Minerals, Rocks and Geological Resources
This domain tests identification and classification of minerals and rocks, the processes that form them, and the economic and sustainability questions attached to mining and energy resources. Identification questions reward systematic observation: composition first, texture second, origin third.
Minerals
- Diagnostic properties: hardness (Mohs 1 talc to 10 diamond), cleavage versus fracture, lustre, streak, colour, specific gravity, reaction with dilute acid (calcite effervesces).
- Silicate frameworks: nesosilicates (olivine), inosilicates (pyroxene, amphibole), phyllosilicates (micas, clays), tectosilicates (quartz, feldspars). More polymerised frameworks are more resistant to weathering.
- Bowen's reaction series explains crystallisation order and, read backwards, weathering stability: olivine, pyroxene, amphibole, biotite, feldspars, muscovite, quartz.
Rocks
- Igneous: plutonic (phaneritic) versus volcanic (aphanitic, porphyritic, vesicular); classified by silica - acid, intermediate, basic, ultrabasic - with granite, granodiorite, andesite, basalt and peridotite as the reference names.
- Sedimentary: detrital (conglomerate, sandstone, shale), chemical (limestone, gypsum, halite), biochemical (coal, chert).
- Metamorphic: foliated (slate, schist, gneiss from a shale protolith) and non-foliated (marble from limestone, quartzite from sandstone). Facies series record pressure and temperature: greenschist, amphibolite, granulite, blueschist, eclogite.
Resources and sustainability
Metallic ores (Fe, Cu, Pb–Zn, Au), industrial minerals, evaporites, aggregates and energy resources. Catalonia's examples: the Cardona salt diapir with halite and potash, the Bages potash mines, Berguedà coal basins now closed, Garraf and Montjuïc limestones historically used as building stone and cement raw material. Sustainability issues: finite reserves, acid mine drainage, tailings dams, land restoration, and the conflict between extraction and protected areas.
Worked example
A coarse-grained rock contains about 35% quartz, 30% alkali feldspar, 25% plagioclase and 10% muscovite. Reasoning: coarse grain size means slow cooling at depth (plutonic); quartz plus two feldspars plus muscovite indicates a silica-rich, peraluminous melt derived from continental crust; muscovite stability requires water-rich magma. Identification: granite. Follow-up: it will weather to quartz sand plus clay, and it is not a good reservoir or aggregate source because of its coarse, fractured texture.
Traps that cost marks
Using colour as the main criterion (mafic minerals can be dark, but texture and composition decide); confusing cleavage with crystal shape; calling marble a sedimentary rock; labelling any shale-derived metamorphic rock as gneiss without evidence of banding.