Download Chapter 14 Rocks and Minerals

Chapter 14 Rocks and Minerals
14.1 Identifying Earth Materials
Geologist – a scientist who identifies, classifies, and studies rocks.
Minerals – a solid inorganic material occurring in nature. Most are
chemical compounds. (What’s a compound?)
• Quartz is a form of silicon dioxide (SiO2)
• Sulfur often appears in its elemental form
• Copper also.
Rock – a combination of two or more minerals that can occur in many
different proportions.
Examine granitewhite or pink Æ feldspar
glassy crystals Æ quartz
flakes Æ mica
Identifying Minerals
Colour – (Duh!) problem with this is that many minerals appear in
different colours.
Hardness – (Don’t test by biting, okay? Your dentist won’t appreciate
it). We use the Mohs Hardness Scale . We use this by doing a
scratch test…scratch one mineral with another.
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Talc
Gypsum
Calcite
Fluorite
Apatite
Feldspar
Quartz
Topaz
Corundum
Diamond
softest
hardest
Lustre – how a mineral reflects light.
Metallic
Glassy
Oily
Streak – this refers to what colour of a mark is produced when you
scratch a piece of porcelain tile with the mineral.
Magnetism – you can test this with a magnet or a compass.
Unfortunately there are only four minerals (elements in this case!)
that have magnetic properties.
Iron
Nickel
Cobalt
Gadolinium
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Usually, a mineral that has a magnetic property will have iron or
maybe nickel. Cobalt and gadolinium are quite rare.
Fluorescence – the ability to absorb and emit light. Simply, this
means a rock will glow with a different colour when under ultraviolet
light.
Fluorite Æ blue or purple
Calcite Æ red, pink, yellow
Crystals – minerals can be classified according to the shape of their
crystals. Salt, for example, always forms cubes. Large crystals are
generally rare in nature. Small crystals which can be seen under
magnification are very common.
Cleavage and fracture – some rocks will split apart certain ways if
you hit it with a hammer or drop it on the ground.
Slate and shale split in sheets.
Obsidian flakes apart.
Cleavage - when rocks to produce smooth surfaces.
Mica
Galena
Feldspar
Fracture – when rocks break into rough chunks.
Quartz
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Classifying Rocks
There are essentially 3 classes of rocks:
Igneous
Sedimentary
Metamorphic
Thickness of earth’s crust
Beneath oceans – 5 km
Beneath continents – up to 50 km
Igneous
“born of fire” – produced when molten rock (called MAGMA) from
deep in the earth reaches the earth’s crust. From there it has three
choices.
1) Recycle back to the center of the earth.
2) Intrusive – where it forces its way into cracks, but never comes
out of the ground. This is the cause of ‘veins’ of rock.
3) Extrusive - It breaks through the surface as LAVA out of
volcanoes, where it cools.
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Special note: the appearance of igneous rocks depends on many
things, like mineral content and how quickly the lava cooled. If it cools
slow, crystals will form…if cooling is too fast Æ no crystals!
Sedimentary
Means “born of water” – the cementing together of rock pieces of
various sizes. This normally involves a water event such as a flood or
water erosion plus pressure. Rivers often deposit huge amounts of
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silt and other sediments. Overlayering can produce great pressure.
Other minerals can act like glue. These eventually form sediment
‘beds’.
• Mudstone , shale - from fine clay or mud.
• Sandstone – from sand
• Conglomerate – larger chunks
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Metamorphic
Metamorphic means “new body” – where sedimentary or igneous
rocks are put under great temperature and pressure and change into
a new form. A certain ‘start’ rock can turn into different types of
metamorphic rock depending upon the amount of pressure and heat
which it experiences. However, the new rock is usually:
• harder
• more brittle
How are heat and pressure are applied?
1) downward pressure of overlayering (burial) by sedimentary rock
2) upward pressure of magma
3) lateral tectonic pressure at fault lines
4) heat from contact, or near contact with magma
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The Rock Cycle
The rock cycle represents the many pathways that rocks can take
during its “lifetime”. For example a metamorphic rock can be
weathered to sedimentary rock or pressurized to metamorphic or
even recycled to igneous again. See how many pathways you can
suggest for a rock to take…endless, isn’t it?
Chapter Review
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