Rocks and minerals How are they formed THREE

Rocks and minerals How are they formed?

THREE TYPES OF ROCKS Igneous Sedimentary Metamorphic

Igneous Rocks formed from magma that has cooled and solidified

1. Intrusive (or plutonic) Formed by slow cooling of magma in Earth’s crust Made of very large crystal that are visible to the naked eye Eg. gabbro

2. Extrusive (or volcanic) Formed when a volcano erupts and the magma cools with the air or water Cools rapidly Made of microscopic crystals Eg. obsidian

3. Porphyritic Undergoes two cooling phases i. Slow: in Earth’s crust ii. Rapid: pushed out with magma, cools on surface Large and small crystals Eg. granite

Sedimentary rocks formed by sedimentation (rocks broken into pieces) of material at the Earth’s surface and in bodies of water sediments formed by erosion: the action of water, wind and glaciers fragmented then deposited over time, these fragments are compacted and cemented

Sedimentary Eg. limestone, sandstone

SEDIMENTARY

metamorphic Already formed igneous, sedimentary or metamorphic rock undergoes change Transformed by heat and pressure Occurs deep in Earth’s crust Eg. slate, quartz, marble

The rock cycle

Rock or mineral? Rocks Blend of various minerals Different sized and kinds of grains Minerals Pure, natural substance

Identifying minerals Magnetic Metallic ( lustre) Streak (colour) Hardness Density