lab pt 2

Question 1

Carbonate Thin Section Textures

Answer 1

Sparite refers to crystalized calcite. It is usually .02-1 mm milky crystals that lack distinct internal structures. It is sub-euhedral and “jigsawed” together

Mud: This is microcrystaline calcite that is likely to precipitate due to algaes in calm enviroments.

Question 2

Ooids

Answer 2

These are concentric, small, carbonate grains with D< .25 mm. Modern ooids have a radial structure. They are mainly distinguished by size and shape.

An oolite is a rock made of ooids

Question 3

Peloids

Answer 3

These are grains of micro or cryptocrystalline calcite without internal structures

They tend to be silt to fine sand sized (.03-1mm) and are composed of pellets.

Question 4

Quartz in thin section

Answer 4

General: No Twinning, low relief

PPL: Clear to slightly murky, conchoidal fracture

XPL: 1st order grey, undulous extinction

Question 5

Volcanic Monocrystalline Quartz

Answer 5

This has all the properties of regular quartz but it will not have any inclusions

Question 6

Polycrystalline quartz

Answer 6

This appears as one crystal in PPL and many in XPL. It is usually eroded quartzite or sandstone grains.

Question 7

Chert

Answer 7

Appears as one crystal in PPL and in XPL it is a bunch of white and black dots

Question 8

Chalcedony

Answer 8

This is similar to overgrowths in PPL but is very fibrous in XPL/PPL

Question 9

Quartz Overgrowths

Answer 9

These are tough to ID because they are optically continuous in XPL but under close inspection there is a faint line of the original quartz grain

Question 10

Chert Cement

Answer 10

This will look like chert but between the grains.

Question 11

Feldspars

Answer 11

They generally twin, have 1st order grey birefringence, 2 directions of cleavage, moderate-high relief.

These can alter to clays that gives them a cloudy/muddy appearence.

Question 12

K-Spar

Answer 12

Orthoclase has simple twinning, perthitic textures of exsolved albite (tartan twinnnig), and is generally cloudier than plagioclase

Microline has tartan twinning

Sanidine has simple contact (Carlsbad) twins

Question 13

Plagioclase

Answer 13

Plagioclase has polysynthetic twinning. This looks like thin pinstripes that go extinct 180 degrees off from one another.

Question 14

Schist

Answer 14

This will have bright and dark sheets of mica

Question 15

Rhyolite and Basalt

Answer 15

This will be amorphous but includes euhedral plagioclase and sanidine

Question 16

Recycled quartzite

Question 17

Micas

Answer 17

Biotite: in PPL it is brown and pleochroic, it has low order interference colors also look for birds eye patterns

Muscovite: PPL it is clear to green and has BRIGHT interference

Question 18

Micrite

Answer 18

This is microcrystalline calcite that is brown/green in PPL and looks like mud

Question 19

Calcite

Answer 19

This is similar to quartz but will have rhombohedral cleavage, simple twins, lamallar twins, sub-hedral crystals, and bright blue interference.

Question 20

Aragonite

Answer 20

Overall it is very fibrous.

Secondary aragonite forms botroidal fans and primary aragonite forms seems or groundmass of acicular crystals.

Question 21

Dolomite

Answer 21

Variable relief in PPL with extremely high order interference in XPL. When a limestone is dolomitized it will have euhedral crystals.

It is also less likely to twin than calcite.

Question 22

Geopetal Structure

Answer 22

This refers to when shells are infilled with sparite and remnant sand grystals are at the base of the shell. It is important because it indicates stratigraphic up

Question 23

Pisoids

Answer 23

These are very similar to ooids but 2pisolites. They are larger, can be slightly oblong and are distinct from oncoids by not having a nucleating fossil and distinct from peloids by having concentric banding.

Question 24

Oncoids

Answer 24

These are large oblong shaped grains that have a nucleas > 2 mm. They look like roundish stromatilites and can even form around shells. They are best distinguished by finding a nucleating particle unlike ooids and pisoids that have a tiny round nucleas.

Question 25

Grapestones

Answer 25

This is when there is a oolite or pisolite intraclasts make another rock. They are distinguished in xpl by going extinct simultaneously even though composed of many small round grains.

Question 26

Forominiferans

Answer 26

These look like coiled chambers

Question 27

Corals

Answer 27

These will have slightly “tree-like” interiors. Look for radial symmetry to distinguish from other fossils.

Question 28

Bryozone

Answer 28

These are colonial organisms that form a fuzzy network that can be either elongated or radiating

Question 29

Echinoderums

Answer 29

These are sea urchin spines that go extinct as a singular grain and are “C” shaped. It also refers to any skeletal fragments that go extinct as a singular grain in xpl.

Question 30

Brachiopod fossils

Answer 30

These are like clams, the individual valves/shells may be seperated. Look for small tubular or collumnar edges to ID.

Question 31

Gastropod fossils

Answer 31

These are snail shells. In comparison to formineferans the are conical and foraminiferans are very circular.

Question 32

Plotting on a Ternary Diagram

Answer 32

1. ) Choose the axis you want to plot on (prefer upper two)
2. ) Choose the second axis you want to plot on (prefer base)
3. ) find the intercept on the line that is parallel to the second axis.
4. ) double check by going reverse

Question 33

Recycled Orogenic Sediments

Answer 33

These have a large abour of total Q and lithics but low feldspar. On the Qm diagram it is in the right edge, on the Qt diagram it is in the UR

Question 34

Arc Sediments

Answer 34

These fall in the bottom center of both diagrams. They have a large amount of lithics/spars and little quartz.

Question 35

Craton sediments

Answer 35

These are in the UL of the diagrams and have alot of quartz with very little lith and at most minor spar.

Question 36

Basement uplift sediments

Answer 36

These have a large amount of feldspar. They plot in the LL.