M3 Earth Science

Mineral Basics

  • Minerals: natural, inorganic, solid, definite chemical composition, and an ordered internal structure.

  • Rock-forming minerals are the most common minerals in Earth's crust (e.g., Feldspar, Quartz, Amphibole, Mica, Olivine, Garnet, Calcite, Pyroxene).

  • Rocks are aggregates of minerals; rocks form when minerals are glued together by natural processes.

  • Lithosphere: the rigid outer shell of Earth (crust + upper mantle). "Lithos" means stone.

Key Concepts: Mineral Properties and Identification

  • Color vs. Streak

    • Color can vary due to impurities; streak (the color of powdered mineral) is more diagnostic.

    • Example: hematite can be red-brown in color but leaves a red-brown streak.

  • Luster

    • Metallic vs. non-metallic; non-metallic subtypes include vitreous (glassy), pearly, resinous, silky, greasy, adamantine, etc.

  • Hardness

    • Measured on the Mohs scale from 1 (softest) to 10 (hardest).

    • Common reference minerals: Talc (1), Gypsum (2), Calcite (3), Fluorite (4), Apatite (5), Feldspar (6), Quartz (7), Topaz (8), Corundum (9), Diamond (10).

  • Cleavage vs. Fracture

    • Cleavage: breaks along flat, parallel planes due to weak bonding.

    • Fracture: breaks along irregular surfaces (conchoidal, fibrous, hackly, uneven).

  • Streak, Color, Luster, Hardness, Cleavage, Fracture, Crystal Form/Habit, Specific Gravity, Magnetism, Taste, Double Refraction, Effervescence, Fluorescence, Phosphorescence, Triboluminescence.

  • Specific Gravity (density relative to water)

    • Definition: the ratio of a mineral’s weight to the weight of an equal volume of water.

    • Formula: SG = rac{W{ ext{mineral}}}{W{ ext{water}}} \ ext{Equivalently } SG \,=\, \frac{\rho{ ext{mineral}}}{\rho{water}} \approx \rho_{ ext{mineral}}

  • Crystal Form/Habit

    • External shape of a crystal or group of crystals; reflects internal structure.

  • Special properties (Table 1.3 in course): magnetism, taste, double refraction, effervescence with acid, fluorescence/phosphorescence, triboluminescence.

Mineral Classification by Composition

  • 7 major mineral groups:

    • Silicates (most abundant in crust; SiO$_4^{4-}$ tetrahedra)

    • Oxides

    • Sulfides

    • Sulfates

    • Carbonates

    • Halides

    • Native Elements

  • Examples:

    • Silicates: quartz (SiO$_2$), feldspar, mica, amphibole, pyroxene, olivine, garnet.

    • Oxides: magnetite (Fe$3$O$4$), hematite (Fe$2$O$3$).

    • Sulfides: galena (PbS), pyrite (FeS$_2$).

    • Sulfates: gypsum (CaSO$4$·2H$2$O), barite (BaSO$_4$).

    • Carbonates: calcite (CaCO$3$), dolomite (MgCO$3$·CaCO$_3$).

    • Halides: halite (NaCl), fluorite (CaF$_2$).

    • Native Elements: gold (Au), sulfur (S), graphite (C).

Common Rock-Forming Minerals

  • Common rock-forming minerals include: Feldspar, Quartz, Amphibole, Mica, Olivine, Garnet, Calcite, Pyroxene.

  • About seven of the eight rock-forming minerals are silicates.

The Rock Cycle: Overview

  • Rocks are classified by formation process into three main types: Igneous, Sedimentary, Metamorphic.

  • Igneous rocks form by cooling and solidification of magma/lava.

  • Sedimentary rocks form by accumulation, lithification, and cementation of sediments.

  • Metamorphic rocks form when existing rocks are altered by heat and/or pressure (metamorphism).

  • Protolith: the parent rock from which a metamorphic rock forms.

Igneous Rocks: Formation and Textures

  • Formation modes:

    • Intrusive (plutonic): cooling below the surface; large visible crystals; phaneritic texture.

    • Extrusive (volcanic): cooling at/above surface; fine crystals or glassy texture; aphanitic or glassy texture.

    • Porphyritic: both large crystals (phenocrysts) and a fine-grained groundmass.

    • Pyroclastic/volcanic debris: formed from explosive eruptions (igneous but with fragmented material).

  • Common textures:

    • Phaneritic: visible crystals (intrusive).

    • Aphanitic: no visible crystals (extrusive).

    • Porphyritic: mixed crystal sizes.

    • Glassy: no minerals, natural glass (obsidian).

    • Vesicular: gas bubbles preserved in rock.

  • Composition-based categories (color index):

    • Felsic: light-colored, high SiO$_2$, lower Fe/Mg.

    • Intermediate: mix of light/dark minerals.

    • Mafic: darker colors, higher Fe/Mg, lower SiO$_2$.

    • Ultramafic: very low SiO$_2$, very high Fe/Mg.

  • Environment of formation (diagrammatic): Continental vs Oceanic; mantle sources; plutonic vs volcanic.

  • Common igneous rocks (examples): granite, diorite, gabbro (intrusive); rhyolite, andesite, basalt (extrusive/volcanic); obsidian (glassy); pumice (vesicular).

Sedimentary Rocks: Formation and Types

  • Formation processes: weathering, erosion, dissolution, precipitation, deposition, lithification (compression + cementation).

  • Texture types:

    • Clastic (mechanical): formed from cemented fragments of other rocks (sandstone, shale, conglomerate, breccia, siltstone).

    • Crystalline/Chemical (non-clastic): formed by precipitation of minerals from water (limestone, rock salt, gypsum, dolostone).

    • Bioclastic/Organic: formed from plant/animal remains (coal, some limestones, chert).

  • Sedimentary features: fossils, stratification/bedding.

  • Clast size hierarchy: gravel, sand, silt, clay; clasts may be rounded or angular (breccia vs. conglomerate).

  • Major sedimentary rocks: sandstone, shale, conglomerate, breccia, limestone, coquina, chalk, dolostone, gypsum, halite, coal.

Metamorphic Rocks: Formation and Textures

  • Metamorphism requires heat and/or pressure; rocks may be recrystallized and mineralogy may change.

  • Protolith transforms under heat/pressure to form metamorphic rocks; differential stress can create foliation.

  • Texture types:

    • Foliated: minerals aligned parallel to pressure direction (slaty, phyllitic, schistose, gneissic textures).

    • Non-foliated: minerals recrystallize without alignment (e.g., marble from limestone; quartzite from sandstone).

  • Metamorphic grade reflects degree of metamorphism (low to high): slate, phyllite, schist, gneiss (foliated); marble, quartzite (non-foliated).

  • Examples of metamorphic relationships: sandstone → quartzite; shale → slate → phyllite → schist → gneiss; limestone → marble.

Quick Reference: Rock Identification Flow (conceptual)

  • Start with texture: foliated vs non-foliated (metamorphic) or crystal size (igneous)

  • Then consider composition: felsic vs mafic (igneous) or sedimentary composition (clastic vs chemical vs organic)

  • Environment of formation and parent rock help refine rock type and name

Quick Facts for Last-Minute Review

  • Minerals define rocks; rocks are aggregates of minerals glued by natural processes.

  • Color alone is not reliable for mineral ID; use streak, hardness, cleavage, luster, and other properties.

  • The Mohs scale is a qualitative hardness scale from 1 to 10.

  • Silicates dominate the rock-forming minerals due to the abundance of Si and O in crust.

  • The rock cycle describes how rocks continuously transform among igneous, sedimentary, and metamorphic forms through cooling, weathering, lithification, and metamorphism.

Equations and Key Values (quick reference)

  • Specific Gravity: SG = \frac{W{mineral}}{W{water}} = \frac{\rho{mineral}}{\rho{water}} \approx \rho_{mineral}

  • Mohs hardness reference (ordered): 1 Talc, 2 Gypsum, 3 Calcite, 4 Fluorite, 5 Apatite, 6 Orthoclase Feldspar, 7 Quartz, 8 Topaz, 9 Corundum, 10 Diamond