Describe the characteristics and types of primary rocks. (Answer in 150 words)

Primary rocks are igneous rocks, formed by the cooling and solidification of magma or lava. They are the original rocks from which sedimentary and metamorphic rocks develop.

Key characteristics

• They are generally hard, compact, crystalline and devoid of fossils.
• They commonly contain interlocking mineral grains and are resistant to erosion.
• They may be rich in metallic minerals and form important parent material for soils.

Types by mode and place of cooling

• Intrusive or plutonic: magma cools slowly beneath the surface, producing coarse crystals; granite and gabbro are examples.
• Hypabyssal: magma solidifies in shallow intrusions such as dykes and sills; textures are intermediate.
• Extrusive or volcanic: lava cools rapidly at the surface, producing fine-grained or glassy rocks; basalt, rhyolite and obsidian are examples.

Significance

Igneous rocks create plateaus, batholiths and volcanic landscapes, influence mineral availability and participate continuously in the rock cycle through weathering, burial and metamorphism.

Igneous; magma; lava; intrusive; extrusive; plutonic; volcanic; rock cycle.