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Minerals and rocks flashcards

Mineral Criteria and Examples

  • Minerals are defined by a set of criteria used in geology:
    • They must be a solid state at ordinary conditions.
    • They must be naturally occurring (not man-made).
    • They must be inorganic (not formed by life processes in the object sense).
    • They must have an orderly internal structure (a crystal lattice).
    • They must have a specific chemical composition (which can include impurities that alter color or properties).
  • Example discussions:
    • Ice is a mineral because it is solid, natural, inorganic, has an orderly structure, and a definite composition H_2O. When it melts, it is no longer a mineral.
    • Water (liquid) is not a mineral; ice (solid) is.
  • Thin sections and scale in mineral study:
    • To study rocks at a finer level, we use thin sections prepared to about 4\ \mu m thickness and viewed under a microscope.
    • This is similar to viewing biological slides or blood smears under a microscope to reveal crystal grains and mineral boundaries.
  • Scale concept in geology:
    • From satellite imagery and maps to field observations and micro-scale thin sections, scale is essential for understanding rock-forming processes and mineral textures.
    • Example: Yosemite Valley can be observed at multiple scales to infer rock types and grain sizes.
  • Practical observations:
    • We may observe individual grains or minerals in rocks, or only a fine-grained matrix where crystals are not visible to the naked eye.
    • Some rocks appear as a mosaic of interlocking crystals; others are composed of clastic grains cemented together.

Crystalline Rocks vs Clastic Rocks

  • Crystalline rocks:
    • Contain visible crystals and intergrown minerals; crystals may be large or very small (viewable with a hand lens or microscope).
    • Tend to show a solid crystalline texture and may appear as one continuous crystal or as a mosaic of crystals.
    • Amethyst, quartz, calcite crystals are common examples.
  • Clastic rocks:
    • Composed of fragments (clasts) of other rocks that have been weathered and transported, then lithified (cemented together).
    • Tend to show layering or a clastic texture with individual grains recognizable at some scale.
    • Think of a snowball-like aggregation where grains are pressed together.
  • Visual cues:
    • Crystalline rocks often lack distinct layering; clastic rocks tend to show bedding or layering from sediment deposition.
  • Notable crystal imagery:
    • Amethyst and quartz show well-formed crystals in crystalline rocks.
    • Citrine is another crystal form related to quartz.

Observing Minerals under Magnification and Typologies

  • Mineral identification approaches:
    • Crystal form and habit: different minerals crystallize in characteristic shapes, but color alone is not a reliable identifier due to impurities.
    • Luster: the shininess or dullness of a mineral surface.
    • Hardness: resistance to scratching; commonly assessed on the Mohs scale (from 1 to 10; 10 is the hardest).
    • Streak: the color of a mineral’s powder when rubbed on an unglazed porcelain plate. Not all minerals have a streak.
    • Magnetism: some minerals (e.g., magnetite) are magnetic.
    • Density (specific gravity): a measure of how heavy a mineral is for its size.
    • Acid tests: acids can react with some minerals; effervescence (CO₂ release) occurs with carbonates like calcite.
  • Key chemical tests and caveats:
    • Carbonates such as calcite and dolomite fizz with acid, helping distinguish them from non-carbonate minerals.
    • Halides (e.g., NaCl) often form cubes or other cleavage patterns due to their crystal lattice.
    • Some minerals show characteristic color variations due to impurities (e.g., diamonds can have blue, brown, or pink hues from trace elements).
  • Practical field and lab notes:
    • Mineral identification kits include various tests (color, luster, hardness, streak, acid reaction, magnetism).
    • In lab settings, prepared slides (thin sections) allow detailed observation of crystal structures and grain boundaries.

Crystal Shapes, Cleavage, and Lattice Structure

  • Three general crystal shapes you should know for this course:
    • Cube-like (octahedral family) – exemplified by halite (sodium chloride) with cubes when it cleaves.
    • Tetrahedron – a triangular pyramid shape common in certain silicates.
    • Octahedron – composed of two interpenetrating tetrahedra.
  • Cleavage (how a mineral breaks along planes):
    • Some minerals have distinct cleavage along parallel planes:
    • One plane of cleavage (tends to peel like a sheet, e.g., muscovite).
    • Two planes of cleavage (often forming a rectangular pattern).
    • Three planes of cleavage (forms a cubic pattern, e.g., halite).
    • No cleavage (breaks irregularly).
    • Examples:
    • Muscovite (one plane of cleavage, peelable sheets).
    • Halite (three planes of cleavage, forms cubic fragments).
    • Calcite and fluorite (varying cleavage patterns; halides and sulfates show characteristic breaks).
  • The role of lattice structure:
    • The arrangement of atoms (bonding and packing) dictates how minerals break and their cleavage directions.
    • Salt (NaCl) shows a clear cubic cleavage because of its cubic lattice geometry.
  • Quick visual cues:
    • Some rocks show large, visible cleavage planes; others reveal more intergrown crystals with less obvious cleavage.

Mineral Chemistry and Bonding in Rocks

  • Key chemical concepts:
    • Elements combine to form minerals through bonds; the type of bonding influences properties.
    • Protons define the element; electrons and electron configuration determine bonding behavior.
    • Shells and orbitals provide the basis for chemical bonding and ion formation.
  • Bonding types and their implications:
    • Covalent bonding (sharing electrons) is the strongest type among common mineral bonds.
    • Ionic bonding (transfer of electrons) and covalent bonding both contribute to mineral strength, but covalent bonds often dominate in silicate frameworks and many crustal minerals.
    • Metallic bonding and van der Waals interactions exist but are weaker in many crystalline minerals.
  • Why covalent bonds matter for weathering:
    • Materials with strong covalent bonds tend to resist weathering and weather more slowly, leaving behind more resistant minerals.
    • Graphite (weak intermolecular bonding) is different from diamond (strong covalent bonds), despite having the same chemical formula C.
    • Diamond can be produced in laboratories by applying high pressure and temperature to graphite, transforming the crystal structure.
  • Water molecule as a case study:
    • Water is held together by covalent bonds in the molecule; this makes hydrogen bonding and energy considerations challenging for hydrogen fuel concepts, since breaking O–H bonds requires substantial energy.
  • Practical bonding examples:
    • The bonding and structure of common minerals determine their hardness and stability in rocks.

Common Mineral Groups and Representative Minerals

  • Silicates (the largest group in crustal rocks):
    • Basic building unit: tetrahedron of (
      SiO_4^{4-}) units.
    • Common silicate minerals:
    • Olivine (green minerals seen in some Sierra Nevada rocks; often forms in high-temperature mafic rocks).
    • Pyroxene and Amphibole (chain and double-chain silicates).
    • Micas: Muscovite and Biotite (sheet silicates with excellent cleavage).
    • Feldspar (two main families: alkali feldspar and plagioclase; feldspars are more resistant to weathering than some other minerals).
    • Quartz (crystalline silica, extremely common and chemically inert).
  • Carbonates (non-silicate, carbonates):
    • Calcite (CaCO₃) and Dolomite (CaMg(CO₃)₂).
    • Carbonates fizz with dilute acid due to CO₂ release.
  • Oxides:
    • Magnetite (Fe₃O₄) and Hematite (Fe₂O₃) – important iron-oxide minerals; often magnetic (magnetite).
  • Halides (evaporites):
    • Halite (NaCl) – evaporite mineral; crystal forms in cubic geometry; cleavage patterns reflect lattice structure.
  • Sulfates and sulfides:
    • Gypsum (CaSO₄·2H₂O) – sulfate; used in plaster; also an evaporite.
    • Pyrite (FeS₂) – fool’s gold; a sulfide with metallic luster.
    • Galena (PbS) – lead sulfide; historically used in cosmetics and pigments, and widely found in desert regions (e.g., Mojave).
  • Native elements and metals:
    • Native copper, gold, and silver exist as minerals in some locales, but not as abundant as silicates or carbonates in crustal rocks.
  • Abbreviated chemical contexts:
    • Common mineral formulas to recognize:
    • Salt/halite: NaCl
    • Calcite: CaCO_3
    • Dolomite: CaMg(CO3)2
    • Quartz: SiO_2
    • Olivine: (general composition includes (Mg,Fe)₂SiO₄)
  • Building-block idea:
    • Silicates and carbonates are the dominant building blocks of rocks; native metals and oxides exist but in smaller abundance compared to crustal silicates and carbonates.

Crustal Abundance and Regional Variations

  • Abundance in Earth’s crust (by typical crustal composition ordering):
    • Oxygen is the most abundant element in the crust.
    • Silicon is the second most abundant; followed by Aluminum.
    • Iron is also abundant and influences density and mineralogy, especially in continental vs. oceanic crust.
  • Continental vs. oceanic crust:
    • Oceanic crust is generally heavier (more Fe and Mg-rich basaltic rocks) and more dense.
    • Continental crust is lighter and richer in silica and aluminum (granitic composition).
  • Implications for rock formation:
    • The surrounding geochemical environment (nutrients, nearby rocks, mantle-derived material) influences which minerals dominate in a given rock.
    • The proximity to tectonic and volcanic processes can alter chemical makeup (e.g., nickel-rich minerals from mantle sources versus lead-rich granitic rocks near the surface).

Atomic Structure, Periodic Table, and Bonding Context

  • Atomic basics:
    • Atoms have protons, neutrons, and electrons.
    • The arrangement of electrons in shells (orbitals) determines bonding propensity and charge.
    • The periodic table lists elements with symbols, atomic numbers (protons), and electron configurations; you generally need to know protons, symbol, and atomic number for most geology contexts.
  • Periodic table practicalities for geology:
    • The teacher emphasizes you do not need to memorize the entire periodic table, but you should be familiar with common elements that form crustal minerals (e.g., Si, O, Al, Fe, Mg, Ca, Na, K, Cl, C, S).
  • Bonding types recap:
    • Covalent bonding (sharing electrons) is the strongest for mineral frameworks and contributes to high hardness and rigidity.
    • Ionic bonding involves transfer of electrons and formation of charged ions; it leads to different crystal structures and cleavage patterns.
    • Metallic bonding and van der Waals forces exist in some minerals but are less central to crustal rock textures than covalent/ionic bonding.

Everyday Geological References in Construction and Objects

  • Common minerals and their practical uses in everyday life:
    • Copper (Cu) wiring and plumbing materials; found in electrical wiring and metal fixtures.
    • Quartz (SiO₂) used in clocks and electronics; quartz is present in many glass and ceramic products; also a component of granite countertops.
    • Granite countertops are composed of minerals such as quartz, feldspar, and mica.
    • Cement and concrete include various minerals and rock aggregates; gypsum (CaSO₄·2H₂O) is used to make wallboard (drywall).
    • Bricks and insulation materials incorporate minerals and rock-derived constituents.
    • Halite (NaCl) forms table salt and evaporite deposits.
    • Piping and metal components may involve iron (Fe), aluminum (Al), copper (Cu), and other minerals.
  • Local geology shaping everyday life:
    • The mineral composition and rock types in a region influence building materials, roadbeds, and infrastructure.
    • Weathering and erosion of covalently bound minerals tend to leave behind more resistant minerals on the surface.

Connections, Implications, and Big Questions

  • Why mineralogy matters:
    • Understanding minerals helps explain rock types, weathering processes, soil formation, and crustal evolution.
    • It informs exploration (where minerals of economic value may be found) and environmental considerations (acid rainfall effects on minerals like calcite).
  • Ethical and practical reflections:
    • The study of minerals connects scientific understanding with practical applications in construction, industry, and resource management.
    • It underscores how the Earth’s interior processes and surface conditions interact to produce the materials we rely on daily.
  • Summary of core ideas:
    • Minerals are solid, natural, inorganic substances with an orderly atomic structure and a defined chemical composition.
    • They can be crystalline or form clastic textures; observation across scales from satellites to thin sections is essential.
    • Identification relies on crystal form, cleavage, luster, hardness, streak, magnetism, density, and chemical tests like acid reactions.
    • Silicates, carbonates, oxides, halides, sulfates, sulfides, and native metals are the main mineral groups; silicates and carbonates are especially abundant in crustal rocks.
    • Bonding (especially covalent vs ionic) controls hardness and weathering; diamond vs graphite illustrates how crystal structure governs properties.
    • The crust’s composition and regional geology drive the distribution of minerals and the materials we use in daily life.