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# Geology Cheatsheet

## Plate Tectonics

### Plate Boundaries

	
Divergent boundary: where two plates move away from each other
	
Convergent boundary: where two plates move towards each other

  * Subduction zone: where an oceanic plate is forced beneath a continental plate
  * Collision zone: where two continental plates collide

	
Transform boundary: where two plates slide past each other


### Volcanoes

	
Shield volcano: broad, gently sloping, with effusive eruptions
	
Cinder cone volcano: steep, conical, with explosive eruptions
	
Stratovolcano (composite volcano): large, steep-sided, with alternating layers of lava and ash


### Earthquakes

	
Focus: the point beneath the Earth's surface where the earthquake starts
	
Epicenter: the point on the Earth's surface directly above the focus
	
Seismic waves: the waves of energy that travel through the Earth


## Rocks and Minerals

### Rock Types

	
Igneous rock: formed from cooling and solidification of magma or lava
	
Sedimentary rock: formed from the accumulation and lithification of sediment
	
Metamorphic rock: formed from the alteration of pre-existing rock under high temperature and/or pressure


### Mineral Properties

	
Color: the color of the mineral
	
Luster: the way the mineral reflects light
	
Hardness: the resistance of the mineral to scratching
	
Cleavage: the way the mineral breaks along planes of weakness
	
Fracture: the way the mineral breaks along curved or irregular surfaces


## Geologic Time Scale

	
Eon: the largest division of time, based on the abundance of fossils

  * Phanerozoic eon: the most recent eon, characterized by the proliferation of complex life forms

	
Era: a subdivision of an eon, based on significant events in Earth's history

  * Mesozoic era: the era of the dinosaurs

	
Period: a subdivision of an era, based on distinctive rock layers

  * Jurassic period: the period of the dinosaurs

	
Epoch: a subdivision of a period, based on smaller-scale changes in Earth's history

  * Holocene epoch: the current epoch, characterized by the rise of human civilization

## Resources

	
[Geology.com](https://geology.com/)
	
[USGS](https://www.usgs.gov/)
	
[Geological Society of America](https://www.geosociety.org/)