26/04/2026
Useful information.
Diploma students take note 🙂
ROCK-FORMING MINERALS
INTRODUCTION
Rock-forming minerals are the most abundant minerals in the Earth’s crust. They combine in different ways to form various types of rocks. The diagram below presents these minerals in a tree-like structure, showing their major groups and examples.
Rock-forming minerals are naturally occurring inorganic substances that make up rocks. They have definite chemical compositions and crystalline structures.
MAJOR GROUPS OF ROCK-FORMING MINERALS
The image below organizes rock-forming minerals into several important groups:
1. SILICATE MINERALS
These are the most abundant minerals and are made up of silicon and oxygen.
a. FELDSPARS
~ Examples: Potash feldspar, Soda-lime feldspar
~ Importance: Most abundant mineral group in the Earth’s crust
~ Found in: Igneous rocks like granite
b. QUARTZ
~ Types: Crystalline and Non-crystalline
~ Characteristics: Hard, resistant to weathering
Found in: Sandstones, granites
2. FERROMAGNESIAN MINERALS
Rich in iron (Fe) and magnesium (Mg), usually dark in colour.
a. PYROXENES
~ Examples: Augite, Diopside, Enstatite
~ Characteristics: Dark, dense minerals
~ Found in: Basalt and gabbro
b. AMPHIBOLES
~ Examples: Hornblende, Actinolite, Tremolite
~ Characteristics: Elongated crystals
~ Found in: Metamorphic and igneous rocks
3. SHEET SILICATES
• MICAS
~ Examples: Biotite, Muscovite, Phlogopite
~ Characteristics: Split easily into thin sheets (perfect cleavage)
~ Uses: Electrical insulation, heat resistance
4. OTHER IMPORTANT MINERAL GROUPS
a. GARNETS
~ Examples: Pyrope, Almandine, Andradite
~ Characteristics: Hard, often used as gemstones
~ Found in: Metamorphic rocks
b. OLIVINE GROUP
Green-colored minerals
~ Found in: Mantle rocks and basalt
c. ZEOLITES
Hydrated minerals
~ Used in: Water purification and industrial processes
d. CALCITE
• Main component of limestone
• Reacts with acids
e. DOLOMITE
Similar to calcite but contains magnesium
f. CHLORITES
• Green minerals found in low-grade metamorphic rocks
g. SERPENTINE
Soft, green minerals formed from alteration of olivine
h. TOURMALINE & STAUROLITE
Common accessory minerals in metamorphic rocks
From the Diagram:
• Minerals are grouped based on chemical composition and structure
• Silicates dominate the Earth’s crust
• Some rocks may lack definite minerals (e.g., volcanic glass)
• Most rocks contain combinations of these mineral groups
IMPORTANCE OF ROCK-FORMING MINERALS
• Help in identifying rock types
• Useful in understanding Earth’s processes
• Provide raw materials for industries
• Used in construction and manufacturing
CONCLUSION
Rock-forming minerals are fundamental to geology. Understanding their classification and characteristics helps geologists interpret the origin, composition, and history of rocks in the Earth’s crust.
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