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ROCKS AND SOILCHAPTER 11 (PART 2)
CHEMISTRY
MINERALS- Is a substance that has formed from one
or more elements in the earth.- Rocks are formed from different
minerals stuck together.- Example: Granite rock (mixture of feldspar, quartz and mica)
r r
- Gold, silver and copper are examples of minerals found on their own.
- Most other minerals are compounds.
Gold
Silver
Copper
- The atoms of elements in a mineral usually join together to form a crystal structure.
- Example: Silicon and oxygen form a crystal substance called quartz.
- Each mineral can be recognised by:a) Shapeb) Colourc) Lusterd) Hardnesse) Streak colour (when rubbed against a white
rough porcelain surface)
- Some rare minerals have attractive properties (shiny surface, pleasing colour and sparkle)
- These minerals are called gemstones.- Example: Opal, diamond and berylOpal Diamond
Beryl
ORES• DURING THE FORMATION OF SOME ROCKS
(SEDIMENTARY ROCKS) METAL ELEMENTS GATHER IN LARGE QUANTITIES.
• ROCKS THAT POSSESS LARGE QUANTITIES OF METAL COMPOUNDS ARE CALLED ORES.
• BAUXITE IS AN ORE RICH IN ALUMINIUM.
• HAEMATITE IS AN ORE RICH IN IRON.
• ORES ARE MINED AND THEN PROCESSED, USUALLY USING HEAT.
SOIL• SOIL IS USUALLY COVERED WITH PLANTS THAT
GROW IN IT.
• SOIL HELPS PLANTS TO SET DOWN THEIR ROOTS AND HOLD THEIR POSITION IN A HABITAT.
• SOIL ALSO STORES WATER AND MINERALS FOR PLANTS TO USE AS THEY GROW.
• SUCCESSFUL FARMING DEPENDS ON SOIL SO OVER THE YEARS SCIENTIST HAVE STUDIED SOIL.
HOW SOIL FORMS.- The main part of soil is made from small
particles or fragments of rock.- The process by which rock breaks down
to form fragments is called weathering.
Types of weathering
Physical weathering
Chemical weathering
• CHANGES IN TEMPERATURE
• EFFECT OF ICE
• ABRASION • EFFECT OF PLANTS
• RAIN WATER
• HOT AND WET WEATHER CONDITIONS
PHYSICAL WEATHERINGCHANGES IN TEMPERATURE
• WHEN ROCKS HEAT UP THE MINERALS EXPAND BY DIFFERENT AMOUNTS, SO THEY PUSH ON EACH OTHER.
• WHEN THEY COOL DOWN THEY CONTRACT AND SPACES DEVELOP BETWEEN THEM.
• AFTER BEING HEATED AND COOLED MANY TIMES THEY BECOME LOOSE AND FALL AWAY.
• IN THE SAHARA DESERT TEMP. DURING THE DAY IS ABOVE 40 ⁰C AND DURING NIGHT IT IS BELOW -7 ⁰C SO THE ROCKS CRUMBLE.
EFFECT OF ICE• WHEN IT RAINS ON POROUS ROCK LIKE SANDSTONE
THE WATER CAN STAY IN THE ROCK FOR SOME TIME.
• WHEN THE WATER IN THE ROCK FREEZES IT EXPANDS.
• ICE PUSHES ON THE SIDES OF THE PORES AND MAKES THE ROCK CRUMBLE.
• WATER MAY COLLECT IN CRACKS AND FREEZE, PUSHING AGAINST THE SIDES AND MAKING ROCKS BREAK.
ABRASION• OCCURS WHEN PIECES OF ROCK RUB TOGETHER.
• EXAMPLES: WHEN PEBBLES ARE CARRIED IN A FAST FLOWING RIVER.
• GLACIERS MOVING SLOWLY DOWN MOUNTAINS RUB ON THE ROCKS IN THE VALLEY FLOOR AND SIDES AND WEAR THEM DOWN
• SAND GRAINS BLOWN IN THE WIND (SANDSTORM) RUB ON ROCK SURFACES AND WEAR THEM DOWN.
• HIGH TIDE THROWS PEBBLES ON BEACHES
EFFECT OF PLANTS• IF THE SEED OF A TREE OR BUSH SETTLES IN A
CRACK AND GERMINATES THE ROOT CAN GROW IN THE SOIL (SETTLED INSIDE THE CRACK).
• TREES AND BUSHES HAVE STRONG, WOODY ROOTS THAT GROW LARGER EVERY YEAR, SO THEY PUSH ON ITS SIDES AND BREAK UP THE ROCK.
CHEMICAL WEATHERINGRAIN WATER
• ACID IN RAINWATER FALLING ON ROCKS SUCH AS GRANITE CAN BREAK IT UP INTO SMALLER PIECES.
HOT AND WET WEATHER CONDITION
• HOT, WET WEATHER CONDITIONS SPEED UP CHEMICAL REACTIONS MORE QUICKLY THAN DRY, COLD CLIMATES
• WHEN TINY ROCKS AND SAND CARRIED BY WIND AND WATER SETTLE DOWN IT FORMS SOIL.
LAYERS OF SOIL
Topsoil
Subsoil
Bedrock
Has lots of Humus. Many small animals live in it.
Does not have lots of Humus, but it has small pieces of rock
It has no Humus. Made up of solid rock.
SOIL IS A MIXTURE OF MANY THINGS.
Water Air
Tiny pieces of rock
Humus
PART OF SOIL THAT IS MADE UP
OF PARTS OF DEAD PLANTS AND ANIMALS.
HUMUS
TYPES OF SOIL -Soil can have
different colors. -Soil can have
different sizes of rocks (grains)
Clay soil Silt soil Sand soil
Types of soil
Properties
Size of particles
Sticky Smooth Gritty (coarse)Texture
(Feel when wet)
Not much air space Some air space Lots of air space Air space
Does not pass(Stays wet) Stays a while
Passes fast(Dry fast) Water
- Loam is a type of soil made of 40% sand, 40% silt and 20% clay.- It contains large amount of humus.- It is the most suitable for cultivation.