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Sedimentary rocks

Sedimentary rocks. Formed in seas and lakes. Formation. Rock materials Derived from weathering and erosion Are transported by river / wind And later deposited (sedimentation) Under the pressure of the overlying sediment These materials are hardened into solid rock.

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Sedimentary rocks

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  1. Sedimentary rocks Formed in seas and lakes

  2. Formation • Rock materials • Derived from weathering and erosion • Are transported by river / wind • And later deposited (sedimentation) • Under the pressure of the overlying sediment • These materials are hardened into solid rock

  3. Characteristics of sedimentary rocks • Non-crystalline • Stratified (layered) • Bedding planes between rock strata • May contain fossil

  4. Conglomerate

  5. Characteristics • Rock containing rounded pebbles • they are cemented by fine groundmass • It is more resistant • Their outcrop across stream beds may produce waterfalls and rapids

  6. Breccia

  7. Characteristics • The rock contains angular fragments

  8. Breccia – Ap Chau

  9. Folding in sedimentary rocks

  10. Ammonite fossil

  11. Sandstone

  12. Sandstone

  13. Characteristics • Sand grains are cemented • Deposited farther away from the coast • Less resistant than conglomerate and breccia

  14. Siltstone

  15. Stratification in shale e.g.Tung Ping Chau

  16. Siltstone layer being eroded to form a sea arch, Tai O.

  17. Characteristics • Very fine sediment of silt and mud is deposited and cemented together on sea floor far away from coast • Made up of numerous thin layers (stratified structure) • It is not resistant to weathering and erosion

  18. Cross-bedding in siltstone

  19. Faulting in siltstone

  20. Igneous rocks - Volcanic rocks Ash, pyroclasts and lava flows

  21. Flowlines in rhyolite

  22. Columnar jointing due to cooling of lava - rhyolite

  23. Coarse tuff

  24. Characteristics • Ash and pyroclastic materials ejected during volcanic eruption • Presence of volcanic bombs

  25. Volcanic bombs

  26. Igneous rocks - Hypabyssal rocks In sills and dykes

  27. Dolerite dyke

  28. Dolerite

  29. Feldspar porphyry

  30. Igneous rocks In batholith

  31. 3 sets of joints in granite

  32. Granite

  33. Badland landscape

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