Minerals Flashcards
What is an element?
A substance made up of only one type of atom
What are 8 elements and their abundance in the Earth’s crust?
Oxygen - 47%
Silicon - 28%
Aluminium - 8%
Iron - 5%
Calcium - 4%
Sodium - 3%
Potassium - 3%
Magnesium - 2%
Other elements - <1.5%
What is a mineral?
The things that rocks are made up of. A substance made of different elements
What are 5 rules a substance must follow to be considered a mineral?
- Must be solid at normal Earth conditions
- Must be naturally occurring
- Must be inorganic
- Must have a fixed chemical formula
- Must have specifically arranged atoms
What are minerals formed from?
Minerals form from molten material
What determines the size of crystals?
Cooling rate.
Slow cooling = larger crystals
Fast cooling = smaller crystals
Is glass a mineral, and why?
No. Cooled so quickly that atoms do not have enough time to rearrange themselves - breaching rule 5 (specifically arranged atoms)
How is the size and shape of mineral crystals determined? (Not cooling rate)
Crystals grow from the centre outwards by adding faces. Crystals have a definite shape, and the angle between the faces always remains the same.
If a crystal forms in a void or cavity, it will have a well-defined shape. If a mineral crystal forms next to another, it will form a grain boundary, and the shape will look irregular
What is a rock?
An aggregate of one or more minerals
What is a “habit” when describing a crystal?
It’s shape
What are the 7 possible habits of a crystal?
Isometric, Hexagonal, tetragonal, orthorhombic, monoclinic, triclinic, trigonal
What are some examples of isometric crystals?
Garnet, Diamond, Gold
What are some examples of Hexagonal crystals?
Calcite, Apatite, Tourmaline
What are some examples of tetragonal crystals?
Apophyllite, Rutile, Zircon
What are some examples of orthorhombic crystals?
Olivine, Topaz, Cementite
What are some examples of monoclinic crystals?
Gypsum, Azurite, Orthoclase
What are some examples of triclinic crystals?
Kyanite, Rhodonite, Axinite
What are some examples of trigonal crystals?
Ruby, Agate, Tigers Eye
What does it mean identify a mineral’s colour?
Different minerals have different colours, but some minerals share the same colour. It is determined by the arrangement of atoms (light reflection)
What does it mean to identify a mineral’s streak?
Residue left by a mineral when scraped across a porcelain streak plate. Streak is the colour of a mineral when it is broken up or powdered (scraped). The test can only be done if the mineral is softer than porcelain
What does it mean to identify a mineral’s lustre?
How well a mineral reflects light. Words used to describe lustre include: metallic, Vitreous, silky, pearly.
Most rock-forming minerals are Vitreous
What does it mean to identify a mineral’s shape?
Different crystals have different shapes/Habits. This is determined by by the arrangement if atoms or crystal structure
What does it mean to identify a mineral’s cleavage?
Some momerals have cleavage plains, these are plains of weakness (e.g. biotite mica)
What does it mean to identify a mineral’s hardness?
Different crystal have differen5 hardness. Hardness is measured from 1-10 on ‘Moh’s hardness scale’(1 softest, 10 hardest)
What does it mean to identify a mineral’s desnity?
Different minerals have different densities. Amount of mass per unit volume (gcm-³)
What does it mean to identify a mineral’s reaction with acid?
Some minerals will react with acid. If a mineral reacts with acid, fizzing/bubbling will be observed. Carbonate minerals react with acid.
In geology - we use weak HCl acid (hydrochloric)
What are the 11 rock-forming minerals we learnt about (the big table)?
Quartz, orthoclase feldspar, plagioclase feldspar, biotite mica, muscovite mica, augite, hornblende, Olivine, Calcite, garnet, kyanite
What are the characteristics of quartz?
(Habit, colour, hardness, cleavage, lustre, density,and streak)
Trigonal
White/grey or transparent
Hardness - 7
Doesn’t have cleavage plain. It has a conchoidal fracture
It is vitreous
Density of 2.65gcm-³
Colourless streak
What are the characteristics of orthoclase feldspar?
(Habit, colour, hardness, cleavage, lustre, density,and streak)
Triclinic
Peach/pink
Hardness 6.5
2 cleavage please near 90°
It is vitreous
Density 2.7gcm-³
White streak
What are the characteristics of
Plagioclase feldspar?
(Habit, colour, hardness, cleavage, lustre, density,and streak)
Triclinic
White/grey or blue/grey
Hardness - 6
2 cleavage plains near 90°
Vitreous
2.7gcm-³
White streak
What are the characteristics of biotite mica?
(Habit, colour, hardness, cleavage, lustre, density,and streak)
Monoclinic Hexagonal
Black, dark brown
Hardness - 3
Perfect cleavage in one direction
Vitreous-pearly
3gcm-³
White/grey streak