Category Archives: Earth Science

Also known as Geology, Geosciences, etc. It is a science that deal with Geologic materials and processes which made them. A multidisciplinary field in which also includes Geophysics, Hydrology, Structure and Civil Engineering and many more.

Interference Figures

Introduction

Interference figures or some text may refer to as optical figures are used by mineralogists and other scientists to describe optical properties of crystals. In Geology, optical properties of naturally occurring crystals are used to identify and classify minerals. In addition some companies are interested in manufacturing economically valuable minerals such as synthetic diamonds have a growing interest on the behaviors of these figures.

The interference figures are produced when the polarized light is “split” by a crystal as a result of its physical and chemical properties. However, most textbook will refer to these properties as optical properties. Remember optical properties are caused by physical and chemical variations within the mineral. To obtain an interference figure, the mineral must be anisotropic (as opposed to isotropic).

A petrographic microscope (polarizing transmitting light microscope) must be setup the following way to obtain an interference figure:

1) Focus on a grain under Medium power objective lens on the center of the cross hair.
2) Switch the objective lens to High power (40X and up).
3) Flip the Condenser lens to the path of the light ray.
4) Insert/flip the Polarize to the path of the light that traveled through the mineral.
5) Insert the Bertrand lens and focus it (or remove the ocular lens).
6) Use the Accessory plate to determine the sign (+/-) of the figure. The measurements of vibration is always depend on the slow direction of the Accessory plate.

Uniaxial Minerals

The light will be slip into two components; epsilon (ε) and omega (ω). Following is an example of such image obtained using a microscope. Only one Optic Axis hence, the angle of which the isogyres (bands of extinction – black lines) form is 90-degrees.

Uniaxial Centered Optic
Uniaxial Centered Optic

The following is the same crystal when the Accessory Plate is inserted. Since the upper right has a blue isochrome (colour curves), it is clearly a positive mineral. But take a note that while the diagrams in textbooks may indicate strong blue and yellow regions with clear separations between them, it is just a representation of the following image.

Uniaxial Centered Optic Figure (positive)
Uniaxial Centered Optic Figure (positive)

Uniaxial Negative Figures

The value of component ε less than the value of component ω. Hence, will produce a negative interference figure.

Uniaxial Negative Ellipsoid of Revolution
Figure 1: Uniaxial Negative Ellipsoid of Revolution

Scenario A – If you are looking down at the Optic Axis (A on Figure 1 – above), in which the mineral is cut perpendicular to the Optic Axis, then a Centered Optic Axis interference figure (Figure 2 – below) can be obtained. In uniaxial we can only measure the O – vibration direction.

Interference Figure Diagram for Uniaxial Negative Centered Optic Axis
Figure 2: Interference Figure Diagram for Uniaxial Negative Centered Optic Axis

Scenario B – This is a situation where you are looking down the crystal in between the two vibration directions, but further away from the omega (ω). With each rotation of the stage, the interference figure will move around the field of view.

Interference Figure Diagram for Uniaxial Negative Uncentered Optic Axis
Figure 3: Interference Figure Diagram for Uniaxial Negative Uncentered Optic Axis

Scenario C – When a mineral is cut parallel to the optic axis, you will be looking down at C axis. This will produce a Flash figure. It is not very useful for Interference Figure analysis, but this type of figure is best used for determining birefringence.

Uniaxial Positive Figures

The value of component ε greater than the value of component ω. Hence, will produce a positive interference figure.

Uniaxial Positive Ellipsoid of Revolution
Figure 4: Uniaxial Positive Ellipsoid of Revolution

Scenario A – Bxa interference figure

Interference Figure Diagram for Uniaxial Positive Centered Optic Axis
Figure 5: Interference Figure Diagram for Uniaxial Positive Centered Optic Axis

Scenario B – Optic Axis interference figure

Interference Figure Diagram for Uniaxial Positive Centered Optic Axis
Figure 6: Interference Figure Diagram for Uniaxial Positive Centered Optic Axis

Biaxial Minerals

Biaxial Negative Figures

Biaxial Negative Ellipsoid of Revolution
Figure 7: Biaxial Negative Ellipsoid of Revolution

Scenario A – Between the 2-Optic Axises. Figure 8 below. This is a special Interference Figure known as Acute Bisectrix Figure (Bxa).

Interference Figure Diagram for Biaxial Bxa
Figure 8: Interference Figure Diagram for Biaxial Bxa Negative

Scenario B – Optic Axis based interference figure.

Interference Figure Diagram for Optic Axis Negative
Interference Figure Diagram for Optic Axis Negative

Scenario D – This will results in a Flash figure. Useful for determining birefringence, but not helpful in obtaining an interference figure.

Biaxial Positive Figures

Biaxial Positive Ellipsoid of Revolution
Biaxial Positive Ellipsoid of Revolution

Scenario A – Between the 2-Optic Axises. Figure X below. This is a special Interference Figure known as Acute Bisectrix Figure (Bxa).

Interference Figure Diagram for Biaxial Bxa Positive
Interference Figure Diagram for Biaxial Bxa Positive

Scenario B – Optic Axis interference figure.

Interference Figure Diagram for Optic Axis Positive
Interference Figure Diagram for Optic Axis Positive

Scenario D – This will results in a Flash figure. Useful for determining birefringence, but not helpful in obtaining an interference figure.

Evolutionary Family Trees in Paleobiology

Here are some family trees for Paleobiology University of Calgary laboratory samples. Based on class notes, lab notes, lab manual and my work notes. Refresh page if the current version does not appear immediately!

Also check out this HTML digital version with images at Paleobiological Hierarchy

Kingdom Animalia

Current version: 1.5

Kingdom Animalia
Kingdom Animalia (click on image to enlarge)

PDF file can be downloaded here.

Current version: 1.0

Kingdom Animalia for Lab 4
Kingdom Animalia for Lab 4 (click on image to enlarge)

PDF file can be downloaded here.

Current version: 1.0

Kingdom Animalia for Lab 5
Kingdom Animalia for Lab 5 (click on image to enlarge; VERY LARGE FILE!)

PDF file can be downloaded here.

Kingdom Protista

Current version: 1.0

Protista
Kingdom Protista (click on image to enlarge)

PDF file can be downloaded here.

Version Control

Same principles used for version controls in computer science and software engineering can be applied to any form of science. The diagrams above undergo controlled form of modification and “purification” in which each error is fixed by adding either 0.2 or 0.5 to the previous. In an event of a complete overhaul, the version number will be jumped to the next integer addition. This is great for rapid interval updates. Please send me the version number when you find an error. THANK YOU.

Refresh page if the current version does not appear immediately!

Microfossils

The information get updated on this page at rapid intervals. No guarantee is given on the accuracy of the published data.

SILICOFLAGELLATES

Hard parts: Skeleton
Composition: Opaline silica
Morphology: Apical & basal rings, Spines and bars, Rods are hollow
Symmetry: Bilateral
Habitat: Planktic
Stratigraphic range: L. Cretaceous – Holocene
Sediments: Silicoflagellithite
Movement: Passive (plankton)
Notes: none

DIATOMS

Hard parts: Frustule
Composition: Organic silica
Morphology: Epitheca and hypotheca, Connective band(epicingulum)
Symmetry: Radial or bilateral (sometimes altered)
Habitat: Planktic and Benthic
Stratigraphic range: Jurassic – Holocene
Sediments: Diatomite
Movement: Movement on short distances (active)
Notes: Symmetry axes (pervalar, apical,transapical) images/diagrams

COCCOLITHOPHORIDS

Hard parts: Coccosphere
Composition: Calcium carbonate
Morphology: Coccoliths
Symmetry: Mostly radial (rarely bilateral or pentameral)
Habitat: Planktic
Stratigraphic range: Jurassic – Holocene
Sediments: Chalks and calcareous oozes
Movement: Passive (plankton)
Notes: images/diagrams

TASMANITIDS

Hard parts: Test
Composition: ?
Morphology: Wall with large pores
Symmetry: Spherical or radial
Habitat: Planktic
Stratigraphic range: Cambrian – Miocene
Sediments: Oil shales
Movement: Passive (plankton)
Notes: none

FORAMINIFERA

Hard parts: Test
Composition: calcitic, aragonitic, organic, siliceous, agglutinated
Morphology: Wall with very small microscopic voids
Symmetry: ?
Habitat: ?
Stratigraphic range: ?
Sediments: ?
Movement: ?
Notes: unicelluar organism

RADIOLARIANS

Generally planktonic and dwells in upper water column. Like people high on weed, they just passively migrated through floating. Soft parts of the organism are often protected by complex skeletons. They are super duper small; 30 microns to 2 millimeters. May be found in colonies (like gangsters of the micro world) in deep water situations. A dude named, Hackle came up with the first classification for these known as Hackel’s Plates.

images/diagrams

Order ARCHEOSPICULARIA

Hard parts: spicules… also read notes
Composition: ?
Morphology:
Symmetry: Spherical but it becomes radial through evolution
Habitat: ?
Stratigraphic range: Middle Cambrian – Silurian ? Devonian
Sediments: ?
Movement: ?
Notes: Grow by adding each ring like section called sagital rings. The first ring is called cephalon, the second thorax and the rest is known as abdominal.

Order ALBAILLELLARIA

Hard parts: skeletons
Composition: ?
Morphology: skeletons with three intersecting bars
Symmetry: Bilateral
Habitat: ?
Stratigraphic range: ?Ordovician – Silurian throughout Permian – ?Early Triassic
Sediments: ?
Movement: ?
Notes: none

Order SPUMELLARIA

Hard parts: Test: porous capsule
Composition: ?
Morphology: Tangential: cortical, medulla and micro shells; Radial: principle and byspines
Symmetry: ellipsoidal, disc-shape, lenticular, latticed or spongy (spherical or radial ??-?-?-)
Habitat: ?
Stratigraphic range: Paleozoic – ?throughout Recent
Sediments: ?
Movement: ?
Notes: Solitary but sometimes (rare) colonial. Not to be confused with “sperm”…

Order NASSELLARIA

Architecture of Nassellaria
Architecture of Nassellaria

Refer to above image of Nassellaria;
A – Aperture; top/young
B – Cephalon
C – Thorax
D – Abdomen (Note all other additions comes AFTER thorax ring is classified as abdominal rings.)
E – Basal ring; bottom/adult

Mineralogy Media Library

Index:   B   |   C   |   E   |   F   |   G   |   H   |   K   |   M   |   O   |   P   |   Q   |   S   |   T   |   Z   |   Footnotes

Please ignore colours because they are inaccurate. Images should not be used for studying for exams. This is just a “fun” project and use it at your own risk! Please note that this is an supplementary add-on to the previous collection; Photomicrographs of Minerals.

Interference Colour Chart

Click here for computer generated chart: generate now
Birefringence Chart

C


Calcite


calcite_10-10calcite

Calcite Double Refraction


Double Refraction in Calcite

F


Fluorite


fluorite-1-PPL

H


Hornblende

The “Hornblende-xpl” image shows beautiful 56-124 degree cleavage.

Hornblende-xpl

K


Kyanite


Kyanite-PPLKyanite-XPL

P


Piemontite


Piemontite-1 PPL

Plagioclase


Plagioclase with Olivine inclusions - XPLPlagioclase with Olivine inclusions - XPL II

S


Sillimanite

The following images demonstrate the “addition” effect of colours as the accessory plate is inserted (images from left to right). This indicates a length-slow, or wave length addition.
sillimanite_423pplsillimanite_423xpl_1sillimanite_423xpl_2sillimanite_423xpl_3

Staurolite


Staurolite-PPLStaurolite-XPL

Z


Zircon


Zircon-PPL

Footnotes

You may also reference Photomicrographs of Minerals. To view the original larger image, Right click –> Open in a new tab/window. Redistribution or reproduction without prior permission is prohibited.

Classification of Fossils

Warning: This page is still being updated. Current material may be incomplete.

Introduction

We used specific scientific words to describe morphological features and other of organisms. Both the fossils and trace fossils can be analyzed in several different criteria. Special thanks goes to Kathleen Nester from the University of Calgary for helping me understand the morphological concepts.

Physical Characteristics

When Geologists, Paleontologists and fossil hunters search for fossils, they are heavily depend on the key identifiable physical characteristics of organisms. There is no such thing as a clear line between the difference between what is a fossil and what is not. Almost anything that is buried under the Earth can be considered as a fossil. However, the importance of the specimen to the Geologic time is very important. Let’s look at the physical descriptors.

After we established a sample is a true fossil, the next step is to determine its identity. There are several different methodologies in separating samples into Hierarchy of Life (K-P-C-O-G-S). Separation by physical characteristic is known as morphological division (or morphology).

Symmetry and Geometry (Gastropods, Ammonites and Brachiopods)

Symmetry and the shape (geometry) of fossils are determined by the organism’s DNA and the environment.

The best example of a complex natural symmetry is the starfish in the Class Asteroidea. It has a unique pentameral symmetry, which is not commonly found in other Groups, Classes or Genus. Therefore we can use this as an identifier for this type of fossil. There are other types such as radial symmetry, spherical symmetry and longitudinal symmetry to differentiate the variates of organisms into Classes and Genus.

W
D
T
S

Phylum Brachiopoda

Strophic shells have a true hinge line and may also have inter-areas; non-strophic shells have no true hinge line but may have palintropes(1). This is an external hinge structure. A strophic hinge line is straight while a non-strophic hinge line is curved(2).

Concavity is of a specimen can be obtained using external and or internal surface features. There are few descriptors we use; biconvex, convexo-concave, and concavo-convex based on the physical shape of the brachiopod shells. It is recommended to name the brachial valve first before naming the pedical valve. The pedical valve contains foramen(2).

Shell features such as also used for differentiation. Plicate literally means “folded” contains corrugations that go through the entire shell. Rugate are thickening of the shell in intervals, which radiates outwards in “circular” formation. Costate are also thickening intervals of the shell radiating directly opposite in “lines” formation(2).

Associated Time Frame

Geological Time Scale is somewhat subject to interpretation. There are several observations can be obtained in order to prove or disprove the boundaries of Epochs, Periods, Eras and Eons. If you “Google it”, you will come across several different versions of the Time Scale. A Geologic Time Scale with fossils superimposed can be found here. Please keep in mind that Science is always changing and the Geologic Time Scale has be adjusted almost in yearly basis as new evidence surface through research.

Not all organisms remains

Just because a time scale has a boundary at a certain age, it does not mean that the fossils appeared must also ceased to exist. In fact, there are more fossils that cut across divisions in the time scale than there are once bounded by them. The fossils or trace fossils that only appear within a certain division is usually known as an index fossil, because they can be used to identify (hence “index”) the time frame.

Association to Each Other

Based on where the fossils are found and the fossils around the one we interested in we can expand our understanding. For example, if a large fossil is surrounded by a relatively small fragmented bones type fossils, this may be an indication the large one is the predator and the small bones are from a prey.

Size doesn’t matter?

However, this is also subjected to great Scientific debate. Just because there are smaller bones of a different species it won’t necessarily means it is in fact the prey. Let’s look at a living example. Poisonous snakes are relatively smaller than human and while we do act as predators, it is also possible for snake to be the predator. In the future if someone finds a skeleton of a human with a snake imprint nearby, it would be wrong to assume the snake has killed the human. This is because human also have the capability to prey upon the sake. This is where we get into the muddy areas of Paleobiology and Paleontology.

Examples

Please read the Paleobiological Hierarchy page for detailed observational information.

References

1. http://geolmag.geoscienceworld.org/content/96/1/1.abstract

2. Kathleen Nester, University of Calgary (Undergraduate Student)