Naturally occurring, inorganic solids with definite compositions and ordered crystal structures — the building blocks of rocks, technology, and civilization
You have probably held a mineral without thinking much about it. Table salt is a mineral. So is the graphite in a pencil, the quartz in a sidewalk, and the copper wire inside a phone charger. The gemstones in jewelry, the iron in a skillet, the calcium in a tooth — all of these trace back to minerals formed inside Earth or at its surface over millions of years.
Minerals are the building blocks of rocks, and rocks are the building blocks of Earth's solid surface. Before we can understand how mountains form, how volcanoes erupt, how rocks change over time, or how natural resources are extracted, we need to understand minerals: what they are, how they form, and how we tell them apart.
This chapter introduces minerals as naturally occurring substances with specific compositions and internal structures. You will learn how to identify minerals by their physical properties, which minerals are most common in Earth's crust, which minerals are economically important, and how mining and mineral use create environmental challenges that Earth scientists help to study and address.
A jeweler calls a stone a diamond. A geologist wants to verify the claim. Without destroying the stone, what tests could identify it? By the end of this chapter, you will know a systematic approach — using crystal structure, hardness, luster, cleavage, streak, and density — that distinguishes diamond from every other clear mineral. The same approach identifies the rock-forming minerals that make up almost every rock on Earth.
Walk along a rocky beach and you will collect dozens of different materials — pebbles of different colors, textures, and weights. Look closely at a single pebble under a magnifying glass and you may see smaller, interlocking grains of different substances. Those individual substances are minerals.
A mineral is a naturally occurring, inorganic solid with a definite chemical composition and an ordered internal structure. Each part of that definition matters.
| Part of the Definition | What It Means | Why It Matters |
|---|---|---|
| Naturally occurring | Forms through natural geological processes, not in factories | Synthetic diamonds are not minerals; salt from a mine is |
| Inorganic | Not made by living organisms | Excludes coal, amber, pearl, bone |
| Solid | Fixed shape and volume at surface conditions | Liquid water is not a mineral; ice is |
| Definite chemical composition | Specific chemical formula or predictable range | Quartz is always SiO₂; halite is always NaCl |
| Ordered internal structure | Atoms in a regular, repeating 3-D pattern (crystal lattice) | Controls physical properties: shape, cleavage, hardness |
A rock is a naturally occurring solid made of one or more minerals. Granite is a rock made of quartz, feldspar, and mica. A single mineral is not a rock, though rocks made of only one mineral type do exist (marble is mostly calcite; quartzite is mostly quartz).
Glass looks like a mineral but is not one because it lacks an ordered internal structure. Atoms in glass are arranged randomly. Volcanic glass (obsidian) forms when lava cools so rapidly that atoms cannot arrange into a crystal lattice.
Organic materials — coal, wood, bone, shell — are not minerals because they contain carbon compounds produced by living organisms or come from biological processes.
Earth scientists have identified more than 5,000 minerals. However, only about a dozen mineral families — especially the silicates — make up the vast majority of all rocks. A few hundred additional minerals are economically important. The rest are rare, found only in specific geologic environments.
| Group | Key Chemistry | Common Examples |
|---|---|---|
| Silicates | Silicon + oxygen tetrahedra; ~90% of Earth's crust | Quartz, feldspar, mica, olivine, pyroxene, amphibole |
| Oxides | Oxygen bonded to a metal | Magnetite (Fe₃O₄), hematite (Fe₂O₃), corundum (Al₂O₃) |
| Carbonates | CO₃²⁻ bonded to a metal | Calcite (CaCO₃), dolomite (CaMg(CO₃)₂) |
| Sulfides | Sulfur bonded to a metal | Pyrite (FeS₂), galena (PbS), chalcopyrite (CuFeS₂) |
| Sulfates | SO₄²⁻ bonded to a metal | Gypsum (CaSO₄·2H₂O) |
| Halides | Halogen elements (Cl, F) | Halite (NaCl), fluorite (CaF₂) |
| Native elements | Single element in pure form | Gold (Au), silver (Ag), copper (Cu), diamond and graphite (C) |
All minerals have an ordered internal arrangement of atoms — a crystal structure. When minerals grow slowly in open space, they form crystals — geometric solids with flat faces, straight edges, and defined angles that reflect the internal atomic arrangement. Even irregular or dull-looking mineral samples have this internal order.
A mineral's crystal structure determines its physical properties — how it breaks, how it reflects light, how hard it is, and what shape it grows into. Two minerals can have identical chemical compositions but completely different structures and therefore very different properties.
Diamond vs. Graphite: Both are pure carbon. Diamond's atoms form a tight three-dimensional network → the hardest natural substance (Mohs 10). Graphite's atoms form flat sheets that slide past each other easily → soft enough to leave marks on paper (Mohs 1–2).
Four diagrams showing (1) the silicate tetrahedron: central Si atom surrounded by four O atoms in a pyramid; (2) isolated tetrahedra (olivine structure); (3) single chain of linked tetrahedra (pyroxene); (4) double chain (amphibole); (5) continuous sheet (mica). Labels connect structure to physical properties — sheet structure explains why mica peels into flat flakes.
| Formation Environment | Process | Mineral Examples |
|---|---|---|
| Cooling magma | Atoms organize as molten rock cools; rate of cooling controls crystal size | Olivine, pyroxene, feldspar, quartz, mica |
| Evaporating water | Dissolved substances precipitate as water evaporates from lake or sea | Halite, gypsum (evaporite deposits) |
| Hot water through rock cracks | Dissolved metals precipitate as hot water cools in fractures | Quartz veins, gold, galena |
| Metamorphic recrystallization | Heat and pressure reorganize existing minerals without full melting | Calcite in marble, garnet, staurolite |
| Surface and biological processes | Weathering reactions and biological extraction from water | Calcite in shells, clay minerals, iron oxides |
A mineral's identity reflects the conditions under which it formed. Geologists work in reverse: by identifying minerals in a rock, they reconstruct the temperatures, pressures, and chemical environments of that rock's origin. This is how Earth's history is read from rock.
Color is the most obvious property but often the least reliable for identification. Many minerals occur in several colors depending on trace impurities. Quartz is normally clear or white but can be purple (amethyst), yellow (citrine), pink (rose quartz), or gray (smoky quartz). Some minerals do have a consistent, diagnostic color — malachite is always green; sulfur is always yellow — but for most minerals, color alone should not be the deciding factor.
Streak is the color of a mineral's powder, produced by rubbing the mineral across an unglazed porcelain tile called a streak plate. The powder's color is more consistent than the mineral's surface color because impurities that affect surface appearance do not always affect the bulk powder.
Pyrite (fool's gold) has a shiny golden surface. Its streak, however, is greenish-black — nothing like real gold, which leaves a yellow streak. The streak test instantly resolves the confusion. Very hard minerals like quartz may scratch the streak plate instead of leaving a streak, making the test less useful for hard minerals.
Luster describes how a mineral's surface reflects light — not its color, but the quality of reflection.
| Luster Type | Description | Mineral Examples |
|---|---|---|
| Metallic | Reflects like a polished metal surface | Pyrite, galena, native copper, magnetite |
| Glassy (vitreous) | Reflects like broken glass | Quartz, halite, olivine |
| Pearly | Soft, iridescent, like a pearl | Muscovite mica, talc |
| Silky | Thread-like sheen from parallel fibrous structure | Fibrous gypsum (satin spar), asbestos |
| Resinous | Like amber or resin | Sphalerite |
| Earthy (dull) | No reflection; matte surface | Kaolin clay, limonite |
| Adamantine | Brilliant, intense reflection | Diamond |
Hardness is a mineral's resistance to being scratched. It is controlled by the strength of chemical bonds in the crystal structure. The Mohs Hardness Scale runs from 1 (softest) to 10 (hardest) using ten reference minerals.
| Mohs Number | Reference Mineral | Field Test |
|---|---|---|
| 1 | Talc | Scratched easily by a fingernail |
| 2 | Gypsum | Scratched by a fingernail |
| 3 | Calcite | Scratched by a copper coin |
| 4 | Fluorite | Scratched by a steel nail |
| 5 | Apatite | Scratched by a steel nail with difficulty |
| 6 | Orthoclase feldspar | Scratches glass |
| 7 | Quartz | Scratches glass easily |
| 8 | Topaz | Scratches quartz |
| 9 | Corundum | Scratches topaz |
| 10 | Diamond | Scratches everything |
A vertical bar showing 1–10 with reference minerals labeled. Everyday objects marked at approximate hardness: fingernail (~2.5) between gypsum and calcite; copper coin (~3) near calcite; steel knife blade (~5.5) between apatite and feldspar; glass plate (~5.5) at the same level. A caption emphasizes this is a relative, not absolute, scale — it tells which mineral scratches which, not by how much.
Hardness tests involve scratching, not breaking. A mineral that chips when you try to scratch it may appear softer than it really is. Always look for a true scratch mark, not a white powder residue left by the tool. If the unknown mineral leaves powder on the glass but the glass is unmarked, the glass is the harder material.
Cleavage is a mineral's tendency to break along flat, smooth, parallel planes — where chemical bonds are weakest in the crystal structure. Cleavage surfaces are flat, shiny, and reflect light in sheets. Cleavage is described by (1) the number of directions and (2) the quality (perfect, good, or poor).
| Cleavage Pattern | Description | Mineral Example |
|---|---|---|
| 1 direction, perfect | Peels into flat sheets | Mica |
| 2 directions, 90° | Breaks into rectangular blocks | Feldspar |
| 3 directions, 90° | Breaks into perfect cubes | Halite, galena |
| 3 directions, not 90° | Breaks into rhombohedra | Calcite |
| 4 directions | Breaks into octahedral fragments | Fluorite |
When a mineral breaks in directions that are not along cleavage planes, the break is called a fracture. Fracture surfaces are irregular or curved.
Conchoidal fracture produces curved, shell-like surfaces with smooth ripples — like the inside of a clamshell. Quartz and obsidian both break conchoidally. Quartz has no cleavage at all; it always fractures this way.
Two side-by-side illustrations. Left: mica splitting into flat, parallel sheets labeled "perfect one-directional cleavage" with arrows showing flat reflective planes. Right: a quartz crystal broken with curved conchoidal surfaces labeled "conchoidal fracture." Caption: cleavage produces flat, mirror-like surfaces that flash uniformly when the specimen is rotated under light; fracture surfaces are irregular and reflect light unevenly.
Crystal faces form as a crystal grows outward. Cleavage surfaces form when a crystal breaks. A natural crystal face that coincides with a cleavage direction will look similar to a cleavage surface, but the two form differently and for different reasons. Recognizing this distinction comes with practice — rotate the specimen and look for fresh, flat surfaces that reflect uniformly as a group.
Density is mass per unit volume, expressed in grams per cubic centimeter (g/cm³). Most silicate minerals have densities between 2.6 and 3.3 g/cm³. Minerals containing heavy metals are much denser: galena (PbS) has a density of about 7.6 g/cm³; gold is 19.3 g/cm³.
In the field, geologists estimate density by heft — the subjective sense of heaviness relative to size. A mineral that feels unusually heavy for its size probably contains heavy elements. In the lab, density is measured precisely by water displacement.
| Special Property | What It Is | Mineral(s) Identified |
|---|---|---|
| Magnetism | Attracts a compass needle or iron filings | Magnetite |
| Acid reaction | Fizzes (CO₂ bubbles) when touched with dilute HCl | Calcite (strongly); dolomite (when powdered) |
| Double refraction | Objects seen through clear crystal appear doubled | Calcite (Iceland spar) |
| Fluorescence | Glows under ultraviolet light | Fluorite (often blue-green), calcite, willemite |
| Taste | Salty taste (caution: do not taste unknown minerals) | Halite |
| Radioactivity | Detectable by Geiger counter | Uraninite, carnotite |
A small group of minerals makes up the overwhelming majority of rocks in Earth's crust. These rock-forming minerals must be identifiable quickly and confidently by any Earth scientist.
The feldspar group makes up roughly 60% of all crustal rocks. All feldspars contain silicon, aluminum, and oxygen; they differ in whether they also contain potassium, sodium, or calcium. Both types have a hardness of 6 and two cleavage directions at right angles.
Orthoclase (potassium feldspar) is typically pink or salmon-colored. Common in granite.
Plagioclase (sodium-calcium feldspar) is usually white or gray, and often shows fine parallel striations (lines) on cleavage surfaces caused by crystal twinning. Common in both granite and basalt.
Quartz (SiO₂) is extremely hard (Mohs 7), has no cleavage (only conchoidal fracture), has a glassy luster, and is chemically very resistant to weathering. It can be clear, white, gray, pink, or purple. Because quartz resists weathering so well, it accumulates in sand — most beach sand is largely quartz.
Micas are sheet silicates with perfect cleavage in one direction, allowing them to split into thin, flexible, transparent flakes. Pearly luster. Hardness 2.5–4.
Muscovite: colorless to light brown; found in many rock types. Biotite: dark brown to black; contains iron and magnesium.
Both groups are dark-colored silicates found in dark igneous rocks like basalt and gabbro. They contain iron, magnesium, and calcium. The most reliable way to tell them apart is cleavage angle: pyroxenes cleave at nearly 90°; amphiboles cleave at about 60° and 120°.
Augite is the common pyroxene — dark green to black. Hornblende is the common amphibole — black with the distinctive angled cleavage.
Olivine is a green silicate mineral with iron and magnesium; it is very common in Earth's upper mantle and in dark igneous rocks. No cleavage; fractures irregularly. Gem-quality olivine is called peridot.
Calcite (CaCO₃) is the main mineral in limestone and marble. Mohs 3; three cleavage directions forming a rhombohedron; fizzes in acid; often clear to white.
Clay minerals are sheet silicates that form when feldspars and other silicates weather chemically. Extremely fine-grained, earthy luster. Critical components of soil. Kaolinite, montmorillonite, and illite are common types.
Work through properties in a logical sequence: (1) observe luster — metallic or nonmetallic? (2) test hardness — can a fingernail, coin, knife, or glass scratch it? (3) observe cleavage or fracture; (4) test streak; (5) observe color; (6) consider special properties; (7) consider the rock context — what kind of rock was this found in? No single property identifies most minerals; the combination narrows the possibilities.
| Mineral | Luster | Hardness | Cleavage/Fracture | Distinguishing Features |
|---|---|---|---|---|
| Quartz | Glassy | 7 | Conchoidal fracture, no cleavage | Very hard; cannot be scratched by glass |
| Orthoclase feldspar | Glassy | 6 | 2 directions, 90° | Pink to salmon color; no striations |
| Plagioclase feldspar | Glassy | 6 | 2 directions, 90° | White-gray; fine striations on cleavage face |
| Muscovite mica | Pearly | 2.5 | 1 direction, perfect sheets | Colorless to light brown; flexible flakes |
| Biotite mica | Pearly | 2.5–3 | 1 direction, perfect sheets | Dark brown to black; flexible flakes |
| Augite (pyroxene) | Glassy | 5–6 | 2 directions, ~90° | Dark green to black; nearly perpendicular cleavage |
| Hornblende (amphibole) | Glassy | 5–6 | 2 directions, 60°/120° | Black; angled cleavage intersection |
| Olivine | Glassy | 6.5–7 | No cleavage; irregular fracture | Olive green; found in dark igneous rocks |
| Calcite | Glassy | 3 | 3 directions, rhombohedron | Fizzes in acid; double refraction |
| Clay minerals | Earthy/dull | 1–2 | Very fine-grained | Soft; forms from feldspar weathering; sticky when wet |
Ore minerals contain elements — usually metals — in concentrations high enough to be worth extracting economically. A mineral deposit becomes an ore when three conditions are met: it contains a useful material; the concentration (ore grade) is high enough to make extraction practical; and the cost of extraction is less than the value of what is recovered.
| Metal | Primary Ore Mineral(s) | Key Uses |
|---|---|---|
| Iron | Hematite (Fe₂O₃), magnetite (Fe₃O₄) | Steel — most widely used metal on Earth |
| Copper | Chalcopyrite (CuFeS₂), malachite | Electrical wiring, plumbing, electronics |
| Aluminum | Bauxite (aluminum hydroxide minerals) | Lightweight structures, packaging, transportation |
| Lead | Galena (PbS) | Batteries; restricted due to toxicity |
| Zinc | Sphalerite (ZnS) | Galvanizing steel to prevent rust |
| Gold/Silver | Native gold; various sulfides | Electronics, jewelry, currency |
Some minerals are prized for beauty and rarity. Diamond is pure carbon in a cubic crystal structure — the hardest natural material. Corundum forms ruby (red, from chromium impurities) and sapphire (blue, from titanium and iron). Beryl forms emerald (green, from chromium) and aquamarine (blue). Others include tourmaline, topaz, garnet, opal, and turquoise.
| Mineral | Key Use(s) |
|---|---|
| Gypsum | Drywall, plaster, cement additive |
| Halite | Food preservation, road deicing, chemical manufacturing |
| Calcite / limestone | Cement, concrete, agriculture (soil pH adjustment) |
| Quartz | Glass, electronics, concrete, abrasives |
| Feldspar | Ceramics, glass production |
| Talc | Cosmetics, paper, rubber (softest mineral) |
| Fluorite | Steel production, hydrofluoric acid manufacturing |
| Phosphate minerals | Fertilizer production (essential for agriculture) |
The connection between minerals and everyday technology is far more direct than most people realize. Modern society depends on a surprisingly diverse set of mineral resources, many mined in small quantities but used in critical applications.
| Material | Source Mineral / Deposit | Technology Use |
|---|---|---|
| Lithium | Spodumene, lepidolite | Rechargeable batteries (phones, laptops, EVs) |
| Cobalt | Byproduct of Cu/Ni mining | Battery cathodes, high-strength alloys |
| Rare earth elements | Bastnäsite, monazite | Electric motors, wind turbines, screens, lighting |
| Silicon | Quartz (SiO₂) | Computer chips, solar panels |
| Copper | Chalcopyrite and others | All electrical systems |
| Indium / gallium | Byproducts of Zn/Al smelting | Solar panels, LED lighting, fiber optics |
| Phosphate | Phosphate minerals | Fertilizer (essential for global food production) |
| Calcium / fluoride | Calcite, fluorite | Bone, teeth, toothpaste |
Despite their name, most rare earth elements are not especially rare in Earth's crust overall. The challenge is that they are rarely concentrated into easily mineable deposits. China currently produces the majority of the world's rare earth supply, which creates geopolitical and supply-chain concerns for countries that depend on these materials for clean energy technology.
Every mineral on this list had to be found, extracted, processed, and transported. Each step has environmental consequences. Understanding minerals as Earth materials means also understanding them as parts of larger human systems — economic, technological, political, and environmental. These connections are explored further in Chapters 26 and 27.
| Mining Method | How It Works | Typical Use |
|---|---|---|
| Open-pit | Large stepped pits at surface; enormous waste rock volumes | Copper, iron, gold, coal |
| Underground | Tunnels and shafts to deeper ore bodies; smaller surface footprint | Gold, silver, deep coal seams |
| Placer | Separates dense minerals from stream sediments using water | Gold, tin, diamonds |
| Strip | Removes overlying soil and rock (overburden) to access shallow deposits | Surface coal, phosphate, some metals |
When sulfide minerals like pyrite (FeS₂) are exposed to air and water, they react to form sulfuric acid. This acidic water dissolves heavy metals from surrounding rock and drains into nearby streams and groundwater — making water highly acidic and toxic to aquatic life. Acid drainage can continue for decades or centuries after a mine closes because the chemical reactions do not stop when mining does.
| Environmental Impact | Description |
|---|---|
| Habitat destruction | Mines, waste rock piles, roads, and processing facilities directly destroy vegetation, soil, and wildlife habitat |
| Acid mine drainage | Sulfide mineral oxidation produces sulfuric acid that contaminates streams and groundwater |
| Tailings contamination | Crushed rock waste may contain toxic metals and processing chemicals; tailings pond failures can release contaminated material into rivers |
| Water use | Many processing methods require large water volumes; mining in arid regions can compete with agriculture and communities |
| Land subsidence | Underground mine collapse causes uneven ground surface sinking |
| Dust and air quality | Metal dust and particulates affect worker and community health near mines |
A cross-section of a mountain showing an open-pit mine, an underground mine shaft, a tailings pond, and a stream. Arrows indicate pathways of acid drainage from exposed sulfide minerals in waste rock → groundwater → stream. Annotations label: waste rock pile, overburden, ore body, tailings storage area, groundwater table, and a reclamation zone where vegetation is being restored on a completed section.
Modern mining regulations in many countries require reclamation — reshaping the land, replacing topsoil, revegetating, and managing drainage after mining is complete. Remediation addresses contamination that has already occurred: treating acid drainage, stabilizing tailings, and removing contaminated soil.
The effectiveness of reclamation varies. Some landscapes recover substantially; others remain altered for generations. Abandoned historical mines — especially from periods before environmental regulation — remain sources of contamination worldwide.
Recycling reduces, though cannot eliminate, pressure on new mining. Recycling aluminum uses about 5% of the energy required to refine it from bauxite. Recovering rare earth elements from electronic waste is technically challenging but increasingly important. Growing populations and new technologies continue to generate new demand for primary mineral extraction even as recycling rates improve.
Mineral extraction often occurs in communities that receive economic benefits (jobs, tax revenue) but also bear environmental costs (water contamination, air quality, land disturbance). These impacts are not always equally distributed across society — an issue that Earth and environmental scientists, planners, and policymakers all must consider. The growing global demand for technology minerals (lithium, cobalt, copper, rare earth elements) driven by clean energy transition creates new pressure on mineral deposits and new questions about where extraction will occur and under what conditions.
Four diagrams showing the silicate tetrahedron and how tetrahedra link: isolated (olivine), single chain (pyroxene), double chain (amphibole), and sheet (mica). Labels connect each structure to the resulting physical properties — especially why sheet structure produces perfect one-directional cleavage in mica.
Six geometric crystal forms: cubic (halite), hexagonal (quartz), monoclinic (gypsum), orthorhombic (topaz), tetragonal (zircon), and triclinic (kyanite). Each diagram shows the geometric shape and labels the mineral example and its distinctive angles and axes.
A branching decision tree beginning with "Is luster metallic?" Two paths lead through hardness, streak, and cleavage tests to narrow possibilities down to specific minerals. Example branches: metallic + black streak + heavy + cubic cleavage → galena; nonmetallic + glassy + no cleavage + hard (scratches glass) → quartz.
Two side-by-side illustrations: mica splitting into flat, parallel sheets (perfect one-directional cleavage) and a quartz crystal broken with curved conchoidal surfaces (fracture). Labels distinguish flat reflective planes from irregular curved surfaces.
Vertical bar showing 1–10 with reference minerals and comparison objects. Fingernail (~2.5), copper coin (~3), steel knife (~5.5), glass plate (~5.5) all marked. Caption emphasizes this is a relative, not absolute, scale.
Cross-section of a mountain with open-pit mine, underground shaft, tailings pond, and stream. Arrows show acid drainage pathways from sulfide minerals → groundwater → stream. Annotations label waste rock, overburden, ore body, tailings storage, groundwater table, and reclamation zone.
Use the properties given to identify each mineral. Explain which two or three properties were most decisive in your identification.
| Mineral | Luster | Hardness | Streak | Cleavage | Density (g/cm³) |
|---|---|---|---|---|---|
| Quartz | Glassy | 7 | White | None (conchoidal fracture) | 2.65 |
| Orthoclase feldspar | Glassy | 6 | White | 2 directions, 90° | 2.56 |
| Calcite | Glassy | 3 | White | 3 directions, rhombohedron | 2.71 |
| Galena | Metallic | 2.5 | Gray-black | 3 directions, cubic | 7.6 |
| Pyrite | Metallic | 6–6.5 | Greenish-black | Poor | 5.0 |
| Hematite | Metallic to earthy | 5.5–6.5 | Red-brown | None | 5.3 |
| Magnetite | Metallic | 5.5–6 | Black | None | 5.17 |
| Muscovite mica | Pearly | 2.5 | White | 1 direction, perfect | 2.83 |
| Halite | Glassy | 2.5 | White | 3 directions, cubic | 2.16 |
| Gypsum | Pearly/silky | 2 | White | 3 directions | 2.31 |
Fact: Pyrite does have a golden color and metallic luster. However, pyrite has a greenish-black streak, a hardness of 6–6.5 (much harder than gold at ~2.5), and forms cubic crystal faces. Real gold has a yellow streak, is very soft, and has a density of 19.3 g/cm³ — about four times denser than pyrite. A single streak test or hardness test eliminates the confusion immediately.
Fact: The most abundant minerals — feldspar, quartz, mica, calcite — make up most of the rocks at Earth's surface. Most beach sand is largely quartz. Rarity makes some minerals valuable, but the most geologically important minerals are the ordinary, widespread ones.
Fact: A mineral is a specific substance with a defined composition and crystal structure. A rock is a mixture of one or more minerals — or sometimes organic material. Granite is a rock; the quartz, feldspar, and mica inside it are minerals. The distinction matters because rocks and minerals have different properties, form differently, and are studied differently.
Fact: A hard mineral resists scratching; a tough material resists breaking. Diamond is the hardest mineral — nothing scratches it — but diamond can be broken or shattered by a sharp blow because its crystal structure has cleavage planes. Jade is much less hard than diamond but exceptionally tough because of its interlocking crystal microstructure.
Fact: Mining does cause significant environmental impacts, including habitat destruction, water contamination, and land disturbance. However, the minerals extracted by mining are essential for infrastructure, technology, medicine, and agriculture — including for clean energy systems that reduce other environmental impacts. Evaluating mining decisions requires weighing specific environmental costs against specific social and economic benefits — a judgment that depends on evidence, not blanket approval or disapproval.
Chapter 6 studies igneous rocks — rocks formed by the cooling and solidification of molten material. You already know from Section 5.3 that minerals crystallize from magma; Chapter 6 examines how the rate of cooling, the composition of magma, and the location of cooling (underground or at the surface) determine which minerals form and what kind of rock results. You will connect igneous rocks to plate tectonics, volcanic landforms, and natural hazards. The minerals you identified in Chapter 5 — especially quartz, feldspar, mica, pyroxene, amphibole, and olivine — are the building blocks of nearly every igneous rock. Knowing them well will make igneous rock identification straightforward.