Mohs 1–10: Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Corundum Diamond. 'The Girls Can Flirt...'
Mohs Hardness Scale
The classic 1–10 mineral hardness scale — and the mnemonic that makes it permanent
Full mnemonic: 'The Girls Can Flirt And Other Queer Things Can Do' — Talc (1), Gypsum (2), Calcite (3), Fluorite (4), Apatite (5), Orthoclase/Feldspar (6), Quartz (7), Topaz (8), Corundum (9), Diamond (10). Mohs scale is relative (ordinal), not linear — diamond is ~1,500× harder than corundum in absolute terms. Fingernail ≈ 2.5, copper penny ≈ 3, glass ≈ 5.5, steel file ≈ 6.5. Hardness test: scratch unknown mineral with known one. Industrial: diamond (cutting), corundum (sandpaper/rubies/sapphires), quartz (glass/electronics).
The systematic properties used to identify any mineral — without a chemistry lab
Color: unreliable alone (quartz can be clear, purple, pink, white). Streak: color of powder on unglazed porcelain — diagnostic (hematite: red-brown streak regardless of surface color). Luster: metallic vs non-metallic (vitreous/glassy, resinous, pearly, silky, adamantine/diamond). Hardness: Mohs test. Cleavage: flat breaks along atomic planes — number of directions and angles (mica: 1 direction perfect; halite: 3 at 90°). Fracture: conchoidal (quartz), hackly. Specific gravity: density relative to water. Special properties: magnetism (magnetite), effervescence with HCl (calcite), fluorescence (fluorite), taste (halite).
Color
Unreliable alone
Luster
Metallic vs non-metallic
Hardness
Mohs scratch test
Streak
Powder color — more reliable
Cleavage
Flat breaks along planes
Specific gravity
Density vs water
Silicates
Silicates: SiO₄ tetrahedra — isolated, chains, sheets, frameworks. 90% of Earth's crust. Quartz = 3D framework.
Silicate Minerals
The dominant mineral group in Earth's crust — built from the silicon-oxygen tetrahedron
SiO₄ tetrahedron: 4 oxygen around 1 silicon — fundamental building block. Structures: isolated (olivine, garnets — nesosilicates), single chain (pyroxenes), double chain (amphiboles), sheet (micas, clay minerals), framework (quartz, feldspars — every Si-O shared). Framework silicates are most stable/common. Feldspars: most abundant mineral group in crust — plagioclase (Na-Ca) and K-feldspar. Quartz: pure SiO₂, very common, resistant to weathering. Micas: perfect basal cleavage (sheet structure). Olivine: mantle mineral, least stable, weathers first (Bowen's Series).
The most diagnostic physical property of many minerals — how they break
Cleavage: preferential breakage along planes of weak atomic bonding. Number of directions: mica (1), feldspar and calcite (2–3), halite (3 at 90°). Angles between cleavage planes: diagnostic. Calcite: 3 cleavage at 75° → rhombohedra. Halite: 3 at 90° → cubes. Amphibole vs pyroxene: both have 2 cleavages, but angle differs (amphibole ~60/120°, pyroxene ~90°) — diagnostic for thin section. Fracture types: conchoidal (quartz, obsidian — curved shell-like), hackly (native metals), uneven/irregular. Obsidian cleavage: none (fractures conchoidally — sharp edges, used as cutting tools).
Bowen's Reaction Series
Bowen's Series: olivine → pyroxene → amphibole → biotite → K-feldspar → muscovite → quartz. First in, first to weather.
Bowen's Reaction Series
The order in which minerals crystallize from cooling magma — and why it also predicts weathering sequence
N.L. Bowen (1922): two branches crystallizing from basaltic magma. Discontinuous branch (iron/magnesium): olivine → pyroxene → amphibole → biotite (each replaces previous as temp drops). Continuous branch: Ca-plagioclase → Na-plagioclase (composition shifts as temp drops). Both converge at K-feldspar → muscovite → quartz (last to crystallize, most stable at surface). Goldich Dissolution Series: minerals crystallizing FIRST (high temp, deep) are LEAST stable at surface → weather first. Quartz: crystallizes last, most stable — forms beach sand. Olivine: weathers fastest.
How minerals form — four processes that create all natural inorganic compounds
Magmatic: crystallize from cooling melt — silicates (Bowen's Series). Temperature determines which minerals form. Hydrothermal: hot water (100–500°C) carries dissolved minerals → precipitate in fractures as water cools. Many ore deposits (gold, copper, silver veins). Sedimentary: evaporation (halite, gypsum), biochemical precipitation (calcite in shells → limestone), chemical (chert, BIF). Weathering: decomposition of existing minerals → clay minerals. Metamorphic: existing minerals recrystallize under heat + pressure without melting → new minerals (garnet, staurolite, kyanite, sillimanite index minerals of metamorphic grade).
Native Elements
Native elements: pure single-element minerals. Gold, silver, copper, sulfur, graphite, and diamond are all native elements.
Native Elements
Minerals made of just one element — from precious metals to graphite and diamond
Native metals: gold (Au, inert — never tarnishes, found in streams and veins), silver (Ag, tarnishes), copper (Cu, oldest metal smelted ~7000 BCE), platinum (rare, high melting point). Native nonmetals: sulfur (yellow, around volcanic vents), diamond (C, cubic, hardest), graphite (C, hexagonal, softest conductor — same element as diamond, different crystal structure). Carbon allotropes: diamond (sp³ bonds, 3D framework → hardest) vs graphite (sp² bonds, flat sheets → soft, conducts electricity). Bismuth, arsenic, antimony also occur as native elements. Native elements ≈ 20 minerals — small group but highly valuable.