ROCK IDENTIFICATION LAB
What type of rock is this? Where or how is it formed?
Obsidian
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Mafic (black) Extrusive Igneous Rock
No crystals formed
Glassy
Very quick cooling molten rock (lava)
What type of rock is this? Where or how is it formed?
Basalt
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Mafic Extrusive Igneous Rock
Fine grained (some small crystals)
Formed from dark dense lava
 Pyroxene, plagioclase feldspar
What type of rock is this? Where or how is it formed?
Scoria
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Mafic Extrusive Igneous Rock
No crystals formed
Forms as a frothy crust on the top of a
lava flow or as material ejected from a
volcanic vent and solidifying while
airborne
Many holes formed - gasses released
What type of rock is this? Where or how is it formed?
Pumice
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Felsic Extrusive Igneous Rock
No crystals formed
Quick cooling molten rock (lava)
Many holes formed - gasses released
Floats on water
What type of rock is this? Where or how is it formed?
Granite
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Felsic Intrusive Igneous Rock
Coarse Grained - can see crystals
Contains quartz and feldspar
What type of rock is this? Where or how is it formed?
Shale
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Clastic Sedimentary Rock
Thin, dark gray sheets – easily broken
Formed from mud and clay being
pressed together
What type of rock is this? Where or how is it formed?
Image Source
Sandstone
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Clastic Sedimentary Rock
Light red/dark pink with very small
pieces of sand
Quartz cemented by silica or lime
Most form in shallow seas
What type of rock is this? Where or how is it formed?
Image Source
Coal
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Organic Sedimentary Rock
Black, smooth and lightweight
Formed from layers of plant remains
that are pressed together over time
What type of rock is this? Where or how is it formed?
Image Source
Limestone
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Organic Sedimentary Rock
Calcium Carbonate - calcite
Forms from the accumulation of shell,
coral, and fecal debris in clear, warm,
shallow marine waters
What type of rock is this? Where or how is it formed?
Conglomerate
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Clastic Sedimentary Rock
Red with rounded pebbles cemented
together
Formed near moving water
What type of rock is this? Where or how is it formed?
Quartzite
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Metamorphic Rock
Non-Foliated
Individual quartz grains have
recrystallized but are too small too see
Metamorphism of Sandstone
What type of rock is this? Where or how is it formed?
Marble
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Metamorphic
Non-Foliated
Made of mostly small to medium sized
calcite crystals
Metamorphism of Limestone
What type of rock is this? Where or how is it formed?
Gneiss
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Metamorphic
Foliated – pink and grey alternating
bands
Medium to coarse grained texture
Metamorphism of Granite
What type of rock is this? Where or how is it formed?
Slate
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Metamorphic Rock
Foliated
Breaks into thin “slices”
Metamorphism of Shale
What type of rock is this? Where or how is it formed?
Hornfels
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Metamorphic Rock
Non-foliated
Fine grained crystals
Metamorphism of clays or Shales
Comparisons
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Basalt vs. Slate
 Both
dark colors
 Basalt is igneous and Slate is metamorphic
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Pumice vs. Basalt
 Both
igneous made of quick cooling lava (extrusive)
 Pumice is felsic and Basalt is mafic
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Granite vs. Gneiss
 Both
have course grains/crystals
 Granite is igneous and Gneiss is metamorphic
Comparisons
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Scoria vs. Pumice
 Both
are porous (have air bubbles/holes)
 Scoria is mafic and Pumice is felsic
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Obsidian vs. Coal
 Both
are black, no crystals
 Obsidian is igneous and Coal is sedimentary
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Marble vs. Limestone
 Both
are made of calcite
 Marble is metamorphic and Limestone is sedimentary
Comparisons
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Slate vs. Shale
 Both
thin slices, made of mud and clay, dark color
 Slate is metamorphic (morphed from shale), Shale is
sedimentary
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Hornfels vs. Slate
 Both
metamorphic rocks made from Shale
 Hornfels is not foliated and Slate is foliated
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Sandstone vs. Quartzite
 Both
grainy and made of Quartz
 Sandstone is sedimentary and Quartzite is metamorphic
Comparisons
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Limestone vs. Marble
 Both
are made of calcite
 Limestone is sedimentary and Marble is metamorphic
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Conglomerate vs. Limestone
 Both
sedimentary rocks formed in or near water
 Conglomerate is clastic (made of pebbles cemented
together by moving water) and Limestone is organic
(made of shell coral, fecal debri found in shallow water)
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Gneiss vs. Granite
 Both
contain course grain crystals
 Gneiss is metamorphic and Granite is igneous
Comparisons
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Quartzite vs. Sandstone
 Both
contain the mineral Quartz
 Quartzite is metamorphic (pressure and heat),
Sandstone is sedimentary (cemented together by water
+ sandstone or lime)
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Coal vs. Obsidian
 Both
are black and smooth and contain no crystals
 Coal is sedimentary and Obsidian is igneous
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Shale vs. Slate
 Both
made of mud and clay (Slate is made from Shale)
 Shale is sedimentary and Slate is metamorphic