Week 4: How to build a planet: minerals and rocks Flashcards
What is a mineral?
-naturally occurring chemical substance
-has a definite atomic structure and chemical formula (specific chemical composition)
-crystalline, solid inorganic materials
What are the key physical properties of minerals, that can be used in their identification? What controls these properties?
All controlled by theri chemical composition
1. Colour= determined by chemical composition
2. Lustre= surface appearance
3. Hardness= strong chemical bonds result in hard minerals
4. Habit: the shape it takes
5. Cleavage= planes of weakness in mineral related to atomic structure
6. Fracture= tendency to break along irregular surfaces other than cleavage planes
7. Density= depends on atomic weight of atoms/ions and their closeness of packing
Silicate minerals you should be familiar with:
-quartz
-feldspar
-mica
-pyroxene
-amphibole
-olivine
-clay minerals
-garnet
Non-silicate minerals you should be familiar with:
-calcite
-dolomite
-gypsum
-halite
-magnetite
-pyrite
-hematite
What four mechanisms result in the formation of minerals?
- Cooling and crystallisation
- Evaporation and precipitation
3.Sold state transformation - Secretion by organisms
How are minerals grouped according to their chemical composition?
- Silicates= contain O and Si e.g. quartz (SiO2)
- Carbonates= contain C and O e.g. calcite (CaCO3)
- Oxides= contain O and metallic cations e.g. hematite (Fe2O3)
- Sulfides= contain S (but no O) and metallic cations e.g. pyrite (FeS2)
- Sulfates= contain S04 and metallic cations e.g. anhydrite (CaSO4)
- Halides= contain one of CI, F, I or Br (but no O)
- Hydroxides= contain OH
- Native elements= metals occurring as a single element, not in combination e.g. gold, silver, copper
What is quantitatively the most common group of minerals in the Earth’s crust?
Silicates
What is the building block of all silicate minerals?
Silicate tetrahedra- ploymerisation
How do the arrangement of the tetrahedra affect the structure of silicate minerals, and what are common mineral examples of each type?
- Islands= isolated tetrahedra, do not share any oxygens e.g Olivine and Garnet
- Single Chains= two of the three basal oxygens are bonded together (Si:O= 1:3) e.g. Pyroxene
- Double chains= two single chains that share oxygens where tetrahedra touch to form a double chain (Si:O= 2:7) e.g. amphibole
- Sheets= share 3 oygens along the base of the tetrahedra to form 2D sheets (Si:O= 2:5) e.g mica
- 3D Frameworks= all oxygens are shared between adjacent tetrahedra to form 3D framework (Si:O= 1:2) e.g quartz and feldspar
What is fractional crystallisation and how does it control the silicate mineral formed?
- minerals crystallize from a melt at diffrent temperatures
-as they crystallize they change chemical composition of remaining melt
-from mafic to felsic
(known as Bowens reaction series)
What is a rock?
-aggregate of mineral grains (or in some cases non-mineral solid matter e.g. glass, fossils)
-naturally occurring
-solid
-can be either crystalline or cemented
-can be very strong and durable
-some rocks are more resistant to weathering than others
How are rocks classified? What are the three common types of rocks?
Rocks are classified by their origin
1.Igneous
2. Sedimentary
3. Metamorphic
What is the main difference between igneous, sedimentary and metamorphic rocks in terms of their origins?
- Igneous rock= solidification from molten rock
- Sedimentary rocks= erosion and deposition of pre-existing rocks
- Metamorphic rocks= changes due to heat and/or pressure
How can texture be used to distinguish igneous, sedimentary and metamorphic rocks?
- Igneous= crystalline
- Sedimentary= non-crystalline and layered (layering due to grain size)
- Metamorphic=crystalline and layered (layering due to composition
What are the most common minerals found in igneous, metamorphic and sedimentary rocks?
- Igneous:
-quartz
-feldspar
-mica
-pyroxene
-amphibole
-olivine - Sedimentary:
-quartz
-clay minerals
-feldspar
-calcite
-dolomite
-gypsum
-halite - Metamorphic:
-quartz
-feldspar
-mica
-garnet
-pyroxene
-staurolite
-kyanite
How do intrusive and extrusive igneous rocks form?
Intrusive= trapped, cooled and solidified beneath the surface
Extrusive= erupted from a volcano and cooled at Earth’s surface (lavas and ashes)
How are igneous rocks classified?
By their texture
Granite= coarse-grained/slow cooling
Basalt= fine grained/fast cooling
What controls the texture of an igneous rock?
Granite= coarse grained slow cooling
Basalt= fine grained fast cooling
What is meant by mafic and felsic? What minerals do these rocks contain? (igneous)
felsic:
-rich in silica, low in Mg
(quartz, feldspar, muscovite)
mafic:
-poor in silica, rich in Mg
(biotite, amphibole, pyroxene, olivine)
Where are igneous rocks found?
areas of high tectonic activity
What is a clastic sedimentary rock? How is grain size used to name a clastic rock?
Clastic= (detrital)
-allochthonous
-physical processes
How does weathering affect the minerals present in a clastic sedimentary rock compared to the parent igneous or metamorphic rock?
Feldspar:
igneous/metamorphic= 60%
sedimentary= 15%
Quartz:
igneous/metamorphic= 25%
sedimentary= 50%
Ca, Mg/Fe silicates:
igneous/metamorphic= 15%
sedimentary= 0%
How do evaporites and limestones form? (sedimentary)
Evaporites formed due to evaporation of a saline lake
Why has the composition of limestones changed through time? (sedimentary)
due to changes in deposition of carbonates over geological time
What is diagenesis and lithification? (sedimentary)
Diagenesis= processes occurring during lithification
Lithification= conversion of sediment to rock
Where are sedimentary rocks found?
deposited as layers of sediment in land or in water
What is metamorphism? How does it cause rocks to change?
changed by the action of heat and or pressure
can cause minerals to recrystallize e.g limestone to marble
What is metamorphic grade? How does a mudstone change as metamorphic grade increases?
as pressure and heat increases chemical reactions occur changing mudstone into migmatite (from low grade to high grade)
Where does metamorphism take place?
continental crust
