Petrology Media Library

The information posted here is not in a particular order. If you want to find something specific on this page, I suggest using page text finder on your computer (Ctrl + F). Important terms and information are in bold. For additional photographs and information, please visit the following pages:
Mineralogy Media Library
Photomicrographs of Minerals
Sedimentary Petrology Media Library

Igneous Petrology

Aphanetic verses Phaneritic Textures

In hand sample, aphanetic describes rocks with very fine grained minerals (hard to see with naked eye). Phaneritic is the opposite of that. In thin section, predominately small crystal size in a sample is described as aphanetic. The image posted under Plutonic versus Volcanic is a good example of Aphanetic (plutonic) verses Phaneritic(volcanic).

Competitive Growth

This is characterized by the wavy boundaries between two or more grains.

Competitive Growth - 10x XPL (~2mm across) Competitive Growth - XPL

Compositional Zoning

As the mineral grows, the chemical composition of the magma in the immediate vicinity evolved. This may cause a variation in chemistry in each layer of addition to the forming mineral. This is most commonly observed in plagioclase feldspars. In plagioclase, concentric bands around the crystal that undergo extinction (XPL) at various angles indicate such zoning. Normal zoning will have albite-rich rim and anorthite-rich core. Reverse zoning will have the opposite. By using an electron microscope or an electron probe, you may determine if it is normal or reverse zoning. Zoning is a type of disequilibrium texture.

Plagioclase Zoning - 4x (xpl) Plagioclase Zoning - XPL


It is a type of Chloritization where mafic minerals are converted to chlorite.

Cumulaus Textures

These textures are caused by accumulation of crystals due to gravitational settling (crystal segregation) in a magma chamber.

Cumulaus are the crystals that formed very early. They are usually well formed and euhedral. In “normal” magmatic conditions, one could expect the cumulaus minerals to be upper minerals in Bowen’s Reaction Series (Olivine, Pyroxenes, etc, etc).

Intercumulaus describes the minerals that formed in between the already formed cumulaus grains. Since the space is limited, these crystals often have subhedral to anhedral shape. SOme grains may even have formed with unusual shapes due to limited availability of components and space.

The following image is a near perfect example of cumulate and intercumulate minerals. The Chromite formed first and then Muscovite formed in between.

Chromite (cumulaus); Muscovite (intercumulaus)-PPL

An example of plagioclase as the cumulaus alongside clinopyroxene as the intercumulus.

Plagioclase (Cumulus); Clinopyroxene (intercumulus)-2X-xpl Plagioclase (Cumulus); Clinopyroxene (intercumulus)-4X-xpl

An example of Enstatite as the cumulaus with clinopyroxene(cpx) and plagioclase as intercumulus minerals.

Enstatite (Cumulus) Cpx & Plagioclase (Intercumulus)-4x-xpl


Info to be updated… Note that the plagioclase (“background”) in the following image is in extinction.

Heteradcumulus - XPL

Also research on Orthocumulate and Adcumulate textures.

Cumulophyric Texture

Please read Glomeroporphyritic Texture

Deformation Twins

Occur on albite twining on plagioclase and on calcite. Deformation twins lack straight lamellar form, which is observed in normal twins. They are characterized by the wedge shaped or bent twins. About 3 mm across the image.

Plagioclase Deformation Twins (4x XPL)


Devitrification characterized by spherulites and perlitic cracks.

Devitrification - 10x PPL (2mm across) Devitrification - 10x XPL (2mm across)


The embayed texture is characterized by having “dips” or bay-like sections in the crystal as a result of resorption. This is a type of disequilibrium texture.

Embayment - 4x XPL (~5mm across) Embayment - 10x XPL (~2mm across)

Equigranular Texture

The sample has grains about the same size. Opposite term is ineuigranular. Also check the image for Cumulaus Textures.

Equigranular Texture-XPL  4x XPL (~5mm across)

Glomeroporphyritic Texture

Clusters of phenocrysts crystals involving one type of mineral. The term cumulophyric is used when there are more than one type of mineral in a cluster.

Glomeropheric Texture - PPL (~11mm across) Glomeropheric Texture - XPL (~11mm across)

Granophyric Texture

This texture is produced as a result of rapid undercooling of quartz and feldspars. The two minerals grow at the same rate at the same time (simultaneous growth). The process is usually triggered by loss of water/dehydration in a granitic melt. They do not form as single crystals but rather penetrate each other in an irregular branching like intergrowths. Under microscope (XPL), the quartz intergrowths will undergo extinct at the same time.

Granophyric texture - XPL Granophyric texture (also CPX in green) - XPL Granophyric texture close-up 40x - XPL

Interstitial Texture

The background of the phenocrysts are one large feldspar. Also related to Cumulaus Textures because “interstitial” is a descriptor/modifier.

Olivine, K-feldspar, Chrom-PPL Olivine, K-feldspar, Chrom-XPL

Inverted Pigeonite

Characteristic of magmas which underwent rapid cooling. Commonly formed in rocks with plutonic origin. Also known as herringbone exsolution. Note that the first two pictures may or may not be inverted pigeonite. However, they also have the exsolution features and could be a partial representation of it. The last image shows what we ideally called inverted pigenoite.

Inverted Pigeonite - XPL Inverted Pigeonite (1) - XPL Inverted Pigeonite (perfect) - XPL Inverted Pigeonite - 10x XPL (~2.0mm across) Inverted Pigeonite - XPL Inverted Pigeonite 2x - XPL

K-feldspar type Exsolution

Caused by limited chemical mixing in the magma. Most commonly seen in K-feldspar with respect to Na-rich verses K-rich chemical environments (also read prethite verses antiperthite in notes or textbook). It can also occur on plagioclase with Si-Al chemical environments. Also check images under Poikilitic Texture

Exsolution - XPL

Ophitic, Subophitic and Nesophitic textures

The term ophitic is used when large pyroxene grains enclose small, random plagioclase laths. The proportion of pyroxenes is much larger than that of plagioclase.

The term subophitic is used when larger plagioclase laths are partially enclosed by pyroxene grains. The volumetric proportion of plagioclase is higher than that of pyroxenes. The two images are examples of nesophitic texture. Images shows subophitic texture.

The term nesophitic is used when large plagioclase has smaller interstitial pyroxenes. The volumetric proportion of the plagioclase is higher.

Subophitic Texture - PPL Subophitic Texture - XPL Subophitic Texture - XPL

Plutonic versus Volcanic

On the following picture, the left one is a thin section from a plutonic rock and the right one is from a volcanic rock. The difference is in the groundmass and the crystal growth. Finer grained groundmass is indicative of volcanic rocks. Volcanic rocks usually have more ground massvolume (relative to the larger crystal volume). Well formed euhedral crystals are indicative of plutonic rocks and they usually have less groundmass volume. Both images have exact same resolution with about 2.8 mm across each Field of View (width).
Difference between plutonic and volcanic rocks.-XPL

Pilotaxitic Texture

Groundmass crystals are randomly oriented.

Pilotaxitic Texture - 4x (~5mm across)

Poikilitic Texture

This is a type of porphyritic texture in which a host phenocryst (known as oikocryst) contains one or more other mineral(s) inclusions. This is caused by magmas that underwent slow cooling (undercooling) first stage and later underwent rapid cooling. During the first stage, smaller crystals were formed. During the last stage, these smaller crystals will be included within the larger faster cooled crystal. The easiest poikilitic grains to identify under microscope have usually only one grain inclusion (picture below). You can also see the faint perthitic exsolution on both PPL and XPL images.

Poikilitic Texture and Perthitic Exsolution - PPL Poikilitic Texture and Perthitic Exsolution - XPL

Pseudomorph Texture

It is a type of replacement texture in which one or several minerals replaces another already formed mineral. The new replacement mineral(s) will maintain the size and shape of the original one.

Rapakivi Texture

It is an overgrowth of plagioclase minerals on alkali feldspar mineral. This texture is caused by epitaxial (heterogeneous) nucleation where new nuclei is formed on a per-existing crystal. In most cases, this can be easily recognizable in hand samples.

Rapakivi Texture (epitaxial nucleation)


It is a replacement process in which feldspars and/or feldspathoids by fine white micas. This is observed as a fined dust like (dotted) appearance on feldspars. This texture is caused by hydrothermal alteration.

Seritization of Feldspar - 4x (3mm-grain) - PPL Seritization of Feldspar - 4x (3mm-grain) - XPL

Skeletal Texture


Spinifex Texture

Usually easy to recognize in hand samples. They are sub-parallel to dendritic growth of olivine or clinopyroxene crystals in some quenched ultramafic rocks generated from lava flows.

Spinifex Texture on a Rock Spinifex Texture - 4x PPL (~5mm across) Spinifex Texture - 4x XPL (~5mm across)

Sieve Texture

The following image shows a mineral (olivine) that has been formed in two different chemical conditions. The larger euhedral crystal is the initial crystal. After most of the initial crystal has formed, the mineral has started to remelt producing a slightly different composition of olivine at the corners (top right and bottom left). This process is known as resorption. An electron microprobe may be used to analyze the the chemical differences between them. This is a type of disequilibrium texture.

Olivine - XPL (magma mix variation)

Trachyte Texture

Caused by alignment of minerals (usually the elongated minerals such as feldpars) due to flow. Found in aphanetic rocks and easy to observer in hand samples than thin sections.

Trachytic (Trachytordal) texture Trachytic (Trachytordal) mineral alignment - XPL Trachytic (Trachytordal) min. alignment indicated with arrow - XPL

Xenolith verses Xenocryst

Xenolith is an inclusion of country rock. Xenocryst is an inclusion of a foreign crystal that may or may not be from the country rock (eg. Olivine).

Metamorphic Petrology


First two pictures: a beautiful example of Andalusite “cross” in PPL and XPL.

Andalusite Cross - PPL Andalusite Cross -XPL

Andalusite - PPL Andalusite - XPL (extinct) Andalusite - XPL


Corona is a rim (or several successive rims=coronas) of one or several minerals surrounding another unstable mineral. These reaction rims are formed as a result of partial replacement of minerals at the grain boundary of the unstable mineral (middle). This is a solid state process.

Order of minerals for this particular example is; Olivine (center) – Orthopyroxene – Clinopyroxene – Hornblende- Spinel – Garnet – Plagioclase (outer most). This is the most common order of coronas(??).

Coronas - 2x PPL (~11 mm across) Coronas - 2x XPL (~11 mm across) Coronas - 4x PPL (~5mm across) Coronas - 4x XPL (~5mm across) Coronas - 2x PPL (~11 mm across) Coronas - 2x XPL (~11 mm across) Several coronas on a rock

Fabric Types

To be updated…

S and L type fabrics S and L type fabrics labeled

Grossular Garnet

Garnet is isotropic (remain extinct under XPL). However, grossular garnet will have zoning like layers within it.

Grossular Garnet - PPL Grossular Garnet - XPL


Fiber like appearance with blue-brown interference colours.

Jadeite blue colour - XPL Jadeite brown colour - XPL


Kyanite - PPL Kyanite - XPL

Kyanite in rock hand sample


The following two images shows Garnet as a porphyroblast. By definition, porphyroblast is a larger crystal grown within a finer grained groundmass.

Garnet porphyroblast with Muscovite, Plage, Quartz and Biotite - 4x PPL (~5mm across) Garnet porphyroblast with Muscovite, Plage, Quartz and Biotite - 4x XPL (~5mm across)


Fibrous like Wollastonite but bright interference colours than Wollastonite. Not to be confused with Wollastonite.

Tremolite - 2x XPL (~11 mm across)


Fibrous but lower interference colours than Tremolite. Not to be confused with Tremolite.

Wollastonite - 2x XPL (~11 mm across)

How to fix overclocking failed error

This is a well documented boot failure issue on most Asus motherboard. When the issue arise, the message, “Overclocking Failed! Please enter setup to re-configure your system.” will be displayed on start up before the system goes into boot sequence. So, how can you fix this?

A typical Overclocking Failed! error.
A typical Overclocking Failed! error.

What causes the problem?

The K-type processors from Intel can be safely overclocked. The manufacture Asus has several built-in functions on their motherboard that takes advantage of this Intel K-type processors. The motherboard has a program in BIOS to change the processor and RAM memory speed. If you have not manually overclocked the RAM or the processor before this error was displayed, then it is most likely caused by memory frequency issue.

The Intel CPU and the memory frequency is often changed during an overclocking process. It also may change during a boot-up or shutdown process. When either boot-up or shutdown processes does not go to completion due to power failure or other issues, then it may result in the frequency for CPU/RAM stuck in a higher than normal value.

Here is how you fix it

As instructed on the error screen, go to your BIOS setup (F2 or DEL at the start-up). The first option is obvious; press F5 (or find other means) to set all parameters in BIOS to Default. Now reboot and if that fails, then try the following.

1) Change the profile under “System Performance” to “Power Saving” profile.

Asus Main BIOS page (EZ Mode)
Asus Main BIOS page (EZ Mode)-Click on enlarge.

2) Go to “Advanced Mode” (select or F7-check above image) then select “Ai Tweaker” tab from the top.

Ai Tweaker tab under Advanced Mode
Ai Tweaker tab under Advanced Mode-Click on enlarge.

3) Change the system Level Up to “Auto”. Note: if “Auto” does not fix your problem, change the setting to the lowest level.

Target DRAM Speed and System Level Up selector.
Target DRAM Speed and System Level Up selector-Click on enlarge.

4) The Target DRAM Speed should read around 1600MHz (or lowest RAM speed possible).

5) Select “Boot” tab from the top and make sure the “Boot Option #1” under “Boot Options Properties” reads “Windows Boot…”.

Boot Option Properties --> Boot Option #1 = Windows Bo...
Boot Option Properties –> Boot Option #1 = Windows Bo…-Click on enlarge.

6) Now press “Exit” at the top and select “Save Changes & Reset”. Your system should boot up normally.

If this also failed to resolve the problem, you are not in danger of losing your computer. Go back to “Advanced Mode” and select “Advanced” tab from the top. Now change the Intel CPU variables until you find a solution. This is under CPU Configuration section. Try different combinations. I recommend disabling “Limit CPUID Maximum” and “Intel Visualization Technology”. That is what worked for my computer.

Advanced Intel CPU BIOS option
Advanced Intel CPU BIOS option–Click on enlarge.

Advanced Intel CPU BIOS options-CPU Configurations
Advanced Intel CPU BIOS options-CPU Configurations–Click on enlarge.

Please note that the above instructions are not Scientific nor approved by the manufactures. They are based on my personal experience. I have fixed few Asus computers with this issue by following the steps. There is no way I can guarantee that these steps will also work for your system. Use the information with caution.

Cloud computing: a blessing and a curse

Right after the DOT-COM bubble began to shrink, a new concept of computing called cloud computing gave hope to a dying breed. It boosted the profits of entirely Internet based companies like Dropbox Inc. and opened the market for new Internet based companies. The next big step for this technology is the “smart home” which also referred to as “connected home”.

Continue reading Cloud computing: a blessing and a curse

Documentary: Don’t Panic – The Truth About Population

Title: Don’t Panic – The Truth About Population – BBC
Producers: Dr. Hans Rosling and BBC This World
Type: Social Science and Statistics
Country: UK (Britain)
Year: 2013
Website: web


According to Dr. Rosling, Mozambique should mine and burn their coal as they wish instead of being poor due to the myth of “Global Warming is caused by the poor”. It’s the rich like us in first world who should cut down the power usage.

The world population growth is not a major problem according the new statistics. In fact, the population growth will level off soon with fewer children born to women even in developing countries. However, this lecturer is highly optimistic on his analysis and projections of world human population growth.

Very good documentary and finally one professor which I can agree with.

How to build a basic antenna

We use wireless devices to send and receive information without worrying about physical obstacles. In the old days, most consumer grade wireless devices such as mobile phones, routers and RC controllers came with large antennas. Today some manufactures decided to go with internal or built-in antennas. This is not always beneficial to the consumer. For example, if you have a weak signal in an area, it would be difficult to change the position of the antenna because; you do not know where is it in the casing and you may not be able to place the device in a position. The solution is to add a external antenna.

Antenna Theory

This is a very specialized area of engineering and physics. In fact, I do not think that I am qualified or educated enough to go into details on antenna theory. Likely, an experienced Engineer has posted all the details here. If you need extensive information on how antennas work, that is the best place to start.

For our purpose of building a home made antenna, we only need few details from basic physics. This is because I will introduce you to a basic antenna design.

Antenna Length

All radio equipments comes with details on specific frequencies in which the data is transmit. We can use that information to build a whip antenna (single wire). The length of the antenna itself (“the exposed wire”) depends on the frequency of the device. To calculate the length, we take the speed, c in which the wave propagate (travel) and divide that by the rated frequency of the particular device.

The formula for length (actually it is the wavelength) is, l = c/f and since most waves travels close to the speed of light in a vacuum, we can assume that c = 2.998 x 108m/s. Now we know two unknowns (frequency is taken from a published documentation of the device), we can calculate the required length. For example, if I were to build an external antenna to my Vera home automation controller with the f = 908 MHz, I would have to build an antenna that is about 33.02 cm in length. But generally we do not built at full wavelength. Instead, most antennas use either 1/2 or 1/4 of the wavelength. As long as the antenna length is within those multipliers, it will work fine.

Antenna length difference due to wavelength difference between 2.4 GHz vs 900 MHz
Antenna length difference due to wavelength difference between 2.4 GHz vs 900 MHz

If you hate calculations, search for a online calculator. Make sure you are using the right calculator because depend on the type of antenna, the information is varies.

Build it

Once you have calculated the required length, you may use a piece of coaxial cable (with the copper core) to build your antenna. Strip the outer cable (ground plane) to expose the inner core copper wire. The length of the exposed core must be the exact same length as what we calculated for our antenna length. Let’s say we want a 908 MHz antenna. Then the core wire should be exposed exactly 33.02 cm or close to that. The length of the rest of the cable will not effect your wireless signals. But longer the cable, higher the impedance hence may even weaken the signal.

There are several choices on how to connect the other end to the device’s circuit board. I recommend against soldering directly onto to the PCB. Instead, use a pigtail connector or a wire. Some PCBs come with removable antenna wires (“clip ons”). They are usually U.fl connectors. Yes you can buy them online (cheap) with all the connectors and wires attached. If your board does not have removable connectors, you can solder a wire between the board and the pigtail connector. By keeping the antenna wire itself separate from the PCB, you now have greater flexibility in future modification.

If you do have removable connections between the PCB and the antenna wire, then it is most likely a U.fl type connector. Read more about other types of connectors here.

If you are building a GSM (~ 900 MHz) antenna, order something like, SMA female straight to U.fl/IPX Pigtail cable. The other option is to take the PCB connector from an old router (regardless of wifi frequency) and use a RP-SMA connector type antenna. Note that RP-SMA is the type that comes in 99% of all WiFi routers with external antennas. However, most GSM based antennas such as ~ 900 MHz requires a SMA female connector.

Most consumer products with antennas do not come with a good ground plane connection. You can connect a wire between the antenna lead and any of the socket plates (Example of a socket plate is highlighted by B on the following image) for a good ground connection. Make sure you clean the socket plates before attaching the ground wire.

Internal view of D-Link LAN Switch.
Internal view of D-Link LAN Switch.

Special note: if you are an electronics enthusiast in Calgary, try MRO for supplies. I am not affiliated with them nor promote them. However, I was able to find most electronics parts such as ICs, resistors, transistors, antenna parts, etc over there.