# 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/)