Science revision-geology year 8 (copy)

Definition of a Mineral

A naturally occurring, inorganic solid with a definite chemical composition and an ordered crystalline structure.

Mohs’ Hardness Scale

A scale from 1 (softest) to 10 (hardest) used to contrast mineral hardness.

Physical Weathering

The physical breakdown of rocks into smaller pieces without changing their chemical composition.

Chemical Weathering

The alteration of the internal mineral structure of rocks through chemical reactions.

Biological Weathering

Disintegration caused by living things, such as plant roots splitting rock.

Definition of Erosion

The process of moving weathered rock and soil particles from one location to another by wind, water, ice, or gravity.

Intrusive Igneous Rocks

Rocks formed deep underground when magma cools slowly.

Extrusive Igneous Rocks

Rocks formed at or near the surface when lava cools rapidly.

Formation Process of Sedimentary Rocks

Weathering breaks down rocks, erosion transports sediments, deposition lays sediments in layers, compaction squeezes them, cementation glues minerals together.

Characteristics of the Earth’s Crust

Solid rock (silicates) with a thickness of 5–70 km and temperatures up to 400°C.

Difference between Magma and Lava

Magma is molten rock below the Earth’s surface, while lava is molten rock that has erupted onto the surface.

Foliated Metamorphic Rocks

Rocks with visible mineral bands or layers aligned by directional pressure.

Non-Foliated Metamorphic Rocks

Rocks with a massive, crystalline structure lacking distinct bands.

Lustre in Minerals

How light reflects off the surface of a mineral (e.g., metallic, glassy, dull).

Streak of a Mineral

The color of a mineral in powdered form, tested by scratching it against a porcelain plate.

Cleavage of a Mineral

The tendency of a mineral to break along flat, parallel planes of structural weakness.

Types of Sedimentary Rocks

Clastic, Chemical, and Organic (Biochemical), based on their formation process.

Deep Dive: Grinding Technique

A process where raw stone is rubbed against a harder rock using water as a lubricant to sharpen and polish.