ROCK FORMING MINERALS
By the end of the lesson, the student should be able to:
i. Name common rock forming minerals
ii. Classify minerals into major mineral groups
iii. Describe physical properties of common rock forming minerals
Mineral – a naturally occurring, inorganic, solid that has a definite chemical composition and
crystal structure. Rock on the other hand is a naturally occurring and coherent aggregate of one
or more minerals.
Rock Classification
Rocks are classified based on their formation and origin. Many kinds of rocks are composed of
minerals. Some rocks are monomineralic meaning they are composed of one mineral (ex.
limestone-calcite). Some rocks are polymineralic meaning they are composed of two or more
minerals (ex. granite). There are almost 3000 types of minerals, but only 8 of these minerals
make up 90% of the rocks of Earth’s crust. The 3 groups of rocks are: Sedimentary, Igneous and
Metamorphic
Sedimentary Rocks
Sedimentary rocks are rocks that usually form in layers from the accumulation of sediments,
organic material, or chemical precipitates. Most sedimentary rocks are made up of solid
sediments that have been weathered from other rocks. The weathered sediments are then eroded
(transported) by water, wind, and glaciers. Eventually the eroded sediments are deposited at new
locations either in water or on land. Most sedimentary rocks form in layers underwater in lakes,
seas or oceans.
1
, Some common sedimentary rocks are: Limestone, Chalk, Clay, Sandstone, Shale among others.
Sedimentary rocks can further be classified into the following categories.
Organic Sedimentary Rocks
This rock type mainly comprises coal and limestones, which are formed due to the accumulation
and deposition of dead plants and animals in rock layers. Peat is accumulated plant material,
lignite is brown and soft while anthracite coal is soft coal that meta morphed into hard coal
Clastic Sedimentary Rocks
2
By the end of the lesson, the student should be able to:
i. Name common rock forming minerals
ii. Classify minerals into major mineral groups
iii. Describe physical properties of common rock forming minerals
Mineral – a naturally occurring, inorganic, solid that has a definite chemical composition and
crystal structure. Rock on the other hand is a naturally occurring and coherent aggregate of one
or more minerals.
Rock Classification
Rocks are classified based on their formation and origin. Many kinds of rocks are composed of
minerals. Some rocks are monomineralic meaning they are composed of one mineral (ex.
limestone-calcite). Some rocks are polymineralic meaning they are composed of two or more
minerals (ex. granite). There are almost 3000 types of minerals, but only 8 of these minerals
make up 90% of the rocks of Earth’s crust. The 3 groups of rocks are: Sedimentary, Igneous and
Metamorphic
Sedimentary Rocks
Sedimentary rocks are rocks that usually form in layers from the accumulation of sediments,
organic material, or chemical precipitates. Most sedimentary rocks are made up of solid
sediments that have been weathered from other rocks. The weathered sediments are then eroded
(transported) by water, wind, and glaciers. Eventually the eroded sediments are deposited at new
locations either in water or on land. Most sedimentary rocks form in layers underwater in lakes,
seas or oceans.
1
, Some common sedimentary rocks are: Limestone, Chalk, Clay, Sandstone, Shale among others.
Sedimentary rocks can further be classified into the following categories.
Organic Sedimentary Rocks
This rock type mainly comprises coal and limestones, which are formed due to the accumulation
and deposition of dead plants and animals in rock layers. Peat is accumulated plant material,
lignite is brown and soft while anthracite coal is soft coal that meta morphed into hard coal
Clastic Sedimentary Rocks
2
