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Geotechnics > Rock Types > Flashcards

Rock Types Flashcards

1
Q

What is a mineral

A

A natural, inorganic substance which has a definite chemical composition and arranged atomic structure

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2
Q

What is a rock

A

aggregates of one or more mineral. The properties of rock are determined by the minerals and the arrangement of said minerals relative to each other.

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3
Q

what is the origin of the 3 rock types

A

Igneous - crystallised from magma
sedimentary - erosional debris from other rocks
metamorphosis- rocks altered by heat and/or pressure

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4
Q

What environment are the 3 rock types found in

A

Igneous - underground or in lava flows
Sedimentary - deposition basins often underwater
metamorphosis - mostly deep inside mountain chains

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5
Q

What are the rock textures of the 3 rock types

A

Igneous - mosaic of interlocking crystals
sedimentary- mostly granular and cemented
metamorphosis - mosaic of interlocking crystals

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6
Q

What are the rock structures of the 3 rock types

A

Igneous - massive and structureless
sedimentary- bedded and layered
metamorphosis - crystals oriented due to pressure

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7
Q

What are the rock strengths of the 3 rock types

A

Igneous - very strong and uniform
sedimentary- low and can have planar weakness
metamorphosis - high variability and can have planar weakness

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8
Q

what are 3 major examples of each rock type

A

Igneous - basalt, granite, granodiorite
sedimentary- sandstone, limestone, clay
metamorphosis - gneiss, schist, slate

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9
Q

What is cleavage and what is fracture

A

Cleavage is a preferential split. It will break in a particular plane which will leave a perfectly flat surface. Rocks don’t have cleavage and will instead have fractures which is a lack of cleavage, resulting in a undulating surface when broken

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10
Q

What is the tenacity of a rock

A

The response of a rock on sudden impact - is it brittle or malleable

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11
Q

What are the two classes of rock forming minerals

A

silicate minerals and non silicate minerals (carbonates, oxides, halides, sulphides, sulphates and phosphates)

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12
Q

What are the main features and properties of the mica group

A

planar sheets arranged in layers so water can easily seep in to cause weathering. Has perfect cleavage parallel to the basal plane,

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13
Q

What happens in the weathering of mica

A

Metal ions are removed from the mineral and dissolved

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14
Q

What happens in the weathering of feldspar

A

Mineral reacts with water’s H+ ions. This requires flowing water to introduce new H+ ions

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15
Q

What are the columns of magma that rise through the earth’s crust and their horizontal counterpart

A

Dykes and sills

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16
Q

What are felsic and mafic igneous rocks

A

Felsic is acidic, meaning a higher silica content. Mafic is basic meaning higher metal oxide content

17
Q

Why do intrusive igneous rocks have larger grains than extrusive igneous rocks

A

Intrusive igneous rocks, those that are formed within the earth’s crust, cool down slower so the grains have time to grow large

18
Q

What is porphyritic and how does it occur

A

Large grains surrounded by smaller grains. Occurs when intrusive rocks are suddenly ejected while still cooling

19
Q

Why is quartz hardest to weather while olivine and pyroxene easiest to weather

A

quartz has the most complex structure and possesses more covalent bonds. Olivine and pyroxene have simpler structures with more ionic bonds

20
Q

What are anhedral and euhedral shapes and what causes them

A

euhedral means distinct shapes while anhedral is non distinct shapes. The minerals that solidify first tend to have euhedral shapes while those that solidify last have anhedral shapes as they are left with the remaining volume so don’t have the freedom of choosing their shape. Therefore, higher melting point (so solidifies earlier) means more euhedral

21
Q

What are the two types of sedimentary rock

A

Clastic (exogenic) and non clastic (endogenic)

22
Q

What determines [ ]of sedimentary rocks:
grain size
grain roundedness
sorting/ grading

A

grain size - energy of the deposition method. More energy means larger grains can be transported then deposited
grain roundedness - distance from mother rock. Further away means more weathering so more rounded
sorting/grading - variation in depositional events

23
Q

What is lithic/arkose/quartz arenite/graywacke sandstone

A

High in rock fragments, high in feldspar, pure quartz, high in matr

24
Q

what is lithification

A

The transformation of sediments such as sand, mud etc into rock through pressure and temperature. Mud becomes shale, sand becomes sandstone, gravel becomes conglomerate

25
Q

What is diagenesis

A

all the processes involved in transforming sediment into rocks. Includes compaction (the removal of water in between sediments) and cementation (involves ions precipitating to form new crystalline material between sedimentary grains)

26
Q

What is the dott classification

A

A classification of sandstone that classifies sandstone based on main constituent (quartz, feldspar etc) and matrix (the glue that holds the fragments together) percentage

27
Q

What is anisotropy and isotropy

A

Properties of a rock that signify heterogeneity and homogeneity in different directions. Anisotropic rocks could be stronger in certain directions for example while isotropic rocks will exhibit the same properties in all directions

28
Q

what is the difference between clastic and non clastic sedimentary rocks

A

Clastic sedimentary are formed when bits of other rocks are weathered and deposited. Non clastic rocks form from the evaporation of water or from remains of plants/animals.

29
Q

What happens to the grains in metamorphic rocks

A

due to heat and pressure, the minerals (the grains) shift and separate then recrystallise, leaving no void spaces

30
Q

What are the 3 types of metamorphic rock and what distinguishes them

A

thermal/contact (temperature), dynamic/dislocation(stress), regional(temperature + stress). Note dynamic occurs when two mountains move into each other at shallow depths

31
Q

What happens when more energy is applied to metamorphic rocks

A

They have increased crystal size (so are more shiny) and have more foliation (banding/layering)

32
Q

What causes foliation

A

Heat and pressure

33
Q

Why can’t granite become slate and mudstone become gneiss

A

Different rocks require different amounts of energy to metamorphize. Granite needs too much energy to metamorphize so can’t become slate, while mudstone will melt instead of metamorphize at the energy required to become gneiss

34
Q

What is marble a metamorphosis of

A

Limestone

35
Q

What are the three metamorphic rocks that clays, silts and volcanic ash can become in order of energy

A

slate, phyllite, schist

Geotechnics (4 decks)

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