Download mks rocks and minerals

ROCKS AND MINERALS
MARKING SCHEME
1996 Q 5
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- Sandstone
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New Minerals are formed
Minerals recrystallize further
Rock particles become compacted
The physical appearance of the rock changes
Metamorphism without any details
- Clay stone, siltstone -shale
-Mudstone
(Any 2x 1 = 2 marks)
1997 Q 9
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Likmonite – chert
Travertine / tufa
Dolomite
Rock salt
Gypsum
Haemitite
Trona
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Temperature between 20 – 29 oC
Warm water
Salty water
Shallow water
Clear water / silt free / mud free
Well – oxygenated water
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Tiny marine organism called coral polyps live in colonies in the sea.
Polyps extract calcium form the sea water to make their shells.
The spaces between the dead coral polyps are cemented by calcareous
algae.
Some rocks are exploited to provide building and construction materials.\
This promotes the industry.
Some rocks formation e.g. granite are tourist attractions. This earns the
country some foreign exchange.
Rocks have contributed to the development of cement industry through the
provision of lime – stone as raw materials.
Through weathering, rocks provide soils which are used for agricultural
production.
Some rocks have valuable mineral ores which are exploited and sold to
generate revenue
Some rocks are curved for which are sold to generate revenue
Some rocks such as rock salt are sources of food.
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2000 Q 7a
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Plutonic rocks
Form from magma
Formed deep inside the crust/intrusive/ Extrusive
Cools slowly
Forms large cry/course grained
Coarse textured
Volcanic rocks
-Form from lava
-Formed in surface
-Cools rapidly
-Forms small crystals
-Fine textured
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2001 7a-c
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A rock is a substance made up of a mineral / combination of mineral
particle cemented together and forms the solid part of the earth’s crust.
Mechanically Formed
These rocks are formed when eroded rock materials are transported by
agents of erosion and deposited in layers either on land or in the sea
Organically formed
These rocks are formed when remains of previously existing plants or
animals organizations are accumulated over a period of time forming
layers
Chemically formed
These are formed when rocks are precipitated or when solutions of salt
evaporate and particles accumulate in layers.
When the weight of the overlying rock layers creates pressure on the
lower layers it leads to change in structure/ grain alignment of the rocks.
This process is known as dynamic
During volcanic eruptions, hot magma/ liquids may intrude into a
sedimentary rock. The rock grains will re-crystallize due to heat to form
new minerals. This process is known as thermal/ contact metamorphisms
In the mountain building process, sedimentary rocks are compressed and
due to this pressure heat is generated. This heat modifies the structure of the
original rocks. This process is known as thermal – dynamic metamorphism
(iv) Plutonic rocks
Granite
Syenithe/ Gabbro
Diorite/ Poridatite
Hypabyssal Rocks
Dolorite/ Perplymite/ Porphyry
Lamprophyre, biamphyre
Volcanic rocks
Andesite
Pumice
- Tephrite
Trachite
Scoria
- Ryolite
Phonolite
Basalt
- Obsidian
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2003 Q 5
a)
(i)
Granite
- Gneiss
(ii)
Clay
- slate
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The coastal plain is a lowland, which has facilitated deposition of sediments
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The shallow continental shelf has conclusive environment for the formation
of coral rocks
2007 Q 7a-c a)
(i) colour
(2 marks)
 All minerals have their specific characteristics colour. Some change colour
when exposed e.g gold is yellow, copper oxides are blue or green e.t.c
ii)
Cleavage
(2 marks)
 Minerals have distinct cleavages. They have patterns in which they split or
divide e.g mica split into thin layers. Plant and glass has distinctive facture.
iii)
Hardness
(2 marks)
 Minerals differ in hardness depending on their chemical constituents and mode
of formation. E.g Talc is soft, quartz is moderately hard and diamond is the
hardest.
b) i) -Intrusive/plutonic rocks
-Extrusive/hypabyssal rocks (2x1)
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Shallow water
Well oxygenated
Clear water i.e. silt free
Warm water with temp 200C-290C (any 3x2)
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Valuable source of minerals like gold
Store underground water i.e impermeable rocks
source of income and employment
tourist attraction sites.
provide construction materials.
Making of artifacts e.g soap stones
Breakdodown into fertile soils
(any 4x1)
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Coal, Nitrates, graphite, sulfur, potash.
Asbestors, Sodium, diamond, silicon.
Petroleum.
Fluorspar.
(2 marks)
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Because it is the hardest mineral/it does not break easily.
(1 mark)
2008 Q 3
2009 Q 1
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Plutonic rocks form from magma which cools slowly and solidifies within
cracks and chambers in the earth’s crust while volcanic rocks form from the
lava that cools fast and solidifies onto the surface of the earth
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Sandstone Quartzite \late
Limestone - Marble
Clay
Slate \ Schist
2010 Q 4
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Any naturally formed solid aggregate/a naturally occurring solid material
composed of one of minerals.
Some sedimentary rocks contain fossils.
The rocks have cleavage/are foliated/have planes
The rocks horizontal layers/are stratified.
(any 3 x 1 = 3 marks)
2010 Q 6c PP2)
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High temperatures in arid and semi arid areas cause evaporation of water in
lakes/seas.
This leads to high concentration of mineral salts in the water. Continued
evaporation causes further recrystallization of the salts which may thereafter
be attracted as minerals such as soda ash and common salt/deposition of salts
near the surface.
(2 marks)
Volcanicity
When molten magma intrudes into rock joints minerals contained in the
magma embedded in the joints called veins. Such minerals as tin and Copper
occur in this form/Hop springs/gersey. Fonaliss bring minerals to the earth’s
surface.
(2 marks)
Metamorphism
High pressure and heat cause recrystallization and hardening of certain rocks
causing them to change their nature to ebcome minerals such as diamond.
(2 marks)
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2012 Q7
(a) (i) mineral is an organic substance with a definite chemical composition at/beneath the
surface of the earth
(ii) lustre – minerals differ in their brightness depending on nature of their reflective
surfaces.(smooth surfaces are dull.
Colour – different minerals display different colours. Minerals that have iron/
magnesium have dark colours.
Density-minerals have different weight per unit volume of water.
(b) (i) – basalt
- rhyolite
- pumice
- obsidian
- tuff
- andesite
(ii) mechanically formed sedimentary rocks – rock fragments are transported by
wind/water/ice. they are deposited in layers. Over a long period of time, they are
compacted into a hard rock
Organically formed sedimentary rocks – dissolved minerals are transported in layers.
Over a long period of time, the remains are compacted forming a hard rock.
Chemically formed sedimentary rocks- dissolved minerals are transported into water
bodies.They are then precipitated/evaporated over along period of time. the
precipitates/evaporates are then compacted. To form hard a rock
(c) (i) tourism: some rocks form unique features that attract tourists earning the country
foreign exchange.
(ii) energy: some sedimentary rocks contains fossil fuels which are sources of energy for
domestic/industrial use.
(iii) water: some rocks act as storage for water which can be supplied for
Domestic/industrial/agricultural
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