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Earth Materials Rocks and Minerals
Mineralogy:
The Study of Minerals and their Proper8es
A Mineral…
• Occurs naturally
• Is a solid
• Is a pure substance (element or compound)
• Has atoms arrange in an orderly pa:ern (crystalline)
• Is inorganic (not formed by any process involving plants or animals)
• The most common elements that make up minerals are oxygen, silicon, aluminum, iron, calcium, potassium, and magnesium
• There are over 2000 known minerals; most are rare.
• Common minerals that make up most of the Earth’s crust are called ROCK-‐FORMING MINERALS
• Most minerals are compounds
(i.e., halite = NaCl, Galena = PbS)
• A few minerals are made up of only ONE element, and are called NATIVE elements
(i.e., gold, copper, silver, sulphur, carbon)
Mineral Iden8fica8on
• Minerals are usually idenNfied using physical properNes, although some simple chemical tests may also be used.
Colour
• First, and most easily observed property • Some minerals have dis8nc8ve colours (i.e., malachite, sulphur)
• However, many different minerals have similar colours
• Weathering may also alter the colour of minerals
Lustre • The way a mineral shines in reflected light.
• Either metallic (like polished metal) or non-‐metallic
• Non-‐metallic lustre may be further described as vitreous (glass-‐like), pearly, greasy, dull, earthy, etc.
Crystal Shape
• When minerals have Nme and room to form, their parNcles arrange themselves into flat-‐faced, regularly shaped crystals.
• However, most mineral grains are too small or imperfect to idenNfy.
Streak
• The colour of a mineral’s powder when it is rubbed against a streak plate
• Metallic minerals give dark streaks (brown, grey, black)
• Nonmetallic minerals give light streaks
Cleavage/Fracture
• A mineral exhibits cleavage if it breaks along flat surfaces when hit with a hammer.
• A mineral exhibits fracture if it splits into uneven or curved surfaces
Hardness • A mineral’s resistance to being scratched.
• Moh’s hardness scale: measure of how hard a mineral is compared to a standard set of minerals, ranging on a scale from 1 to 10 (soXest = talc (1), hardest = diamond (10)).
• Prospector’s Scale:
Fingernail = 2.5
Penny = 3
Steel = 5.5
Glass = 6
Specific Gravity
• The relaNve density of a mineral.
• RaNo of mineral’s weight to an equivalent amount of water.
• Specific gravity of non-‐metallic minerals is generally < 3
• Specific gravity of metallic minerals is generally > 5
Acid Test
• When calcite is exposed to acid, it fizzes
• Gas produced is carbon dioxide
Magne8sm
• Some minerals containing iron are magne8c and will be a:racted to a magnet (ie., magneNte)
Other Proper8es
• Taste (i.e., halite – rock salt)
• Fluorescence (glows in ultraviolet light)
• RadioacNvity
• Double Refrac8on
Mineral Groups
• All minerals can be classified as either silicate or non-‐silicate minerals
Silicates
• Silicate minerals contain atoms of silicon (Si) and Oxygen (O)
• Some only contain silicon and oxygen
(i.e., quartz – SiO2)
• most also contain one or more other elements
(i.e., feldspar: ( KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8)
• Feldspar is the most common mineral in the earth’s crust, followed by quartz
• Silicates make up 96% of the Earth’s crust
Non-‐silicates
• 4% of the Earth’s crust is made up of non-‐silicate minerals (meaning they don’t contain silicon)
• Can be further classified as: – Carbonates – contain carbonate (CO3) group
– Halides – halogens (Cl, F) with Na, K or Ca – NaNve elements
– Oxides – contain oxygen, but not silicon
– Sulfates – contain sulphate ( (SO4) group
– Sulfides – contain sulfur
PETROLOGY
The Study of Rocks and their Forma8on
Principles of Uniformitarianism:
1. Geological processes now at work were also acNve in the past.
3. Physical features of the Earth were formed by these processes over long periods of Nme.
In other words, the rocks we see around us were formed in the past by the same geological processes we see around us today.
Rock Types and the Rock Cycle
• A rock is a group of minerals bound together (i.e., it is usually a mixture).
There are three types of rock: • igneous rock – formed when molten rock cools
• sedimentary rock – formed from weathered and eroded rock that is deposited and cemented together into new rock.
• metamorphic rock – formed when exisNng rock undergoes intense heat and pressure that alters the rock’s composiNon and characterisNcs.
Igneous Rocks
• “igneous” comes from the Greek word for fire.
• Deep inside the earth, the temperature is very high and the rock there is in liquid form called magma.
• As magma pushes towards the Earth’s surface, it starts to cool and turn into solid igneous rock.
• Igneous rocks that cool slowly deep in the Earth are called intrusive or plutonic igneous rocks.
• Other igneous rocks form when magma erupts from a volcano, or reaches the surface through long cracks in the crust. Magma is called lava when it reaches the Earth’s surface. These are called extrusive or volcanic igneous rocks.
• Igneous rocks are classified by composi8on (the minerals it contains) and texture (crystal size).
Composi8on of Igneous Rocks
• Igneous rocks form from two main types of magma:
– FELSIC
– MAFIC
Felsic Rocks:
• Magma with a high percentage of silica (SiO2) and li:le calcium, magnesium or iron.
• Felsic magma is thick and slow-‐flowing
• Forms light-‐coloured rocks
• Most plutonic rocks are felsic
Mafic Rocks:
• Magma with a low silica content, with higher amounts of calcium, magnesium and iron.
• Ho:er and thinner than felsic magma
• Forms dark-‐coloured rocks
• Most volcanic rocks are mafic
Texture of Igneous Rocks
• Depends on size of mineral crystals in the rock.
• Crystal size depends on how fast magma hardens
• LONGER = LARGER
• Plutonic rocks cool slower, therefore coarse grains
• Lava hardens rapidly forming 8ny crystals • Lava that cools super-‐quick forms rocks with no crystals
• Porphyry: a rock with 2 stages of cooling, so that it has both large and small crystals.
Sedimentary Rocks
• most of the earth’s surface is covered in sedimentary rocks
• there are three types of sedimentary rocks: – clasNc -‐ made from fragments of other rocks. – chemical -‐ formed from precipitates falling out of soluNon.
– organic -‐ formed from remains of plants and animals.
Clas8c Sedimentary Rocks
• form when rocks weather (break apart). • That material is eroded (carried away) and later deposited in another locaNon.
• Layers of sediment undergo pressure and cementaNon to eventually form sedimentary rocks.
• ClasNc rocks are classified by “sorNng” (size of parNcles)
• Conglomerate: made up of pebbles and sand
• Sandstone: mainly grains of quartz
• Shale: Nny flakes of clay cemented together
Chemical Sedimentary Rocks
• Form when sea, lake, swamp or underground waters evaporate or change temperature, causing dissolved minerals to fall out of soluNon.
• Examples include some limestones, rock salt and rock gypsum.
Organic Sedimentary Rocks
• Formed from the remains of plants and animals • Shell-‐producing organisms such as clams, mussels or coral are made up mostly of calcite – the mineral that makes up limestone. When they die their shells pile up on the floor of the water body, and eventually cement together to form limestone.
• Coal is formed from decayed plants that are buried and compacted into ma:er that is mostly carbon.
Metamorphic Rocks
• Heat and pressure can cause certain minerals to change into other minerals.
• Minerals may also change in size or shape, and they may separate into parallel bands.
• Hot magma may circulate through a rock, dissolving some minerals and deposiNng others.
Types of Metamorphism:
• Contact metamorphism – when hot magma pushes through exisNng rock, causing changes in the structure and composiNon of surrounding rock.
• Regional metamorphism – movement of tectonic plates creates tremendous heat and pressure at plate boundaries, changing minerals into rock.
Classifica8on of Metamorphic Rocks:
• Made according to the texture of the rock (foliated or non-‐foliated), and the composiNon of the rock.
Foliated Metamorphic Rocks:
– Extreme pressure fla:ens mineral crystals in rock and pushes them into parallel bands
– Minerals of different densiNes separate into bands, oXen producing alternaNng dark and light layers.
– Examples included slate, schist and gneiss
Non-‐Foliated Metamorphic Rocks
– No “banding” or layers are observed
– Examples include quartzite and marble
The Rock Cycle