identify a rock classifying rocks. what characteristics are used to identify rocks? when studying a...
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Identify a Rock
Classifying Rocks
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What characteristics are used to identify rocks?
• When studying a rock sample, geologists observe the rock’s– Color– Texture– Mineral composition
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Texture helps geologists classify rocks. Looking at the rocks below, describe the characteristics of a rock that help you define what a rock’s “grain” is.
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Texture: Grain Size
• Texture is described with the terms based on:
• Grain size– Fine-grained– Coarse-grained
• Grain shape– Smooth – Jagged
• Grain pattern– banded– nonbanded
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What are the three major groups of rocks?• Igneous rock
– Forms from the cooling of molten rock – either magma below the surface or lava at the surface
• Sedimentary rock– Forms when particles of other rocks or the
remains of plants and animals are pressed and cemented together
– Forms below the surface
• Metamorphic rock– Forms when an existing rock is changed by
heat, pressure, or chemical reactions– Most metamorphic rock forms deep
underground
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What tests do geologists use to identify minerals in rocks?• Scratch Test (Mohs)• Acid Test--Use acid to determine
whether the rock contains the mineral calcite
• Magnet test
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Scratch Test: The harder rock/mineral/material will generally scratch the softer rock/mineral/material
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Acid Test: A rock/mineral with calcium or other reactive substance will bubble when hydrochloric acid is placed on it: Limestone, Calcite, and some Sandstones may do this.
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Magnet Test: A rock that is high in iron content may be magnetic: Magnetite is a good example.
Many meteorites are also magnetic!
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ID Key:Many Geologists use an ID key to determine they type and common name of a rock.
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Name: Type: Ig/Sed/Met
Color Texture Minerals Present
Scratch Test: Mohs Hardness
Acid Test:
Granite Igneous White with black specks
Medium (smooth or rough)
Quartz, mica, feldspar
7-scratches steel
N/A
Example of a Rocks ID Chart: