Introduction to Petrology

• Petrology is the branch of geology focused on the study of rocks and their formation.
• The term "petrology" comes from the Greek words "petros" (rock) and "logos" (study).
• Petrology utilizes mineralogy, microscopic petrography, and chemical analyses to describe rock composition and texture.

Petrology Sub-Disciplines

• Experimental petrology involves laboratory synthesis of rocks.
• Experimental petrology aims to ascertain the physical and chemical conditions of rock formation.
• Petrography is the systematic classification and precise description of rocks.

Types of Rocks

• Igneous rocks form from the solidification of magma or lava.
• Igneous rocks are hard and have no layers.
• Sedimentary rocks form from sediment compaction.
• Sedimentary rocks are crumbly and layered.
• Metamorphic rocks form by the transformation of other rocks.
• Metamorphic rocks are relatively hard and may or may not have layers.

Rocks: Classification and Differences

• Rocks are combinations of minerals formed from an aggregation of one or more minerals and other substances.
• Rocks can be classified as Igneous, Sedimentary, and Metamorphic.
• Differences among rock types include mineral content, compositions, texture, sizes, and colors.

Processes of the Rock Cycle

• The rock cycle includes weathering, erosion, transportation, deposition, compaction, cementation, metamorphism, rock melting and crystallization.

Igneous Petrology

• The word "igneous" comes from the Latin word "ignis," meaning "fire."
• Igneous rocks are primary rocks and the most abundant in the Earth's crust.
• They form at high temperatures and pressures through the solidification of magma or lava.
• Magma is molten rock beneath the Earth's surface.
• Lava is molten rock that has reached the Earth's surface.

Magma vs. Lava

• Lava is molten rock that reaches the Earth's surface through volcanic vents.
• Lava can be found at the bottom of oceans, in mid-ocean ridges, accounting for more than 75% of the Earth's volcanic activity.
• Magma is molten rock stored under the Earth's surface.

Occurrence of Igneous Rocks

• Igneous rocks result from magma's final solidification at the surface or at variable depths within the Earth.
• Igneous rocks can also form from the consolidation of fragmented debris.
• Igneous rocks occur in two ways: extrusive (on the surface) and intrusive (below the surface).

Extrusive/Volcanic Rocks

• Extrusive rocks form when lava solidifies.
• They are formed above ground and can also form from ash.
• Extrusive rocks are semi-crystalline.
• They cool quickly and usually have small grains.

Intrusive/Plutonic Rocks

• "Plutonic" refers to Pluto, the Greek god of the infernal regions, signifying deep-seated origins.
• Intrusive rocks form when magma solidifies.
• They are sturdy and durable.
• Intrusive rocks cool slowly and usually have large grains.

Sedimentary Petrology

• Sedimentary petrology studies the composition and texture of sedimentary rocks.
• Sandstone or limestone consist of sedimentary particles bound together in a matrix of finer material.

Sedimentary Rocks

• Sedimentary rocks are formed when sediment becomes cemented into solid rock.
• They are also known as "stratified rocks".
• These rocks undergo processes of cementation and compaction.
• They are formed on or near the Earth's surface.
• The primary geological processes include erosion, weathering, dissolution, precipitation, and lithification.
• Modes of transportation include glaciers, wind, water, and gravity.

Sedimentary Petrology Transformation and Deposition

• Modes of Sediment Transportation: Glaciers, Wind, Water and Gravity
• Environmental deposition occurs in deep sea floors, beaches, desert dunes, river channels, and lake bottoms.

Sedimentary Petrology: Diagenesis

• Diagenesis is the physical and chemical changes that occur during the conversion of sediment to sedimentary rock.

Sedimentary Petrology: Compaction and Cementing

• Quartz, calcite, iron oxide, clay, glauconite, and feldspar are involved in compaction and cementing.