| Terms |
Definitions |
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aphanitic
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fine grained
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microseism
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a very small seismic tremor
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breccia
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rock composed of coarse-grained, angular fragments of broken rocks that have been cemented together and lithified
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komatiite
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a typical ultramafic extrusive rock that is mostly olivine and pyroxene, with lesser feldspar
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metasomatism
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the process by which hot-water solutions carrying ions from an outside source move through a rock mass via fractures or pore space
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dike
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an intrusive rock that generally occupies a discordant, or cross-cutting, crack or fracture that crosses the trend of layering in the country rock
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bedding
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the pattern (usually horizontal) of layering in which sediments are deposited
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cirque
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a steep-sided, cirular hollow carved in the top of a mountain from an alpine glacier
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Gondwanaland
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a paleocontinent that consisted of what is now Africa, India, S. America, Australia, and Antarctica
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mafic rock
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an igneous rock containing approximately 50& silica and relatively high percentages of iron, magnesium, and calcium
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A horizon
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the uppermost soil horizon; characterized by the downward movement of water
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Geology
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Science that pursues an understanding of the planet Earth
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differential stress
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stress usually caused by tectonic forces applied to a body of rock from different, but not opposite, directions, stretching the rock mass into an elongate shape
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continent-continent convergence
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the result when two continents collide
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loam
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soil that contains about equal amounts of sand, silt, and clay, as well as abundant organic matter
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distributary
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a small, shifting channel that spreads out across a delta from the main river channel and disperses the sediment load
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lithification
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the hardening of sediment into a rock
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creep
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a mass-wasting event slow enough that it cannot be detected as it is occuring
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foliation
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the alignment of parallel layers or bands of mineral grains in a rock subjectes to prolonged defferential stress and/or shearing
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folded mountain
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a mountain created by intense compressional forces that fold, fault, and metamorphose the rocks, a process that resulted in many of the world's biggest mountain belts
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geothermal energy
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the energy produced when exceptionally hot water underground is tapped by wells and used to generate electricity
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geothermal gradient
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the rate at which temperature increases with depth
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hardness
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a quality of minerals determined by teh Mohs hardness scale
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lahar
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a mudflow originating on a volcanic slope
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end moraine
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an extensive and typically crascent shaped pile of till built up at the front ot a glacier
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ductile
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of a rock, flowing plastically in response to stress
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herringbone cross-bedding
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a distinctive pattern of alternating cross-bedding directions that is reflective of a rhythmic, high-energy environment, such as a tidal zone
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alpine glaciation
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glaciation usually restricted to deep balleys in high mountainous terrain.
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metamorphic rock
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a rock created by solid-state transformation of a rock mass into a rock of generally the same chemistry but with different textures and minerals
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barrier reef
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an elongate reef that develops offshore parallel to a coastline and is separated from the coastline by a deep lagoon
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bedding planes
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demarcations of different layers of sediment
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accretionary wedge
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an accumulation of marine sediment, derived from the subducting plate, that builds up at the edge of a subdiction zone.
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cementation
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the step in lithification in which minerals fill some or all of the pore space and adhere to the sediment fragments, thus producing a sedimentary rock
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cinder cone
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a feature composed of pyroclastic material (not lavas) ejected from a volcanic vent
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Sedimentary
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Rock type formed when sediments are lithified
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horn
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a sharply defined peak that has formed from erosional processes along the rim of a cirque
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bajada
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the joining of alluvial fans at the front of a mountain range in a rolling surface of sediment and gravel
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atoll
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a circular reef in deep water that shelters a lagoon; the result of reef development around the flank of a volcano that has since subsided but to which the corals are still anchored
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laccolith
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an intrusive feature similar to a sill but formed from a more viscous magma that creates a lens-shaped mass between sedimentary layers, arching the overlying strata upward
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geostatic pressure
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pressure that is equally applied to all sides of a deeply bured mass of rock
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joint set
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a series of roughly parallel joints that occur in one direction
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aquitard
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a formation such as shale, clay or unfractured igneous rocks that slows water flow
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meteoric water
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water that is derived from the atmosphere as rain or snow and that moves down i8nto the bedrock from the earth's surface
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assimilation
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the process by which pieces of the country rock melt and mix within a body of magma
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crust
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the outermost zone of the earth, its exterior layer
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convection currents
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currents within a material that are driven mostly by changing temperature gradients
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cleavage
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the ability of a mineral to break along preferred directions, usually along the faces of layered crystals
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chemical sedimentary rock
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a sedimentary rock resulting from biological or chemical prcesses, generally underwater, that crystallizes minerals that accumulate on the sea floor
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longshore current
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a strong current resulting from water bing pushed parallel to the shore by repeated wave action; primary transporter of sand in the shoreline environment
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longshore drift
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the movement of sediment parallel to the shore by wave action
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continental rise
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a very low-angle ridge of sediment that forms between the lower part of the continental slope and the abyssal plain
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drawdown
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a local lowering of the water table around a well
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beach drift
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the zig-zag pattern by which sediment is moved across a beach face by breaking waves
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lava
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magma that is extruded at the earth's surface, as from a volcano
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mantle
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the middle zone o fthe earth, between the core and the crust
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differentiation
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the process by which a magma forms different minerals according to changes in temperature and pressure
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Igneous
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Rock type formed when magma or lava solidifies
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ice sheet
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a glacier that covers a broad expanse of land and is not restricted by a channel
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Missippi Valley-type deposit
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a concentration of lead and zinc thought to be deposited in porous limestones and sandstones by low-temperature water that was driven out of deeper sediments by compaction
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intrusive igneous rock
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igneous rock taht formed from magmas that moved upward into craks and voids deep in the crust and that never reached the surface
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Mohorovicic discontinuity
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(the Moho) the first major boundary of the earth's interior; separates the crust from the underlying mantle
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magnetic anomaly
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an area of magnetism that is either higher or lower than the average magnetic field for that region
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magnetic pole
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a locality at which magnetc lines of force converge to create the strongest point in the magnetic field
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magmatic deposit
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of metallic ore, the result when the minerals settle to the bottom of an intrusive body and form thin, high-grade layers
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coastal straightening
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the process of the headlands being cut back and the flanking beaches being widened
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detachment fault
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a low-angle fault above which is often a series of thrust faults and below which is undeformed bedrock
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desert
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an area that receives less that 25 cm (10 inches) of precipitation annually
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ablation
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the loss of ice and snow from a glacier, generally through melting or evaporation.
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barrier island
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a large, elongate mass of sand that parallels a coast and forms an island
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Benioff zone
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a zone that slopes downward from an oceanic trench and underneath the overlying crustal plate at 30 to 60 degrees; an area of earthquake origination
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desert pavement
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a large surface of the desert floor that is covered by pebbles and stones that resemble rounded paving stones; caused by deflation or temperature changes
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fossil assemblage
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a group of different kinds of fossils that coexisted; more useful than single types of fossils in determining the age of a formation
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graben
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a feature formed when a block that is bounded by normal faults slips downward, usually because of a tensional force, creating a valleylike depression
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graded stream
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a stream that has smoothed out its longitudinal profile to resemble a smooth, concave-upward curve
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hot springs deposit
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a disseminated metal deposit formed in response to hot spring activity at the surface of the earth
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headward erosion
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erosion that results when a valley is extended upward above its original source by gullying, mass wasting, and sheet erosion
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erratic
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a boulder that has been deposited by a glacier and is not derived from the local bedrock
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exotic terrane
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a terrane that did not form naturally through accretion and has likely collided with the continental margin
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law of original horizontality
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a law that states that most sedimentary rocks formed as nearly horizontal layers
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law of superpositition
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a law that states that in an undisturbed sequence of sedimentary rocks or lava flows, the overlying rock is younger than the underlying rock
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hot spring
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a spring with water 6 to 9 degrees centigrade (11 to 16 degrees F) warmer than the mean annual air temperature for the locality where it occurs
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heat flow
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of the earth in general, the amount of heat from the earth's interior that is lost at the surface
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anticline
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a fold that is arched upward to form a ridge
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fault block mountain
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a mountain that is bordered on both sides by steeply dipping faults, such as a horst
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fault plane
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a plane of fracture in a rock along which movement has occured
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fumerole
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a vent in or near a volcano from which steam and other gases escape from molten rock below
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law of faunal succession
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a law that states that fossil species succeed one another in undisturbed rocks in a definite and recognizable order around the world
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bituminous coal
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a common form of coal that is soft and black
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