aa — A type of lava flow characterized by its lumpiness and viscosity. When it cools, the rock it forms may be sharp.
absolute dating — A technique that geologists use to assign specific dates to rock formations and geologic events.
ash — A substance that shoots out of a volcano that's two millimeters or smaller in diameter.
cleavage — The way crystalline minerals split or break along an even plane (planar surfaces).
cross cutting relationships — A fundamental principle of geology, which states that rocks that cut through other rocks are younger than the rocks being cut.
faunal & floral
succession — A fundamental principle of geology, which states that unless disturbed, the oldest fossils in a rock bed should be at the bottom.
fracture — In rocks, a break along an uneven (non-planar) surface.
geologists — Cool guys and gals who study rocks and the Earth.
hardness — A rock or mineral's ability to resist abrasion.
igneous rock — A rock that forms when molten rock cools down and crystallizes.
lateral continuity — A fundamental principle of geology, which states that sediments are deposited initially in a layer that extends horizontally in all directions.
lava — Hot, melted rocks that reach the Earth's surface.
lithification — The process that turns sediment into sedimentary rock.
luster — The way that minerals reflect light. There are two types of luster: metallic and nonmetallic.
magma — Hot, melted rock that's below the Earth's surface.
Mohs hardness scale — A scale that measures and compares the hardness of minerals.
original horizontality — A fundamental principle of geology, which states that sediments settle and accumulate horizontally on the sea floor.
pahoehoe — Congealed surface lava is dragged along over hot-moving lava. The congealed part rolls over the hot part, forming folds that look like ropes.
pumice — A form of volcanic glass that's filled with holes. These holes form when gases escape from lava.
relative dating — A technique geologists use to assign a sequential order to the age of rocks and geologic events. The oldest comes first, and subsequent events follow on a relative dating line.
sedimentary
rocks — Rocks formed from things like little pieces of gravel, sand, silt, and clay, as well as the remains of animals and plants.
superposition —
A fundamental principle of geology, which states that if a rock bed hasn't been disturbed since it was formed, it is younger than the layer of rock below it.
tuff — A type of igneous rock formed by the consolidation of ash.
uniformitarianism
— A fundamental principle of geology, which states that we can understand geologic events of the past by looking at geologic events of the present. According to uniformitarianism, a volcano eruption that happens today is pretty much like a volcano eruption that happened million years ago.
