Download Rocks types

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
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