Ch.11.rocks and soil (part 2)
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Minerals are naturally occurring substances formed from elements in the Earth. Rocks are composed of minerals stuck together, while ores contain high quantities of metal compounds and are mined. Soil is formed through the weathering and breakdown of rocks into particles, and provides nutrients and anchoring for plant growth. It has distinct layers and properties depending on its composition of materials like sand, silt, clay and humus that influence texture, drainage and suitability for agriculture. Loam soil with a balanced mixture of components is most favorable for cultivation.
Ch.11.rocks and soil (part 2)
- 2. 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
- 3. - Gold, silver and copper are examples of minerals found on their own. - Most other minerals are compounds. Gold Silver Copper
- 4. - 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.
- 5. - Each mineral can be recognised by: a) Shape b) Colour c) Luster d) Hardness e) Streak colour (when rubbed against a white rough porcelain surface)
- 6. - Some rare minerals have attractive properties (shiny surface, pleasing colour and sparkle) - These minerals are called gemstones. - Example: Opal, diamond and beryl Opal Diamond Beryl
- 7. 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.
- 8. 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.
- 9. 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.
- 10. Types of weathering Physical weathering Chemical weathering • CHANGES IN TEMPERATURE • EFFECT OF ICE • ABRASION • EFFECT OF PLANTS • RAIN WATER • HOT AND WET WEATHER CONDITIONS
- 11. PHYSICAL WEATHERING CHANGES 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.
- 12. 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.
- 13. CHEMICAL WEATHERING RAIN 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.
- 14. 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.
- 15. SOIL IS A MIXTURE OF MANY THINGS. Water Air Tiny pieces of rock Humu s
- 16. PART OF SOIL THAT IS MADE UP OF PARTS OF HUMUS
- 17. TYPES OF SOIL - Soil can have different colors. - Soil can have different sizes of rocks (grains)
- 18. Clay soilSilt soilSand soil Types of soil Properties Size of particles StickySmoothGritty (coarse) Texture (Feel when wet) Not much air space Some air spaceLots of air spaceAir space Does not pass (Stays wet) Stays a while Passes fast (Dry fast) Water
- 20. - 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.