Geology is....

What is Geology

• The scientific study of the origin, history, and structure of the earth.
• The structure of a specific region of the earth's crust.
• A book on geology.
• The scientific study of the origin, history, and structure of the solid matter of a celestial body.

Geology is the study of the Earth, and in particular the history, the structure, the evolution of life, and the processes that have molded the Earth and its inhabitants. The coming of the space age has also extended the field to include the solid planets of the solar system. Although often attracted to the study of geology by an aesthetic appreciation and enjoyment of the earth, geologists commonly approach their studies from an interest either in the academic or the applied aspects of the science.

1. The academic aspects include the study of the history of life, the Earth, and the planets, and of the processes that drive the historical evolution.
The study of historical evolution through "deep time" is what fundamentally distinguishes geology from most of the other physical sciences. The study of the processes that drive this evolution can involve the application of any of the physical or life sciences to understanding the Earth. In this sense, geology is truly an interdisciplinary science.

The applied aspects of the science generally involve the interaction between humans and the earth. Applied studies include the study of mineral resources including oil and water; identification and mitigation of Earth hazards such as earthquakes, landslides, and volcanic eruptions; identification and mitigation of polluted ground water; and land use planning.

Strike and dip

Strike and dip refer to the orientation or attitude of a geologic feature. The strike of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map this is represented with a short straight line segment oriented parallel to the compass direction of the strike. Strike can be given as either a quadrant compass bearing (N25°E for example) in terms of east or west of north or south, a single three digit number representing the azimuth, where the lower number is usually given (where the example of N25°E would simply be 025, and the other value of 335 is discarded), or the azimuth number followed by the degree sign (example of N25°E would be 25° or 335°). The dip gives the angle below the horizontal of a tilted bed or feature, and is given by the number (0°-90°) as well as a letter (N,S,E,W) with rough direction in which the bed is dipping. One technique is to always take the strike so the dip is 90° to the right of the strike, in which case the redundant letter following the dip angle is omitted. The map symbol is a short line attached and at right angles to the strike symbol pointing in the direction which the planer surface is dipping down. The angle of dip is generally included on a geologic map without the degree sign. Beds that are dipping vertically are shown with the dip symbol on both sides of the strike, and beds that are flat are shown like the vertical beds, but with a circle around them. Both vertical and flat beds do not have a number written with them.

Strike and dip 2

Stratum compass to measure strike and dip direction in one step

Strike and dip refer to the orientation or attitude of a geologic feature. The strike of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane.
On a geologic map this is represented with a short straight line segment oriented parallel to the compass direction of the strike. Strike can be given as either a quadrant compass bearing (N25°E for example) in terms of east or west of north or south, a single three digit number representing the azimuth, where the lower number is usually given (where the example of N25°E would simply be 025, and the other value of 335 is discarded), or the azimuth number followed by the degree sign (example of N25°E would be 25° or 335°). The dip gives the angle below the horizontal of a tilted bed or feature, and is given by the number (0°-90°) as well as a letter (N,S,E,W) with rough direction in which the bed is dipping. One technique is to always take the strike so the dip is 90° to the right of the strike, in which case the redundant letter following the dip angle is omitted. The map symbol is a short line attached and at right angles to the strike symbol pointing in the direction which the planer surface is dipping down. The angle of dip is generally included on a geologic map without the degree sign. Beds that are dipping vertically are shown with the dip symbol on both sides of the strike, and beds that are flat are shown like the vertical beds, but with a circle around them. Both vertical and flat beds do not have a number written with them.

Dike

Magmatic dikes

A small dike on the
Baranof Cross-Island Trail, Alaska

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across

• planar wall rock structures, such as bedding or foliation

• massive rock formations, like igneous/magmatic intrusions and salt diapirs.

Dikes can therefore be either intrusive or sedimentary in origin.
An intrusive dike is an igneous body with a very high aspect ratio, which means that its thickness is usually much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters and the lateral dimensions can extend over many kilometers. A dike is an intrusion into an opening cross-cutting fissure, shouldering aside other pre-existing layers or bodies of rock; this implies that a dike is always younger than the rocks that contain it.
Dikes are usually high angle to near vertical in orientation, but subsequent tectonic deformation may rotate the sequence of strata through which the dike propagates so that the latter becomes horizontal. Near horizontal or conformable intrusions along bedding planes between strata are called intrusive sills.
Sometimes dikes appear as swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event. The world's largest dike swarm is the Mackenzie dike swarm in the Northwest Territories, Canada.

Location : Near Randenigala reservoir

The rocks of this area belong to the highland complex with inter banded metamorphosed sediment and charnockitic gneiss but numerous pegmatite dike are found in Vijayan Complex.

The pegmatite is very coarse grained and formed veins due to the slow cooling and evaporation of the fluids.

It has waxy luster.

Many joints but no clear foliation planes.
No mineralization is observed.

It is an igneous plutonic rock that has intruded in to the country rock.

Large Dike

Location : Near Randenigala reservoir
GPS readings : 071058N
845439E

Major rock : Gneiss

Mineralogy : Allanite, Biotite, Orthoclase (K-feldspar),
Plagioclase ( Na, Ca feldspar), hornblende,
mica

Dikes in the Black Canyon of the
Gunnison National Park, Colorado, USA

Shiprock, New Mexico a volcanic neck in the distance, with radiating dike on its south side.

Sedimentary dikes

Sedimentary dikes or clastic dikes are vertical bodies of sedimentary rock that cut off other rock layers. They can form in two ways:
• When a shallow unconsolidated sediment is composed of alternating coarse grained and impermeable clay layers the fluid pressure inside the coarser layers may reach a critical value due to lithostatic overburden. Driven by the fluid pressure the sediment breaks through overlying layers and forms a dike.
• When a soil is under permafrost conditions the pore water is totally frozen. When cracks are formed in such rocks, they may fill up with sediments that fall in from above. The result is a vertical body of sediment that cuts through horizontal layers: a dike.
• In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.
• The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, and petrology is an essential component of geology.

Rock classification

The rocky side of a mountain creek near Orosí, Costa Rica.


Rocks are classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them. These indicators separate rocks into igneous, sedimentary and metamorphic. They are further classified according to particle size. The transformation of one rock type to another is described by the geological model called the rock cycle.

Sample of igneous gabbro

Igneous rocks are formed when molten magma cools and are divided into two main categories: plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth's crust (example granite), while volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta (examples pumice and basalt) .

Rock cycle

The Rock Cycle

‘Rocks are neither created or destroyed, but are redistributed and transformed from one rock type to another’

• Rocks are divided into
families based on how they
are formed • Igneous • Sedimentary • Metamorphic

Igneous rocks are formed when magma or lava, which are liquid, cool and
harden to become rocks.

Sedimentary rocks are made of small pieces of rocks that settle in lakes and seas. The small pieces of rock settle to the bottom in layers and after a long period of time, harden into new rocks.

Metamorphic rocks are rocks
that have been changed by heat, by pressure, or by both.

Geological Instruments

Several instruments were used in the exploration event of the group.
Primary Instrument
# Geological hammer
# Compass with clinometers (Brunton)
# GPS receiver
# Pocket lens
# Hydrochloric acid (HCl)
# Field note book