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.

Minerals and rocks from GLGY311 Lab

A better images of minerals can be found here

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.

Beautiful example of dolomite habit.
Beautiful example of dolomite habit.

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

Sample Properties


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


Chromite (alt)

Chem: FeCr2O4
Hs: brown streak, metallic luster, black granular
Other: black under both xpl and ppl



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

Lick here
Lick here
Lick here

Hornblende(type of amp)

Chem: Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)2
Type: Double Chain / Insolcate
Structure: T-O-T structure
Comp. Anio: (Si4O11)6-
Si-to-O: 4 ; 11
Cry. sys: Monoclinic
Hd: 5.0 – 6.0
Hs: shiny black – underlaying green?
Col/pleo: green-brown/light-darker
Relief: high/positive
Cleve: brittle – 2@60/120
Twin: simple twins (sometimes)
Habit: bladed / fibrous
Ext: inclined (14-25)
Int. col: 2nd low – 3rd high?
Other: dark opaque rim

Under XPL.


Chem: KAlSi3O8
Type: Framework / Tectosilicate
Comp. Anio: SiO2
Si-to-O: 1;2
Cry: Monoclinic
Hd: 6
Col/pleo: perthitic texture in pink-white
Relief: very low/-ve
Clev: 2@90
Twin: tarten/carlsbad
Habit: tabular
Int. col: 1st – grey/white



Chem: (Fe,Mg)SiO4
Type: Orthosilicate / Nesosilicate
Comp. Anio: SiO44-
Si-to-O: 1 ; 4
Cry. sys: orthorhombic
Hd: 6.5 – 7
Hs: yellow-green/olive green
Col/pleo: colourless-olive green/none
Relief: high/positive
Cleve: none/irregular
Habit: granular
Ext. parallel to crystal faces
Int. col: 2nd – 4th
Other: rarely with quartz



Type: Single Chain / Inosilcate
TOT: T-O-T structure
Comp. An: (SiO3)2-
Si-O: 1 ; 3
Hd: 5.0 – 7
shiny black – dull
weathered black pale green – pink
Relief: moderate/+ve
Cleve: 2@90
Habit: thin lamellar tabular parallel
Int. Col.: 2nd – brown/yellow

thin section


Chem: (Ca,Na)AlSi3O8
Type: Framework / Tectosilicate
Comp. anio: SiO2
Si-to-O: 1 ; 2
Cry. sys: Triclinic
Hd: 6 – 6.5
Hs: grey – white
Col/pleo: clear/dirty
Relief: low/-ve
Cleve: 2@90
Twin: albite/carlsbad/zone
Habit: tabular
Int. col: 1st – grey/white
Other: zoning – Na rich rim / Ca rich core
NOTE zoning in the last petrographic image.

Taken under PPL.


Chem: SiO2
Type: Framework / Tectosilicate
Comp. Anio: SiO2
Si-to-O: 1 ; 2
Cry. sys: rhombohedral / trigonal
Hd: 7
Hs: many colours
Col/pleo: translucide clear/none
Relief: low/negative
Cleve: none/concoidal
Twin: none
Habit: massive/colmnar
Ext. wavy
Int. col: 1st – grey/white




Metamorphic/Sedimentary Minerals and Rocks

Sample Properties


Chem: Ca2(Mg,Fe)5Si8O22(OH)2
green under PPL



Chem: Al2SiO5
Orthosilicate / Nesosilicate
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
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…



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]
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



with mud interclasts


with interclasts of fragments



Chem: KAl3Si3O10(OH)2
Sheet / Phyllosilicate
T-O-T+c structure
Comp. An: (Si4O10)4-
2 ; 5
Hd: 2.5 / 4.0
Hs: silvery/white – colourless
Col/pleo: clear/none
Relief: moderate/+ve
Cleave: perfect cleavage
Twin: none
Habit:massive/platy parallel / pebbly 2nd – 3rd vitrous



The second image (XPL) shows with stylolites…


Fossils in Packstone

to be updated…



to be updated…



First two images are from an altered formation of the mineral in igneous rocks.

Chem: Al2SiO5
Hd: 7.5
Hs: white/yellow
Col/pleo: clear/none
Relief: moderate to high/+ve
Habit: cylindrical/fibrous
Int. col: 2nd – pink



Chem: (Fe,Mg,Zn)2Al9(Si,Al)4O20(OH)4
Type: Orthosilicate / Nesosilicate
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



white, brown…
colourless – none
silky, fibrous
2nd – bright
turquoise similar to sillimanite in handsample


Zebra Dolostone

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

To be updated…

List of Minerals Properties To Be Updated

Please read what PPL and XPL.

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

titanite pale brown – none v. high/ +ve


lawsonite mod. High relief


Staurolite: pleochroic (light -dark yellow), cruciform,+

Andalusite: 2 @ 90, inclusion of other minerals, high relief, cloudy in PPL.

Cordierite: blobby/blocky, low interference, other minerals inclusion. And/cord look like quartz.

Silimanite: hand elongated, white bladed, thin pleochroic (yellow-orange), second order, high relief.

Chlorite: green under PPL. Purple/brown under XPL.

Clinopyroxene: higher birefringence and non-parallel extinction.

Epidote: “stain glass” yellow-green-blue under XPL. hand s vitreous.

Glaucophane: blue amphibole found in blueschists.

Tremolite: white in PPL, found in calcitic rocks only.

Updated Geologic Time Scale

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.

Basic construction of a Mohr Circle

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.

Continue reading Basic construction of a Mohr Circle

Stereographic projection for structural analysis

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).

Steronet with a plane and its pole
Figure 1: Steronet with a plane and its pole. Note the bottom half of a sphere is used. Click to enlarge.

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.

Figure 2: Highlighted in green is the primitive. The blue arrows are pointing to two great circle. The orange arrows are pointing to two small circles.
Figure 2: Highlighted in green is the primitive. The blue arrows are pointing to two great circle. The orange arrows are pointing to two small circles. Click to enlarge.

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

Normal fault with the Net-slip displacement and horizontal vector.
Normal fault with the Net-slip displacement and horizontal vector.

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

Stereonet with Data
Plane A: 040/36, Plane B: 320/40, Pi-girdle to Plane A and B (line of best fit crossing points 1 and 2), the hinge at point 3

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…

Hand written sample
Hand written sample

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.

Updated: 23-April-2016