Fundamentals of Rock Classification: Texture, Composition, and Major Groups
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Fundamentals of Rock Classification: Texture and Composition
Analyzing Rock Samples
When studying a rock sample, geologists observe several key characteristics:
- Mineral Composition: The types and amounts of minerals present.
- Color: Often indicative of mineral content.
- Texture: The look and feel of the rock's surface.
Defining Rock Grains
Most rocks are made up of particles of minerals or other rocks, which geologists call grains.
What is Rock Texture?
Rock texture is the look and feel of the rock’s surface.
Types of Rock Texture
(Note: The specific types of rock texture were not detailed in the original source material.)
The Three Major Rock Groups
Geologists classify rocks into three primary groups:
- Igneous Rock
- Sedimentary Rock
- Metamorphic Rock
Igneous Rocks: Classification and Types
Igneous Rock Classification Criteria
Igneous rocks are classified according to three main characteristics:
- Origin (where they formed)
- Texture (grain size and arrangement)
- Mineral Composition
Extrusive vs. Intrusive Igneous Rocks
- Extrusive Rock
- Igneous rock formed from lava that erupted onto Earth’s surface.
- Intrusive Rock
- Igneous rock that formed when magma hardened beneath Earth’s surface.
Characteristics of Common Igneous Rocks
Granite
Granite is generally a light-colored rock that has high silica content.
Basalt
Basalt is a dark-colored rock that is low in silica.