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

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

Conglomerate

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

Breccia

Characteristics  The rock contains angular fragments

Breccia – Ap Chau

Folding in sedimentary rocks

Ammonite fossil

Sandstone

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

Siltstone

Stratification in shale e.g.Tung Ping Chau

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

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

Cross-bedding in siltstone

Faulting in siltstone

Igneous rocks - Volcanic rocks Ash, pyroclasts and lava flows

Flowlines in rhyolite

Columnar jointing due to cooling of lava - rhyolite

Coarse tuff

Characteristics  Ash and pyroclastic materials ejected during volcanic eruption  Presence of volcanic bombs

Volcanic bombs

Igneous rocks - Hypabyssal rocks In sills and dykes

Dolerite dyke

Dolerite

Feldspar porphyry

Igneous rocks In batholith

3 sets of joints in granite

Granite

Badland landscape