Geology and Soil Mechanics FORMATION PROCESSES Rocks can be grouped into three broad classes, depending on their origin. They are-• • •
Igneous. Sedimentary. Metamorphic
CLASSIFICATION OF ROCKS Rocks can be grouped into three broad classes, depending on their origin. They are-• • •
Igneous. (Origin from magma/lavas) Sedimentary. (Weathering/erosion of other rocks) Metamorphic (pressure and heating of rocks)
Classified on TEXTURE/ FABRIC
GRANULAR GRAIN SIZE
ARRANGEMENT CRYSTALLINE
LIGHT
COMPOSITION
MINERAL CONTENT
COLOUR DARK
Geology and Soil Mechanics GRAIN SIZE Grain Size
(mm)
COARSE
>2mm
MEDIUM
2mm- 0.06
Require hand lens to see individual grains/crystals
FINE
>0.06
Individual grains not seen with hand lens
VERY FINE
0.002mm
Grains contained in a matrix
Visual Seen with naked eye
Glassy in appearance
interlocking crystals
interlocking crystals (foliation) -banding
SEDIMENTARY ROCKS
IGNEOUS ROCKS
METAMORPHIC ROCKS
Texture:- Grain size (fine, medium, coarse), sorting and roundness.
are classified primarily on the basis of--
are classified primarily by--
Composition:- based on maturity, one dominant mineral MATURE, range of minerals IMMATURE. TEXTURE
Mineral content. •
Texture. Fine grained (cannot see crystals), medium (see crystals with aid of hand lens), and coarse grained (crystals visible with the naked eye).
Colour (or mineral content). Light coloured minerals (FELSIC) dark coloured minerals (MAFIC)
Web link to Rock Types
Fabric imparted by the agents of metamorphism. They are readily divided into two descriptive groups known as-Foliated. Consist of alignment of minerals often see as banding. (Pressure and heat) Nonfoliated. Crystalline nature, with no banding (heat alone eg marble)
Geology and Soil Mechanics
ROCK TYPES
Geology and Soil Mechanics
Igneous The groups forming the subdivisions from which all igneous rocks are classified are-• •
Intrusive igneous rocks (cooled from magma beneath the earth's surface). Extrusive igneous rocks (cooled from magma on the earth's surface).
Igneous rocks are classified primarily on the basis of-• •
Texture. Colour (or mineral content).
The common igneous rocks are-• • • • • •
Granite. Felsite. Gabbro and diorite. Basalt. Obsidian. Pumice.
Geology and Soil Mechanics Sedimentary Sedimentary rocks, also called stratified rocks, are composed of • • •
chemical precipitates, biological accumulations, or clastic particles.
Loose sediments are converted to rock by several processes collectively known as lithification. These are-• • •
Compaction. Cementation. Recrystallization.
Sedimentary rocks are classified primarily by-• •
Grain size. Composition.
Some typical sedimentary rocks are-• • • • • • •
Conglomerate and breccia. Sandstone. Shale. Tuff. Limestone. Dolomite. Chert.
Geology and Soil Mechanics Metamorphic The alteration of existing rocks to metamorphic rocks may involve the formation within the rock of new structures, textures, and minerals. The major agents in metamorphism are-• • •
Temperature. Pressure. Chemically active fluids and gases.
Metamorphic rocks are classified primarily by-• •
Mineral content. Fabric imparted by the agents of metamorphism.
They are readily divided into two descriptive groups known as-• •
Foliated. Nonfoliated.
The common foliated or banded metamorphic rocks include-• • •
Slate. Schist. Gneiss.
The common nonfoliated metamorphic rocks include-• •
Quartzite. Marble.
Geology and Soil Mechanics
Geology and Soil Mechanics
Activity (click on the link below and follow instructions) Rock Identification • •
Work through the identification process, then identification test. Fill in the table below, print off and include in your portfolio.
Sample Number
Test 1
Test 2
Test 3
Rock Name