Minerals And Rocks (Advanced)

Physical Characteristics

Minerals are naturally occurring inorganic substances with a definite chemical composition and crystalline structure. Their physical characteristics include:

• Color – Appearance of the mineral in reflected light.
• Streak – Color of the mineral in powdered form.
• Hardness – Measured by Mohs scale (1 = Talc, 10 = Diamond).
• Lustre – Appearance in reflected light (metallic or non-metallic).
• Cleavage – Tendency to break along definite planes.
• Fracture – Manner in which a mineral breaks other than along cleavage planes.
• Specific Gravity – Ratio of a mineral’s density compared to water.

Metallic Minerals

These minerals contain metal in raw form and are typically hard, lustrous, and conductive. They are further divided into:

• Ferrous Minerals – Contain iron (e.g., hematite, magnetite, pyrite).
• Non-Ferrous Minerals – Do not contain iron (e.g., bauxite, copper, zinc, lead).

Non-Metallic Minerals

These minerals do not contain metals and are used in industries or as decorative stones. Examples include:

• Mica – Used in electronics and insulation.
• Limestone – Used in cement and steel industries.
• Gypsum – Used in construction (plaster).
• Quartz – Used in glass and ceramics.

Rocks

Igneous Rocks

Formed by solidification of molten magma. Two types:

• Intrusive (Plutonic) – Cool slowly beneath Earth’s surface (e.g., granite).
• Extrusive (Volcanic) – Cool rapidly on surface (e.g., basalt).

Sedimentary Rocks

Formed by deposition and compaction of sediments. Often contain fossils. Examples:

• Sandstone, shale, limestone.

Metamorphic Rocks

Formed from existing rocks under heat and pressure. Examples:

• Marble (from limestone), slate (from shale), gneiss (from granite).

Rock Cycle

The rock cycle is a continuous process of transformation of rocks from one type to another due to Earth’s internal and external forces:

1. Igneous rocks break down into sediments, forming sedimentary rocks.
2. Sedimentary and igneous rocks may undergo metamorphosis under pressure and heat.
3. Metamorphic rocks may melt into magma and again cool to become igneous rocks.

This cycle keeps the Earth’s crust dynamic and constantly changing.