geology

What is a mineral?

Minerals are naturally occurring elements or compounds with fixed properties.

What is a rock?

Rocks are naturally occurring materials formed of minerals or fragments of rocks or fossils.

What is a fossil?

Fossils are any preserved sign of past life, more than 10,000 years old.

How many different minerals are found from the earth and how many occur commonly?

There are several thousand different minerals but only about thirty occur commonly.

How many minerals make up a rock?

Some rocks, such as meta-quartzite are made up of only one mineral (Quartz), but most have a number of different minerals held together (Quartz, feldspar and mica make up granite).

What are the eight elements present in large quantities in the earth's crust?

Oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium.

What elements make up the greatest percentage of the earth's crust?

Oxygen (47%) and silicon (28%).

Name the seven most common types of rock forming minerals.

Quartz (pure silicate SiO2), Feldspar (a range of silicates containing Al, Na, K, and Ca), Mica (complex silicates), Amphibole (complex silicates - hornblende), Pyroxene (silicates rich in Mg, Fe and Ca - augite), Olivine (silicate of Mg and Fe - MgFeSiO4), Calcite (calcium carbonate CaCO3).

Give the chemical formula for the following minerals:

Haemitite

Fe2O3

Malachite

CuCO3Cu(OH)2

Galena

PbS

Halite (rock salt)

NaCl

Gypsum

CaSO42H2O

Give examples of minerals formed by the following:

Crystallisation from a melt

Quartz, feldspar, mica.

Metamorphic recrystallisation

Calcite, garnet

Crystallisation from solution in evaporating water.

Halite

Crystallisation as cement from flowing pore waters

Quartz, calcite.

Crystallisation from hydrothermal fluids

Quartz, calcite, ore minerals, haematite, galena.

When are minerals valuable?

If they contain metals (ores, haematite, galena, gold) or have properties such as being rare, hard, lustrous, that cause them to become precious stones (Quartz, (amethyst) diamond.

What overall shapes can crystals form?

Tabular, acicular (needle), bladed, fibrous, reniform habits.

What observations would you use to identify minerals?

Shape, colour, streaks, lustre, hardness, cleavage, reaction to acid, specific gravity, magnetism, taste.

How are sedimentary rocks formed?

Sedimentary rocks are formed from deposits of material which has originally come from older rocks or living organisms.

Give the main examples of sedimentary rock.(5)

Breccia, conglomerate, sandstone, shale, limestone.

What properties do you investigate to identify the type of sedimentary rock?

Colour, texture(grain size/sorting and shape), and reaction with acid.

How are clastic sedimentary rocks formed?

They are formed from material which has been transported as actual pieces of rock and minerals eg. Pebbles, sand grains, clay minerals etc.

How are Chemical and organic sedimentary rocks formed?

These are mainly formed from material which was transported as a solution dissolved in water.

Give an example of a chemical sedimentary rock.

Halite (rock salt) can be formed by chemical precipitation as sea water evaporates.

Give an example of an organic sedimentary rock.

Coal, or as sea shells grow they extract dissolved CaCO3 from the water to build the shells and eventually a deposit of such shells may form a sedimentary rock.

Sedimentary rock type is dependant upon the environment of deposition.

What types can be found in shallow marine?

Limestone, sandstone, and conglomerates.

What types can be found in deep marine?

Turbidites, black shales.

What types in land?

Shale, sandstone, coal - deposited by rivers

Breccias, desert sandstone - deposited by wind and rivers

Halite - evaporation of saline water

Glacial till - deposited by melting ice.

What is lamination?

Small scale bedding where individual layers are only millimetres thick.

What is cross bedding?

Structure of coarse grained sediments such as sandstones, consisting of a set of tilted beds, cut by a younger set, caused by changes in direction of water currents or wind.

What is graded bedding?

Structure in clastic sediment where the larger class have settled to the base of the bed and the smaller to the top. Found in turbidites.

What are ripple marks?

A set of ridges and troughs formed on the sand or mud surface by the action of water currents.

What are desiccation cracks?

These structures are fairly common in sediments from lakes and lagoons which dried out from time to time.

What past environments do the following fossils show:

Reef-building corals

Marine, shallow, warm

Trilobite and ammonite

Marine

Plants

Land, indicating past climate.

Trace fossils

Tracks indicating land, burrows indicating shallow water

How is porosity and permeability influenced in sedimentary rocks?

By being compacted (shale) or cemented (sandstone)

How are Igneous rocks formed?

When magma (molten rock) cools and solidifies. Mineral crystals begin to grow and interlock forming a hard crystalline rock.

Give 5 examples of igneous rock.

Granite, gabbo, rhyolite, dolerite, basalt, pumice, obsidian, agglomerate and volcanic ash (tuff)

How would you identify the type of igneous rocks?

Colour, crystal size and random crystal orientation.

What affects the crystal size in igneous rocks?

The cooling rate of the magma.

What rock is formed from free-flowing mobile lava?

Basalt

What type of volcano is produced from free-flowing mobile lava?

Shield volcanoes.

What rock is formed from slow-moving viscous lava?

Rhyolite

What shape of volcano is produced from slow-moving viscous lava?

Stratovolcano, narrow, steep-sided cones.

What is a dyke?

Formed by magma filling fissures formed by the stretching of the surrounding rock (host rock).

How does a sill differ to a dyke?

Formed in same way but whereas dykes are steeply inclined and cut across structures in the country rock, sills are gently inclined and intrude planes of weakness in the rock.

What is a pluton?

A large magma chamber. The largest of which are called batholiths and are found in the core regions of mountain belts.

How is pillow lava formed?

Where lava is poured out into water, the lava is chilled rapidly forming a hardened skin around the outside of the structure.

What is columnar jointing?

This is formed during the cooling and contraction of thick flows. The contraction causes cracks to occur and the rock separates into a large number of vertical (usually 6 sided) columns.

How are metamorphic rocks formed?

Metamorphic rocks are formed when heat or pressure causes rocks to change.

During metamorphism, what elements are added or taken away from the original rock?

None, the original elements are simply rearranged.

How does schist form?

During the development of mountain chains when high pressure and moderately high temperatures occur, mudstones and shales can reform into schist.

How does slate form?

With high pressure but relatively low temperatures, mudstones and shale are changed into slate.

How does marble form?

The calcite in limestones recrystallises due to thermal and regional metamorphism and marble is produced.

How can you identify metamorphic rocks?

Texture, crystal size and orientation, and acid reaction.

What does the rock record show?

The evidence of tectonic activity.

What terms are used to describe and measure fold structures?

Dip and strike measurements of: symmetrical, asymmetrical, open, tight, rounded and angular shapes.

What causes folding?

Compressional tectonic stress.

What causes faulting?

Faulting occurs when rocks are fractured by tectonic stress (compressional, tensional, shear)

What are unconformities?

Unconformity is produced when the deposition of sediments is interrupted.

What is the principle of Uniformitarianism?

The present is key to the past - that the geological record was the result of a long series of events similar to those of the present day.

How can rocks be dated?

They can be dated and correlated using fossils.

How are Cephalopoda divided?

Goniatites - Upper Palaeozoic period

Ceratites - Triassic age

Ammonites - Jurassic and Cretaceous

How are the stipes and thecae of Graptolites useful in dating rocks

Evolution involved the number of stipes reducing and the form and arrangement of thecae changing over time.

Why are Graptolites useful to geologists?

They evolved rapidly, so each particular species only lived for a relatively short time. They were numerous and free-flowing so fossils are widely distributed. They first appeared in the Cambrian and became extinct in the Lower Carboniferous.

What radioactive elements can be found in feldspar or mica?

Very minute traces of rubidium or K40.

What is meant by half-life?

This is the time taken for half the parent atoms to decay into daughter atoms.

Why can't radio-carbon dating be used in most geology?

Radioactive forms of carbon have short half-life and so can only be used for materials less than 50,000 years old.

Explain Physical weathering.

Occurs where physical forces cause the rocks to disintegrate into smaller pieces. It happens mainly as a result of changes in temperature, especially in deserts, high mountains or polar regions.

Explain Chemical Weathering.

Occurs where chemical reactions cause the minerals in the rock to alter and decompose.

Why does chemical weathering occur mainly in warm wet climates?

The warmth increases the rate of chemical reaction and water allows chemical substances to be carried in solution.

What does the chemical weathering of granite produce?

Sand, clay and soluble material.

What causes the chemical weathering of limestone?

Rain water that has become acidic.

Give two examples of Biological weathering.

Tree roots can split rocks.

Burrowing animals can help break up rocks.

How is the weathered rock debris transported to a different site?

By gravity, by water in rivers and streams, by water in the sea, by glacial ice, by wind.

Erosion involves the transportation of what?

Solid weathering products by water, wind, ice or gravity.

What debris accumulates at the bottom of slopes due to gravity?

Scree.

What influences the size, shape and sorting or any new sediment caused by weathering or erosion?

The energy of the transporting medium, the depositional environment and time.

How can we tell the cause of a valley formation?

From the shape of the valley.

What causes V shaped valleys?

River erosion in upland areas.

What causes U shaped valleys?

Glacial action.

Valleys in lowland areas usually have?

Wide flat flood planes.

How can human activity modify the landscape?

Quarries and gravel pits, past mining activity, cuttings/tunnels excavated for roads and railways which are subject to landslides.

How can landscaping help restore the countryside?

Country parks on brownfield mining/quarrying sites.