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.
The following images are taken from a Samsung S III phone (Yes, you can’t believe the quality of detail on these images came from a 8 pix camera; contact me for technical/electronics detail on that) during the lab periods for Geology 311 (Mineralogy and Rocks) Winter 2013 at the University of Calgary.
Please click on the image on the left to access the larger original file. Download the PDF Version here.
Igneous and Precipitate Minerals and Rocks
Chem: K(Fe,Mg)3AlSi3O10(OH)2 Type: Sheet / Phyllosiclicate Structure: T-O-T+c structure Comp. Anio: (Si4O10)4- Si-to-O: 2 ; 5 Cry. sys: Monoclinic Hd: 2.5 / 3.0 Hs: shiny black Col/pleo: tan/straw brown – dark brown or green – brown green Relief: moderate/+ve Cleve: perfect cleavage Twin: none Habit: massive/platy Ext: parallel / pebbly Int. col: 3rd – 4th Other: vitrous
Chem: CaCO3 Type: rhombohedral / trigonal Hd: 3 Hs: Colourless, white, grey colourless, maybe dirty Relief: high/positive Cleve: brittle / concoidal black with pastel stripes Twin: wiggly twins?!? Habit: crystalline/granular Ext: twinkling extinction Int. Col: VERY HIGH – 4th order Other: reacts readily with HCl
Chem: FeCr2O4 Hs: brown streak, metallic luster, black granular Other: black under both xpl and ppl
(Ca,Fe,Mg,Mn)3Al2Si3O12 Orthosilicate / Nesosilicate T-O structure Comp. An: SiO44- Si-to-O: 1 ; 4 Type: isometric / cubic Hd: 6.5 – 7 Hs: red but variety too Col/pleo: clear/dirty – none Relief: high/positive Twin: none/uneven Habit: blocky/cubic Ext: NA
Chem: Ca2(Mg,Fe)5Si8O22(OH)2 Inosilicate Monoclinic moderate/+ve green under PPL
Chem: Al2SiO5 Orthosilicate / Nesosilicate orthorhombic 7-7.5 red? Dark cross-like in x-section = chiasolite Col/pleo: clear/dirty – darker than Cordierite in ppl Relief: moderate/+ve Ext: parallel Int. Col: 1st – grey Other: looks like a dirtier Cordierite, higher relief LOW PRESSURE POLYMORPH
Bedding vs Cleavage
To be updated…
This rock is formed deep underground about ~15 to 30 km of depth with between ~200 to 500 degrees Celsius. Blue colour is caused by Glaucophane mineral in the rock, which is a type of amphibole.
Chem: SiO2 Hd: 7 Hs: black, grey, white Col/pleo: dirty brownish grains – none Relief: low/-ve Cleve: none/concoidal Habit: nodules Int. col: 1st – grey/white Notes: not a true mineral rather a siliceous ooze – fine crystalline in xpl. Hardness same as quartz
Chalcedony and cavity filled with quartz
Chalcedony is a type of fibrous cryptocrystalline to fine grained silica that forms in pores, cavities and vugs in pre-existing rocks by precipitation from Si-rich fluids that pass through the rocks. Agate is a more brightly coloured variety of chalcedony that typically shows colour banding, with the colours being due to trace amounts of iron and manganese (or, increasingly, to dyes!). The concentrically banded geodes that you see in rock shops are vugs that have been partially to wholly filled with chalcedony/agate.
Chem: (Mg,Fe)3(Si,Al)4O10(OH)2*(Mg,Fe)3(OH)6 Sheet / Phyllosillicate T-O-T structure Monoclinic Hd: 2-2.5 Hs: green clear – green Relief: high/positive Cleve: perfect cleavage foliated masses – 2nd – Berlin Blue Other: has inclusions
To be updated…
CaMg(CO3)2 rhombohedral / trigonal Hd: 3.5 – 4 Hs: Colourless, white, grey (due to impurities, it can be many colours) Col/pleo: colourless/none Relief: low-moderate Cleve: perfect Twin: black with pastel stripes, wiggly twins?!? Habit: crystalline/granular Ext: twinkling extinction Int. Col: VERY HIGH – 4th order Other: Sugary texture may only be observed in finely crystalline dolomite as opposed to curved crystals faces of coarse dolomite. HCL reaction is very poor to none. It is extremely difficult to separate dolomite from calcite using a thin section. Precipitate mineral!
Chem: FeAl2O-OH[Si2O7][SiO4] Sorosilicate Monoclinic 6 silver/pistachio green yellow or green colourless to greenish yellow Relif: high/+ve brittle – planar lamellar (not common) fibrous, coarse to fine granular, massive. 3rd – bright green vitrous, Notes: pearly (Regional and contact metamorphic rocks)
Garnet with pressure shadows
Please check the information for the mineral in the igneous table above.
Hematite (Ore) (B), Quartz (A)
On the XPL photo, you can see the radiating cement of quartz (A) and the think black-brown (to dark reddish) outline of hematite (B) Hs: red-brown streak, steel gray and metallic shiny
Chem: Al2SiO5 Type: Triclinic Hd: 5.5-7 Hs: blue Col/pleo: clear Relief: high/+ve Twin: simple twins (sometimes) Habit: bladed / tabular Ext: inclined Int. Col: 1st – grey/yellow Other: HIGH PRESSURE POLYMORPH, may show stepped appearance like “tree-bark” in thinsection
Chem: (Fe,Mg,Zn)2Al9(Si,Al)4O20(OH)4 Type: Orthosilicate / Nesosilicate Monoclinic Hd: 7-7.5 Hs: dark brown / black Col/pleo: honey/potato yellow – none (ppl) Relief: high/+ve Cleve: subconcoidal Ext: zoning? Habit: intersecting prisms like a cross Int. Col: 2nd – mid/high yellow Other: poikiloblastic (air bubbles), “stauros” greek for cross – 2intersecting prisms HEXAGONAL SHAPED EUHEDRAL
Monoclinic 5.0-6.0 white, brown… colourless – none moderate/+ve brittle 2@60/120 silky, fibrous 2nd – bright turquoise similar to sillimanite in handsample
This type of rocks were originally limestone, now transformed into ‘Zebra’ dolomite.
At least partially fracture controlled, because of planar zones of coarse, light-coloured dolomite in darker, fine grained host. However, all of the rock now consists of dolomite, including the dark fine grained portions, suggesting an earlier period of pervasive dolomitization.
Halite and Gypsum
Halite is a Precipitate! Since it is white in colour, hand samples may be contaminated with other minerals causing it to appear in different coulours. The Halite is pretty much table salt, but do not taste it.
Gypsum has a sugary texture, curved crystal surfaces
Clinopyroxene Ca(Fe,Mg)Si2O6 Single Chain / Inosilcate T-O-T structure (SiO3)2- 1 ; 3 Monoclinic 5.0 – 7 shiny black – dull weathered black earthy/brown – nonpleochroic moderate/+ve 2@90 sometimes carlsbad / zoning thin lamellar tabular inclined (35-48) 2nd – low/mid
Apatite Ca5(PO4)3(F,Cl,OH) – – – – Hexagonal 5 very small usually – never see clear/none high/positive none/concoidal none six sided euhedral – 1st – grey/white usually a captured/ looks standing up… looks like quartz but really small
Tourmaline Na(Fe,Mg)3Al6(BO3)3(Si6O18)(OH)4 Ring / Cyclosilicate – Si6O1812- 1 ; 3 rhombohedral / trigonal 7 black hexagonal prisms seen in class? variable – variable moderate/+ve none none striated prism parallel 1st – 2nd – moderate
Cordierite Al2SiO5 Ring / Cyclosilicate orthorhombic 7-7.5 clear/dirty – lighter than Andalusite, has border moderate/+ve subconcoidal sector twinning 1st – grey/white looks like a cleaner andalusite, has patchy domains that extinct at different angles within crystal, has sometimes brown outlined border around crystal
Glaucophane Double Chain / Insolcate Monoclinic 5.0 – 6.0 grey/lavender blue lavender blue to striking blue (ppl) bladed / fibrous 3rd – bright blue
Scale images are Copyrighted to The Geological Society of America. Please check their website at, http://geosociety.org. If you would like to add more “Facts” to this page, please contact me.
The following information is published for fun and NOT for any scientific value. Please do not take any information on this page as a fact or a hypothesis. This page is created base on some funny ideas going around in Geology.
Quaternary glaciation (last ice age): resulted in Sid, Diego and their friends Zeke, Carl and others became friends with a human child.
Rise of human civilization; gave birth to modern day self-centered idiots who destroy the Earth.
For the first time aliens from the planet LV-426 probe a human female for biological experiments.
Biological break though in human evolution was found when a man with one nut, known as A. Hitler, was discovered when his party came to power in Germany.
Strong evidence suggesting our great grand parents were monkeys who butt-%#^$k came to life. The epidemic HIV/AIDS has been attributed to modern human-monkey interactions in the wild.
Due to lack of water to reduce friction during sex, dinosaurs went extinct (Cretaceous).
Break up of Pangaea(Jurassic) into Gondwana and Laurasia since they can’t resolve their three-way relationship problems anymore.
For the first time, large trees and shrubs were grown.
Opium and marijuana(Cannabis) became very popular among the micro-organisms causing “ya-man” disease.
Carbonated drinks during this period have lead to major teeth problems among mammal population. The acid in their coke have dissolved their teeth during Carboniferous period.
Landmasses fall in love creating the new marriage, Pangaea. It won’t last very long since each other have accused of cheating from the very beginning.
Moon was formed as result of aliens attacking the Earth with nukes. One of the nuke bombs hit the Earth so hard, creating the basin near Mexico.
Earth was sexy hot during this time; too bad with age, she became what she is today.
All Engineering and Geology students should be able to understand and construct of Mohr Circles or Mohr diagrams by hand. Most companies use computer software to draw Mohr circles. However, it is important as a scientist for you to be able to do them manually. Indeed manual drawings are very useful in field work environments where you may have limited access to more sophisticated technologies. This is a guide was written specifically for the University of Calgary structural geology classes. However, the general scientific ideas behind Mohr circles will remain the same regardless of the application. I tried to make this article as simple as possible, so the general users can also benefit from it.
The stereographic projection is a methodology used in structural geology and engineering to analyze orientation of lines and planes with respect to each other. The stereonets is a type of standardized mapping system that allows us to represent various angles in 3D space on a 1D paper. They are used for analysis of various field data such as bedding attitudes, planes, hinge lines and numerous other structures. This is a very useful tool because it can reduce the workload by avoiding lengthy calculations.
In structural geology, we use the bottom half or hemisphere of the spherical projection. If you are a mineralogist, you will use the top half of the spherical projection for crystallographic analysis. The reasoning behind which hemisphere we used is more conceptual than anything. This will be explained in depth in a different article. What is important to someone who just started using steronets is to recognize that steronets represents half a sphere where the cross section has 360-degrees. The pole to the plane (“dip pole”) is at 90-degrees to the plane. Planes are lines are drawn on steronets as they intersect at the bottom of the sphere (Figure 1).
Types of Steronets
There are two widely used types (and may be more) of stereonets by structural geologists. They are equal area stereonet and equal angle stereonets. The choice either should not affect the data analysis. The analysis and interpretation of data achieved through the use of either equal area of equal angle steronets should result in same conclusions.
However, the equal area steronets will reduce the area distortion. In other words, it is often used to analyze accuracy of data from several different regions of the same area. It is also useful in structure stereonet contouring. Hence, most educational institutions prefer equal area steronets for their students over the equal angle stereonets.
The equal angle stereonets are suitable for kinematic analysis. In other words, they provide the best projection for analyzing the direction and the vectors of structural forces. This is because the equal angle stereonets preserves the true relationships between stratigraphic and structural features.
For our discussion here, I will be using Wulff-Lambert type, which will preserve the angles.
North:It is the true North which is denoted by the azimuthal angle of 000-degrees on the primitive. All strike angles are measured with respect to the true North.
Primitive: It is the outer most circle is the primitive. It is at 90-degrees from the center of the stereonet. Primitive circle is also a great circle but, it contains N, E, S and W directions at 000, 090, 180 and 270 degrees intervals.
Great circle: A circle on the surface of the sphere made by the intersection with the spehere of a plane that passes through the center of the sphere. The great circles run North-South (longitudinal) or up-down and bisect the sphere precisely. The great circle is divided in to 360 degrees (like 360 degree protractor) because maps are designed based on same azimuthal (bearing) directional vectors. If you have understand how 3D vectors work, this should be a no-brainer.
Small circle: A circle on the surface of a sphere made by the intersections of a plane that does not pass through the center of the sphere. Small circles run left-right (latitudinal) on the stereonets and are perpendicular to the great circles.
Types of Geological Plotting and Data Usage
– Bedding surface, fault or a structure (“features”): strike of any of these will plot as a line on the stereonet.
strike measured using the great circle
always rotate the tick mark for the strike to the North, then counts from East (right hand side) towards the center for dip (or use the right hand rule)
use same principles for overturned beds (you cannot differentiate an overturned bed from a regular bed on a steronet)
– Pole to a feature: is always exactly 90-degrees opposite to the dip direction of the feature.
should me marked as a dot with a circle around it
– Trend: tread is always taken on line to a plane (NOT on the line)
usually deal with folds axis or a fault (ONLY on intersection of the line)
move the intersection to the North (or to a straight line) and make a tick/line on the great circle where the intersection meets
move back the trace paper to align with North; the point at which the tick intersect the great circle is the trend
– Plunge: it provides the angular information on how deep a structure is dipping in to a surface; very common feature in coal beds and folds
plunge is the distance between the great circle and the intersection
– Rake (pitch): distance between the intersection and the great circle along a plane/line (must be less than 90) rake is the angle between strike and trend
On the animation above, I drew two vectors out of several which can be used to interpret a normal fault. The red arrow is the displacement vector which is obtained by the horizontal and vertical displacement. The horizontal displacement is indicated with the brown arrow (vertical displacement is NOT shown). The rake of the fault is between the left most edge of the footwall and the displacement vector(red). The green arrow represents the rate of drop with respect to the original block. We use slickensides to interpret the sense of motion in the field.
Example with Data
Based on the above diagram…
-There are two planes; A and B
-There are two rake angles measured on the planes itself; measured between the intersection point 3 and the great circle. For example, from intersection point 3 upwards towards NW direction of the great circle intersection of plane A. Plane B rake is downwards towards SE direction.
-The pi-gridle is determined by plotting poles to the Plain A and B at 90 degrees, then alining them on one of the lines on the stereonet. The point 1 and 2 are best fit line points for the poles that lies about the center of the diagram.
-Trend is the along the point 1 and 3, directly outwards on to the great circle (it is NOT marked in this diagram). It is measured on the great circle itself.
-Plunge is the distance between the great circle-trend intersection and the point 3.
A detailed diagram…
Manual versus Software
There are absolutely no differences between the interpretations made using manual drawing and software-based drawing of datasets. In work environment, we usually use software to generate stereonets. The software often eliminates many user errors, produce much better quality steronets extremely detailed analysis of datasets and make it easier to share with other over electronic devices. For someone who is starting in geology or structural geology, it is highly recommended to use paper and pencil over software. This will help you learn the fundamentals of stereographic projection. Typically university geology and engineering students are expected create stereonets by hand.