Geology Exam 1 - Minerals & Igneous Rocks

Front 1

Mineral definition

Back 1

a naturally occurring inorganic solid with a specific chemical composition and a specific regular atomic architecture

Front 2

Halite cleavage and composition

Back 2

perfect in 3 directions, makes cubes.

Atomic structure looks like a cube.

Front 3

Graphite structure and bonds

Back 3

series of 2-D sheets stacked on each other.

Each sheet has strong carbon bonds, but between each sheet are very weak bonds.

Makes it easy to flake off.

Front 4

Diamond structure and bonds

Back 4

carbon atoms in diamond make a 3-D network of carbon tetrahedra (3-D triangles) sharing corners.

Every single bond is VERY strong

Hardest natural solid

Front 5

Why do some crystalline solids display external perfect shape of crystals whereas others have extremely irregular shapes?

Back 5

The shape can be determined by the other minerals crowded around it.

Front 6

What is the most important mineral group on Earth and why does this make sense?

Back 6

Silicates (90% of continental crust and higher in oceanic and mantle)

Made of 4 oxygen atoms around 1 silicon. Oxygen is ready to bond with many things.

Front 7

Silica Tetrahedron

Back 7

oxygen atoms define 4 corners of a 3-D object (tetrahedron). Each side is an equilateral triangle.

Front 8

Pluton

Back 8

when an irregular blob of magma freezes underground. Plutons are 10s of m to 10s of km across.

Front 9

Batholith

Back 9

intrusion of many plutons create a vast igneous body of 100s of km long and 100km wide

Front 10

Dikes

Back 10

a tabular (sheet-like) intrusion that CUTS ACROSS regional layering.

Show rifting (stretching)

Front 11

Sills

Back 11

tabular intrusions that run parallel to layering

Front 12

Which part of a volcanic system do plutons and batholiths represent?Which indicates a long lived subduction zone?

Back 12

Magma chambers (in fossil form).

Batholiths

Front 13

Do igneous rocks fall into distinct clusters based on chemical or mineralogical composition, or do they fall into a continuum?

Back 13

They fall into a continuous spectrum of compositions. Evolving compositions.

Front 14

Mafic vs. Felsic melting temperatures

Back 14

Mafic are dark and dominated by minerals that melt @ high temps.

Felsic are light and dominated by minerals that melt @ low temps.

Front 15

Why is there a range of crystallization temperatures?

Back 15

Variations in mineral and magma compositions and pressure experienced(depth).

Front 16

Geothermal Gradient (geotherm)

Back 16

The increase in temperature with depth in the Earth.

Slows after 100km.

Front 17

Is the mantle made of mafic or felsic minerals? Which rock dominates?

Back 17

Periodite is an ultramafic rock. (Green)

Front 18

What physically has to happen to a rock to produce decompression melting?

Back 18

Asthenosphere comes closer to surface. Rock rises.

Occurs at ocean spreading centers & continental rifts.

Front 19

Decompression melting definition

Back 19

occurs when rocks rise, pressure drops, and the solidus is crossed.

Front 20

What happens when water is added to hot, pressurized periodotite?

Back 20

It lowers the solidus of some of the minerals causing it to melt faster.

The water percolates upward between the mineral grains.

Front 21

Which types of boundaries cause decompression melting?

Back 21

Convergent and divergent.
Ridges and rifts.

Front 22

Which type of boundaries cause hydration melting?

Back 22

Convergent.
Subduction zones.

Front 23

Mantle Plumes

Back 23

Rising columns of hot rock below hot spot volcanoes. When it reaches lithosphere, the flow is deflected to sides.

caused by crystallization of iron in outer core. mantle gets hot enough to flow and sends up solid mantle.

150km below surface (litho.), partial melting produces volcanic magma.

Front 24

Color

Back 24

results from the way a mineral interacts w/ light. What we see represents the wavelength the mineral doesn't absorb.

Not reliable

Front 25

Streak

Back 25

color of the powder produced by pulverizing the mineral.

Fairly reliable

Front 26

Luster

Back 26

way a mineral surface scatters light.Compare it to a familiar substance.

ex:metal,silky,glassy,etc.

Front 27

Hardness

Back 27

measure of the relative ability of a mineral to resist scratching, and therefore represents the resistance of bonds from being broken.

Front 28

Cleavage

Back 28

when a mineral breaks to form distinct planar surfaces that have a specific orientation in relation the the crystal structure.

Front 29

Conchoidal fractures

Back 29

smoothly curving, clamshell shaped surfaces. Typical in quartz & glass.

Front 30

Compare mafic and intermediate/felsic lavas in terms of density and viscosity

Back 30

Mafic is denser but less viscous

Front 31

Viscosity

Back 31

resistance to flow

Front 32

Why do magmas rise?

Back 32

A rock expands as it melts, therefore it is less dense than the surrounding and it rises. Buoyancy

Front 33

What determines how far up a large blob of magma will rise?

Back 33

If magma is too dense it will rise until the density matches the surrounding rock.

Can become too viscous to force their way through fractures.

Front 34

Where does all partial melting start? What is the composition of this layer and the melts it produces?

Back 34

All melting starts in mantle.

A partial melt of an ultramafic mantle periodotite is a MAFIC melt that crystallizes to form a gabbro or basalt.

Front 35

What is heat transfer and assimilation?

Back 35

Mafic magmas cause heat transfer by directly melting felsic materals which then release water and stimulate more melting.

Assimilation is when original magma incorporates some felsic melt from heat transfer melting.

Front 36

How does Fractional crystallization work?

Back 36

As magma cools, minerals begin to crystallizae. Mafic settle first and remove themselves from the magma creating intermediate magma.

Front 37

Why does volcanism on continental crust produce many compositions, but ocean ridges produce only basalts?

Back 37

cont. crust is rich in felsic rock for assimilation