Geology: Glossary

B

bed

a layer of sediment or sedimentary rock

boulder

a loose rock larger than 256 millimeters (10 inches)

C

cleavage

the shape that occurs when a rock is split cleanly

cobble

loose particles of rock or mineral that are the size of gravel larger than pebbles, but smaller than boulders

conglomerate

sedimentary rock made of rounded pebbles held in together with a matrix

continent

one of seven main land masses on the earth

core

the huge mass in the very center of the Earth made mostly of iron and nickel. It is divided into an outer core and inner core

crust

the solid outermost part of the Earth. The crust is all the land you see and the land on the ocean bottom

crystal

a solid in which the particles are arranged in a pattern to make shapes with flat surfaces

crystal shape

crystals often form regular geometric shapes (cubes, hexagonals, etc.) which can aid in their identification

E

earthquake

sudden release of energy built up in an area on the crust or upper mantle sudden ground motion or vibration of the Earth

element

substances which cannot be broken down into other substances

epicenter

the location on the surface of the earth just above the focus of an earthquake

erosion

the movement of weathered rocks and soil

extrusive rock

volcanic rock which solidifies on the surface of the earth rather than inside of the earth

F

fault

a crack in the earth's crust where earthquakes often occur

focus

the location under the earth's surface where an earthquake occurs

formation

a body of rock with special that allow geologists to map, describe, and name it

fossil

something that has lasted from a living thing that died long ago. They can be body parts, that have turned into stone or animal tracks

G

geologist

a scientist who studies geology

geology

the science of the rocks and minerals that compose the earth, of its structure, and of its history

gravel

all sedimentary particles larger than 2 millimeters is called gravel. Gravel is subdivided into pebbles, cobbles, and boulders

H

hardness

A measure of the ease with which a smooth surface of a mineral can be scratched. See Mohs scale

I

igneous rock

rock formed when molten rock has cooled and solidified

intrusive rock

igneous rock that forms when magma cools below the Earth's surface

L

lava

molten rock that flows out onto the Earth's surface

luster

how light reflects off of a rock or mineral

M

Mohs scale

a scale used to measure the hardness of a mineral

magma

molten rock that is located beneath the Earth's surface

magnetism

the naturally-occurring electrical field in some rocks

mantle

the thick layer of very hot, melted rock between the crust and the core of the Earth

matrix

fine-grained material surrounding larger grains in a sedimentary rock

metamorphic rock

rocks that are changed from sedimentary, igneous or other metamorphic rocks by intense pressure and heat

mineral

a non-living, solid material with particles arranged in a repeating pattern called a crystal. A mineral is usually a combination of 2 or more elements. A mineral cannot be broken down into any other substance

mineralogist

a scientist who studies the identification, properties, and distribution of minerals

molten

melted

P

pebbles

Loose particles of rock or mineral that range in size from 2 - 64 millimeters in diameter. Pebbles are the smallest type of gravel

R

Richter Scale

a measurement scale for identifying the amount of energy released by an earthquake

rock

a combination of 2 or more minerals which have been joined either by heat, temperature, pressure, or chemical changes

rock cycle

the process in which igneous, sedimentary, and metamorphic rocks are changed over time

S

sand

loose particles of rock or mineral that range in size from 0.0625 to 2.0 millimeters in diameter

sediment

material that comes from the weathering of rock or from from fragments of plants and animals that settles to the bottom of rivers, lakes, and seas

sedimentary rock

rock formed from rock types that have weathered, cemented, and/or squeezed together

sedimentation

the process of breaking up rocks into smaller fine pieces that sink to the bottom of rivers, lakes, and seas

seismologist

a scientist who studies the waves created by an earthquake

shale

soft rock formed from layers of mud soil

strata

layers, or bands, in rocks

streak

the color that shows when a mineral is scratched on the surface

T

tectonic plates

huge sections of the earth's crust that float on the mantle

V

vent

An opening in the earth's surface

volcanic

igneous rock that forms when magma cools on the Earth's surface

W

weathering

the breaking of rocks by water, snow, ice, wind, chemicals, gravity or plant roots