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Flashcards in lab pt 2 Deck (37)
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1
Q

Carbonate Thin Section Textures

A

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.

2
Q

Ooids

A

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

3
Q

Peloids

A

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.

4
Q

Quartz in thin section

A

General: No Twinning, low relief

PPL: Clear to slightly murky, conchoidal fracture

XPL: 1st order grey, undulous extinction

5
Q

Volcanic Monocrystalline Quartz

A

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

6
Q

Polycrystalline quartz

A

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

7
Q

Chert

A

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

8
Q

Chalcedony

A

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

9
Q

Quartz Overgrowths

A

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

10
Q

Chert Cement

A

This will look like chert but between the grains.

11
Q

Feldspars

A

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.

12
Q

K-Spar

A

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

13
Q

Plagioclase

A

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

14
Q

Schist

A

This will have bright and dark sheets of mica

15
Q

Rhyolite and Basalt

A

This will be amorphous but includes euhedral plagioclase and sanidine

16
Q

Recycled quartzite

A
17
Q

Micas

A

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

18
Q

Micrite

A

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

19
Q

Calcite

A

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

20
Q

Aragonite

A

Overall it is very fibrous.

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

21
Q

Dolomite

A

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.

22
Q

Geopetal Structure

A

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

23
Q

Pisoids

A

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.

24
Q

Oncoids

A

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.

25
Q

Grapestones

A

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.

26
Q

Forominiferans

A

These look like coiled chambers

27
Q

Corals

A

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

28
Q

Bryozone

A

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

29
Q

Echinoderums

A

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.

30
Q

Brachiopod fossils

A

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

31
Q

Gastropod fossils

A

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

32
Q

Plotting on a Ternary Diagram

A
  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
33
Q

Recycled Orogenic Sediments

A

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

34
Q

Arc Sediments

A

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

35
Q

Craton sediments

A

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

36
Q

Basement uplift sediments

A

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

37
Q
A