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Geotechnics > Characterisation Of Minerals > Flashcards

Characterisation Of Minerals Flashcards

1
Q

Characterisation of minerals is done by which criterion?

A

Colour

Lustre

Form(shape,group,clustering)

Hardness(resistance to abrasion)

Cleavage(preferential split, only minerals have this, rocks have planar weaknesses)

Fracture(nature of broken surface)

Tenacity(malleable or brittle)

Specific gravity

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2
Q

What are the two main mineral classes?

A

Silicate (65%)
oxygen and silicon are chief rock forming minerals

Non-silicate(35%)
Carbonates,oxides,halides,sulphides,sulphates,phosphorites

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3
Q

The mica group belongs to which mineral type?

A

Silicate

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4
Q

Describe the mica group

A

Easily split into thin flakes due to perfect cleavage parallel to basal plane

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5
Q

Two types of mica?

A

Mascovite- colourless,silvery

Biotite-dark brown/black

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6
Q

Describe the feldspar group

A

Very common minerals found in the earth’s crust

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7
Q

2 types of feldspar?

A

Alkali feldspar

Plagioclase feldspar

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8
Q

The feldspar group also belongs to which mineral group?

A

Silicate

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9
Q

What are the six main silicate minerals?

A

Olivine
Pyroxene
Amphibole
Mica
Feldspar
Silica

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10
Q

Of the silicate minerals, which is the most susceptible to weathering?

A

In order: olivine, pyroxene, amphibole, Mica, Feldspar and Silica

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11
Q

How does Mica weather?

A

Complex reaction where metal ions are removed from mineral.

Reaction results in soluble ions and clay minerals.

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12
Q

How does Feldspar weather?

A

They weather via hydrolysis
As water is absorbed into the feldspar, kaolinite is often formed

The S in feldspar stands for hydrolysis

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13
Q

What is a dyke?

A

A sheet of rock formed in a fracture of a pre-existing rock through the rising of magma

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14
Q

What is a sill?

A

A sheet intrusion that has intruded between older layers of sedimentary rock or lava

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15
Q

What is the difference between intrusive and extrusive igneous rock?

A

Extrusive cools quickly above ground
Intrusive rocks cool quickly beneath ground

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16
Q

The silica content in rock varies from []-[]% ?

A

40-80%

17
Q

High silica rocks are [ ]

A

Felsic or acidic (silic-felsic)

18
Q

Low silica rocks/ metallic oxides are [ ]

A

Mafic/basic (mafICK, metallICK)

19
Q

What is the significance of an igneous rock being intrusive or extrusive?

A

Extrusive cools quickly, finer grains(no colour separation)

Intrusive cools slowly, larger grains

20
Q

What does it mean if your igneous rock has large minerals?

A

It had plenty of time to cool (intrusive)

21
Q

What are the two types of eruptions?

A

Fissure and central

22
Q

What is special about a fissure eruption?

A

They occur when a dike penetrates the surface.

Low viscosity flow, goes far (runny)

Fine grained Basaltic lava (fine balls)

23
Q

What is special about central eruptions? (Explosive, command centre go BOOM)

A

Ejection of lava, ashes and gas

24
Q

What is meant by pyroclastic?

A

Produced by volcanic ejections
Pyro - crazy
Clastic -fantastic!boom!
Crazy boom rock

25
Q

Igneous rocks can range from [] to []

A

Felsic to ultramafic

26
Q

The more mafic, the more []

A

Reactive

Mafic-mafia-excitable

27
Q

A more mafic igneous rock sits higher or lower in the silicate mineral reactivity scale?

A

Higher

Mafic -less silica content- more reactive

28
Q

What is meant by equigranular texture?

A

All crystals are of approximately the same size

29
Q

What is meant by inequigranular?

A

Some crystals are larger than others

30
Q

What is meant when a rock is porphyritic?

A

Large crystals surrounded by smaller ones

Porphyritic - poor - parasitic
Little ones flock to the big one

31
Q

What is meant by a Phaneritic rock texture?

A

A rock with large, clearly visible interlocking crystals

I’m a BIG “phan”

32
Q

What is meant by an aphantic rock texture?

A

Aphantic frantic hard to find

Too fine grained for mineral constituents to be identified

33
Q

What is significant about euhedral minerals in a rock?

A

Clearly defined edges, formed first and so got to have a defined shape

34
Q

What is significant about anhedral minerals in a rock?

A

Formed after the euhedral minerals

Have less defined edges

Geotechnics (8 decks)

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