
• Very soft (2 on Mohs scale) with perfect cleavage in one direction—easily scratched with fingernail
• Precipitates before halite in evaporating seawater due to lower solubility, creating predictable stratigraphic sequences

---

Soft Industrial Minerals

These minerals are valued precisely for their low hardness and unique physical properties, demonstrating that economic value doesn't always correlate with durability.

Talc

• Softest mineral (1 on Mohs scale)—layered magnesium silicate ($Mg_3Si_4O_{10}(OH)_2$) with extremely weak interlayer bonds
• Greasy feel and chemical inertness make it ideal for cosmetics, pharmaceuticals, and as an industrial filler
• Forms through metamorphism of ultramafic rocks—often associated with serpentine and chlorite in metamorphic terranes

Sulfur

• Native element forming orthorhombic crystals—bright yellow color and low melting point (115°C) are diagnostic
• Essential for sulfuric acid production—the most-produced industrial chemical, used in fertilizers, batteries, and refining
• Volcanic and biogenic origins—forms around fumaroles and through bacterial reduction of sulfate in sediments

Calcite (Limestone)

• Calcium carbonate ($CaCO_3$) with perfect rhombohedral cleavage—reacts vigorously with dilute HCl (fizz test)
• Biogenic and chemical precipitation in marine environments—shells, coral, and direct precipitation from seawater
• Foundation of cement and construction industry—also critical for agriculture as soil amendment and in steel flux

---

Quick Reference Table

---

Self-Check Questions

1. Diamond and graphite are both pure carbon—what structural difference explains why diamond is the hardest mineral while graphite is one of the softest?

2. Which two evaporite minerals would you expect to find together in an ancient marine sequence, and which precipitates first based on solubility?

3. Compare and contrast the formation environments of bauxite and iron ore (BIF)—what weathering or depositional processes concentrate each metal?

4. If an FRQ asks you to explain why copper and silver are both used in electronics, what property do they share, and what economic factor makes copper more common in household wiring?

5. Identify two sheet silicate minerals from this list and explain how their layered structure determines their industrial applications.