Rocks and Minerals

Identifying rocks and minerals

Rocks

Naturally occurring aggregate of mineralsLithosphere (Earth’s crust made of rocks)Three main types igneous, metamorphic and

sedimentaryPetrology is the scientific study of rocks. Does not have a fixed chemical composition.

Igneous Rocks

• Crystallise from molten material either above (volcanic) or below (plutonic) the Earth’s surface• Characterised by interlocking crystals• Volcanic rocks fine-grained

Plutonic rocks coarse-grained

Image sources:

http://www.fs.fed.us/r2/gmug/permits/grand_valley/gv_rock.shtml

http://www.beg.utexas.edu/mainweb/publications/graphics/granite.htm

Metamorphic Rocks

• Formed as a result of heat and pressure being applied to pre-existing rocks

• Characterised by foliation• Structure where crystals

align perpendicular to the direction of pressure

• Classified by texture and mineral/chemical assemblage.

Image Source : http://www.cropsoil.uga.edu/soilsandhydrology/Important%20Rocks%20&%20Minerals.htm

Sedimentary Rocks

• Formed when sediments are cemented together at or near the surface of the Earth

• Sediments formed as a result of chemical or mechanical weathering, erosion, transportation and deposition.

• Commonly form layers as sediment is deposited following erosion and transportation

• May contain structures to indicate way-upness!

Image source: http://www.edupic.net/geo.htm

Classifying Sedimentary Rocks

Breccia Conglomerate Sandstone

Halite Limestone Coal

Minerals

• Naturally occurring substance formed through geological processes

• Have a characteristic chemical composition, a highly ordered atomic structure and specific physical properties

• Range in composition from pure elements and simple salts to very complex silicates with thousands of known forms

• Study of minerals is called mineralogy

• Can be mined and processed to obtain constituent metals

Image Source: http://en.wikipedia.org/wiki/Mineral

Rocks v Minerals- What’s the difference?

• A mineral is made up of one substance that under normal circumstances would form crystals.

• Rocks are made up of minerals. Most rocks have several types of minerals in them, but some have only one type of mineral. For example, sandstone is mostly quartz.

Examples:• Minerals: Quartz, feldspar and mica.

Rocks: Granite, pegmatite, shale, slate, gneiss, schist (all made of quartz, feldspar and mica)

• Mineral: Calcite Rock: Limestone and marble (made of calcite)

• Minerals: Plagioclase feldspar and augiteRock: Basalt (oceanic volcanic rock made of plagioclase and augite)

Source: http://borntoexplore.org/ryan/rocksvs.htm

Task

Identify the samples provided as either rocks or minerals, justifying your response for each.