Identify the different types of minerals and rocks in Rwanda
Locate the major minerals and rocks in Rwanda
Recall the economic importance of rocks and minerals.
1. Unit 4: Rocks and
minerals in
Rwanda
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2. By the end of this unit, you
should be able to:
1.Identify the different types of minerals and rocks
in Rwanda
2.Locate the major minerals and rocks in Rwanda
3.Recall the economic importance of rocks and
minerals.
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3. Types of minerals and rocks in Rwanda
Mineral: is a natural and
inorganic solid with definite
chemical composition and
characteristic physical
properties.
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Rock is a naturally occurring solid
that is made up one or more
minerals.
Examples of minerals
are quartz (Sio₂), iron
(Fe), aluminium (al),
etc.
Examples of
Rocks are slate,
marble, quartzite,
samdstone, etc
4. Brief history of Rwandan rocks and
minerals
In Rwanda the largest parts are made up of Burundian
rocks (1050-980 million years). These are associated
with the folded sediments of Western and Eastern
Provinces.
These are rocks that changed their mineralogical and
chemical compositions due to metamorphism.
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Shist
The specific examples include schist and quartzite that were
exposed forming granite. These rocks occupy the greatest part of
Rwanda
Shist and Quartzite
7. Physical properties of rocks
• Rocks have different colors: black for basalt, red for ironstones,
white for quartzite and gypsum, etc.
• Hardness: the ability of rocks to resist scratching. Some rocks
are hard and others are soft.
• Rocks have different texture: size of their components or crystals.
• Some rocks are permeable (loose, fractured and porous to permit
the absorption of water) and others are impermeable.
• Rocks have different density
• Some rocks are consolidated like granite, quartzite, etc. others
are unconsolidated or loose like sand and gravels
• Luster: light reflected from the surface of a mineral or a rock.
The luster may be metallic or non metallic.
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9. Chemical properties of Rocks
• Chemical composition
• Solubility and insolubility in water
• Oxidation that is the reaction with oxygen
• Carbonation that is the reaction with carbonic acid
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10. Rocks of Rwanda
1. Igneous rocks: These
are rocks that result
from the cooling and
solidification of
magma. Located in the
north western and the
south western regions
of Rwanda.
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11. Types of igneous rocks in Rwanda
1. They are into two types:
1. Extrusive rocks: They formed when lava solidified at
the surface. These extrusive rocks are basalt, obsidian,
ashes and cinders, etc. They are abundant in Northern
Province (Musanze and Burera) and in Western
Province (Nyabihu, Rubavu, Rutsiro, Rusizi and
Nyamasheke districts). They are dark because they
come from basic and fluid lava.
2. Intrusive or plutonic rocks: They are formed when the
magma solidifies in deep rock layers before reaching
the surface land. Eg: granite, diorite, gabbros, etc.
They are found under the highlands of Rwanda and
they appear on the steep slopes. They are used as
queries to get stones, sand, etc.
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13. 2. Sedimentary rocks: rocks are formed from weathered and eroded materials
of the already existing rocks.
• Mechanically formed because deposited by running water in the valleys
and in depression where they are known as alluvium. Eg: silt, sand,
sandstones, mudstones, etc.
• Organically formed sedimentary rocks by decomposition of organic matter.
Ex. Limestone in Bugarama plain and close to Nyabarongo valley near to Kigali;
Peat, coal in most of swamps of Rwanda and Methane gas in Lake Kivu.
3. Metamorphic rocks: They are formed from either igneous or sedimentary
rocks under the influence of greater pressure and heat. Most of metamorphic
metamorphic rocks are found under the highland of Rwanda because caused
caused by pressure and heat from compression tectonic forces and molten
molten rocks in motion under the crust (Birunga region). Eg: quartzite, slate,
slate, gneiss, schist, hornblende,
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16. In Rwanda, there are several quarries where we exploit metamorphic rocks.
Almost 80% rocks of Rwanda are metamorphic and igneous origin. These
rocks found in Rwanda contain minerals necessary for economic development
of Rwanda.
Importance of rocks and minerals
Soil formation: rocks are parent material out of which soil particles are
Construction and building: some rocks of the earth’s crust are used in
construction and building activities;
Tourism: some rocks constitute beautiful landscape and hence attract
Energy: some rocks act as a source of energy needed to run industrial
Example: coal.
Fertilizers: rocks are very useful in the manufacturing of fertilizers. For
phosphate bearing rocks are used to make phosphate fertilizers.
Mining: Some rocks contain valuable minerals which are sources of foreign
exchange.
Salt rocks are edible.
Source of water, some ore used as ornaments
Millstones and grindstones
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17. Igneous rocks are characterised by the following features
• They are formed after the cooling and solidification of molten material.
material.
• They have a crystal appearance after cooling and solidification.
• They do not have strata or layers.
• They have no fossils.
Metamorphic rocks are characterised by the following features.
• They are harder and more compact than primary pre-existing rocks.
• The minerals in these rocks are recrystallised.
Sedimentary rocks are characterised by the following features:
• They have fossils.
• They have both inorganic and organic materials.
• They have no crystalline look because they do not form under the
influence of heat.
• They have rock layers known as strata as a result of the different and
successive deposition of sediments at different intervals 17
20. Revision questions
1. Define a rock.
2. State the three types of rocks found in Rwanda.
3. With a detailed explanation show how the following rocks were formed in
Rwanda.
a) Igneous rocks
b) Sedimentary rocks
c) Metamorphic rocks
4. Describe the characteristics of the different types of rocks.
5. Explain the economic importance of rocks.
6. In relation to the geology of Rwanda, write short notes on the young volcanic
rocks.
7. “Rocks are good and bad” discuss this statement in relation to the Rwandan
context.
8. Distinguish between rocks and minerals.
9. With specific examples, cite various minerals found in Rwanda.
10. Explain their contribution to the economic development of Rwanda
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Dynamic- due to pressure change (Kinetic or regional metamorphism). The pressure is caused by compressional force which cause earth movements and bring about mountain building
Thermal- due to intense heat (Contact metamorphism). Rocks change physically and chemically as a result of great heat originating from molten rock or magma.
Thermal-dynamic a combination of heat and pressure.
limestone helps in cement making, clay is used to manufacture bricks and tiles, granite broken into pieces can be used to make tarmac roads.
Examples are Ibere rya Bigogwe (Bigogwe Breast), Urutare rwa Ndaba (Ndaba Rock) and Urutare rwa Kamegeri (Kamegeri Rock).
