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AS-A level Geology

Learn about the different ways minerals form, including solidification, hydrothermal activity, recrystallization, evaporation, cementation, and chemical weathering.

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AS-A level Geology

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  1. AS-A level Geology Mineral Forming Processes Click anywhere on the screen to move on

  2. Minerals form in 6 different ways • Solidification • Hydrothermal Activity • Recrystallisation • Evaporation • Cementation • ChemicalWeathering Mineral Forming Processes – S.H.R.E.C.C.

  3. Solidification (crystallisation) from a molten state from Lava or Magma Cornish Granite Shap Granite Forms the silicate minerals making up igneous rocks and includes quartz, feldspars, micas, augite and olivine

  4. Hydrothermal Activity Groundwater is heated by igneous plutons to between 50°C and 400°C Hot water dissolves out trace amounts of metals from large volume of rock as it travels along bedding planes, joints, laminations, faults, cleavages and pore spaces As these hot waters cool they precipitate the metals in veins and lodes in a more concentrated form. Examples include galena (lead ore) and haematite (iron ore) Haematite

  5. Hydrothermal activity along the Mid Atlantic Ridge Hydrothermal fluids at 350°C Seawater at 2°C to 4°C Chimneys can grow to over 30 metres high Results in the formation of chimneys of massive sulphide minerals such as chalcopyrite, galena and sphalerite

  6. Metamorphic Recrystallisation Calcite recrystallises when limestone is heated, forming marble. Heat and pressure turn clay minerals (in shale) into garnet and mica in a schist.

  7. Evaporation of Saline Water Seawater contains an average of 3.5% dissolved solids

  8. Evaporation of Saline Water As seawater evaporates the concentration of dissolved solids progressively increases

  9. Evaporation of Saline Water Salt deposits (halite) Death Valley, California Calcite, gypsum and halite can be precipitated from solution following evaporation of a shallow body containing saline water e.g a shallow sea or an inland lake

  10. Precipitation as a Cement Precipitation of minerals as a cement from pore water during diagenesis and lithification Quartz, calcite or haematite may be precipitated around existing grains filling pore spaces in sedimentary rocks Haematite cement coating quartz grains

  11. Chemical Weathering of Silicate Minerals to form Clay Minerals Water reacts with silicate minerals in the process of hydrolysis and converts them into clays with ions released into solution Feldspar forms China Clay Biotite Mica forms Chlorite Olivine forms Serpentine Only Quartz is unaffected China Clay (Kaolinite)

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