1.1 Minerals Flashcards
What are minerals?
Substances with a definite chemical composition and atomic structure and formed by the inorganic processes of nature
What are minerals composed of?
Elements
What are the eight most common elements found in minerals?
- oxygen
- aluminium
- calcium
- potassium
- silicon
- iron
- sodium
- magnesium
What is the name of the mineral made from pure silica?
Quartz
What is the symbol for pure silica/quartz?
SiO2
What are the physical properties of minerals that are studied?
- colour
- streak
- lustre
- form or habit
- cleavage
- fracture
- hardness
- relative density
What are the chemical properties of minerals that are studied?
- acid test
* taste test
What does the colour of a mineral depend on?
The colours of the spectrum that it reflects
What does it mean, in terms of reflection of light, if a mineral is colourless?
It allows most light to pass through it
What is the name of a colourless quartz?
Rock crystal
What is the name of a purple quartz?
Amythyst
What is the name of a yellow quartz?
Citrine
What is the name of a brown quartz?
Smoky quartz
What is the name of a pink quartz?
Rose quartz
What is the name of a white quartz?
Milky quartz
What is the streak of a mineral?
The colour of a mineral’s powder
How is the streak of a mineral seen?
By rubbing it on a piece of unglazed porcelain (streak plate)
Is the colour of a mineral’s streak necessarily the same as its normal colour?
No
What colour streak does black haematite have?
Red
What happens if minerals are harder than the streak plate?
They will have no streak
What is the lustre of a mineral?
The amount and quality of light that it reflects
What terms can be used to describe lustre?
- metallic
- vitreous (glassy)
- adamantine
- dull
What is a metallic lustre?
The ordinary lustre of metals
What is a vitreous lustre?
The lustre of broken glass
What is an adamantine lustre?
The brilliant lustre of diamond
What is a dull lustre?
Having little or no lustre
What is the form or habit of a mineral?
The common shape a mineral takes
What terms are used to describe crystal structure?
- crystallised
- crystalline
- cryptocrystalline
- amorphous
What does it mean if a mineral is crystallised?
The mineral occurs as well developed crystals
What does it mean if a mineral is crystalline?
A confused mixture of imperfect crystals
What does it mean if a mineral is cryptocrystalline?
Mere traces of crystalline structure
What does it mean if a mineral is amorphous?
No crystalline structure - this is quite rare
What is the crystal structure of peridot?
Crystallised
What is the crystal structure of fluorite?
Crystalline
What is the crystal structure of gypsum?
Cryptocrystalline
What is the crystal structure of graphite?
Amorphous
What are other common shapes among minerals (not crystalline, crystallised etc.)?
- cubic
- rhombic
- hexagonal
- reniform (kidney shaped)
- nodular
- columnar
- fibrous
- foliated
What does it mean if a mineral is nodular?
Detached, rounded masses
What does it mean if a mineral is foliated?
Thin layers or lamellae
What is the cleavage of a mineral?
The tendency to split along definite planes, known as cleavage planes
What direction are cleavage planes in?
Parallel to crystal forms
How is cleavage described?
Good/poor
Types of cleavage?
- cubic cleavage - 3 directions
- rhombohedral - 3 directions
- basal cleavage - 1 direction
What is fracture?
The irregular way in which a mineral breaks apart
What are the 3 main types of fracture?
- uneven - rough surface
- hackly
- conchoidal
What is hackly fracture?
A surface studded with sharp and jagged elevations
What is conchoidal fracture?
Concave or convex surface with concentric lines (like a shell)
What scale is used to test hardness?
Moh’s scale
What does it mean if you can scratch a mineral with your fingernail?
It has hardness of less than 2.5
What does it mean if you can scratch a mineral with a copper coin?
It has a hardness between 3.5 and 2.5
What does it mean if you can scratch a mineral with a steel pin?
It has a hardness between 3.5 and 5.5
What does it mean if you can’t scratch a mineral with a steel pin?
It has hardness more than 5.5
What is the relative density of a mineral?
Shows the number of times heavier that mineral is than an equal volume of water
How to calculate relative density?
Mass of specimen in air (g) / water displaced by specimen (cm3)
What is the commonly used test for calcite?
Acid test
What is the most important mineral in limestone?
Calcite
How is an acid test carried out?
Dilute HCl dropped on the mineral, which bubbles and gives of CO2
What is the taste test used to identify?
Halite
Why is halite salty?
Composed of NaCl
How can minerals be formed?
- crystallisation from a melt
- metamorphic crystallisation
- crystallisation from solution in evaporating water
- crystallisation as a cement from flowing pore waters
- crystallisation from hydrothermal fluids
What type of rocks does crystallisation from a melt generally apply to?
Igneous rocks
How does crystallisation from a melt form minerals?
Minerals crystallise when magma cools to form igneous rocks
What happens when magma cools very rapidly?
Volcanic glass is formed
When will big crystals form?
When magma deep in the crust cools slowly
When will small crystals form?
When magma that pours out onto the surface of the crust cools rapidly
When will both big and small crystals form?
When magma cooling partly deep in the crust and partly on the surface
What minerals does granite contain?
- mica
- quartz
- feldspar
When does metamorphism occur?
When rocks are changed by an increase in temperature and/or pressure
Does metamorphism involve a liquid phase?
No - it is a change from one solid to another
Which minerals are formed by crystallisation from a melt?
- quartz
- mica
- feldspar
- olivine
- augite
Which minerals are formed by metamorphic recrystallisation?
- calcite
* garnet
Which minerals are formed by crystallisation from solution in evaporating water?
Halite
Which minerals are formed by crystallisation as cement from flowing pore waters?
- quartz
* calcite
Which minerals are formed by crystallisation from hydrothermal fluids?
gangue minerals:
- quartz
- calcite
ore minerals:
- haematite
- galena
In metamorphic recrystallisation, what does higher temperatures mean for crystal size?
Larger crystals
In metamorphic recrystallisation, what do higher pressures mean for crystal size?
Produce layering in the rock - foliation
What is evaporite?
Substances left behind from evaporation
When does a solution become saturated?
When it is heated by the sun
How is halite formed?
- minerals carried into lake in solution
- sun heats up lake waters
- evaporation of lake waters
- halite precipitated out from solution
How are minerals formed by crystallisation as a cement from flowing pore waters?
- when sediment deposited it will only become hard sedimentary rock if it is cemented by minerals
- water in pores between sediments carries dissolved minerals which are precipitated out between clasts
- minerals bind clasts together form the cement of the rock
What are the three main minerals that form cements in sedimentary rocks?
- stiperstones conglomerate - quartz
- wenlock limestone - calcite
- navajo sandstone - haematite
What is haematite also known as?
Iron oxide
Where are hydrothermal minerals deposited from?
Hot water solutions
How do hydrothermal minerals form?
From the heated waters given off by magma as it cools - these hot waters can dissolve and carry metals
What are the deposits of metallic minerals called?
Ores
When hot water solutions are cooled, how can the elements crystallise?
- in cavities or fissures as hydrothermal veins
* in between the grains of sediments as impregnations
What are gangue minerals?
The minerals in hydrothermal veins that are not ores and not of any value e.g. quartz and calcite
What happens when some minerals form at higher temperatures in hydrothermal veins?
This causes the vein to show the minerals as zones
How are minerals in sedimentary rocks most often found?
As clasts (grains)
Which characteristics of clasts in sedimentary rocks can determine how much transportation and erosion has taken place?
- size - given by the length of its long axis
- sorting - how close clasts are to being the same size
- roundness
- sphericity
What are the three main methods of prospecting for minerals?
- field mapping
- geophysical techniques
- geochemical techniques
What is field mapping?
Involves analysing geology of an area in a field, producing a field map and therefore suggested locations for mineral exploitation
What are the geophysical techniques of prospecting?
- magnetic surveys
- seismic surveys
- electrical surveys
What are magnetic surveys?
Using a magnetometer, ore bodies are picked out as they show a stronger magnetism as they are more able to take on the earth’s magnetic field
What are seismic surveys?
Using seisometers, they discover mineral reserves but are more widely used in the petroleum industry
What are electric surveys?
Ore bodies conduct an electric current more easily than other geological materials - a resistivity survey involves passing current through the crust to show location of ore body
What are the geochemical techniques of prospecting?
- soil and sediment sampling
* water sampling
How can soil and sediment sampling prospect minerals?
Soil and sediment are formed from breakdown of rock, so may contain evidence of ore bodies that lie beneath the surface
How can water sampling prospect minerals?
Water may contain small amounts of metallic elements that indicate water has passed over an ore body
What are the problems with prospecting using water sampling?
Water can be contaminated because concentrations of metals are low, and variations in acidity make interpretation difficult
What are the methods used to mine minerals?
- mining hydrothermal veins
- mining large ore bodies
- mining evaporite deposits
How are hydrothermal veins mined?
Using the adit and stope method
What is the adit and stope method of mining?
- adit - tunnel driven into hillside at a low angle to get to vein
- stope - tunnel dug along line of veins
- stope and adits join to create complex of tunnels in the mine
How can ore minerals be extracted when found in large bodies?
By the process of open cast mining - only for when ore is near the surface. Remove overlying rock.
How can halite be mined from evaporite?
When found near surface, use pillar and stall method
What is the pillar and stall method of mining in evaporite deposits?
Removing most of halite but leaving pillars so support roof of mine`
Why is halite good for the pillar and stall method of mining?
It does not fracture, behaves in a plastic manner
