sedimentary rocks formed in seas and lakes. formation rock materials derived from weathering and...

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

Sandstone

Characteristics

Sand grains are cemented Deposited farther away from the coast Less resistant than conglomerate and brecci

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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