30+ Thin Section Photos That Will Develop Your Interest in Petrography

 A “thin section” of rock is a sample that is mounted to a microscope slide and cut so thin that you can see light through it. The process of creating a thin section is a blend of artistry, technology and science.  

The art of preparing thin sections has been critical to understanding the core samples that scientists are observing. Thin section samples allow scientists to observe minerals in rocks, their crystal structure and texture at a microscopic level.

Want to revise how do geologists study rock? Follow this link to see our blog on "Studying Rock".

In this blog, we're taking you into the journey of thin section photos that were captured and given by students and young professionals from Finland, Ireland, Denmark, Czech Republic and Plymouth (UK). 

Again our purpose is to encourage students and professionals' research by promoting "learning and scope" of Geology through our blogs. Help us to help others in learning and understanding geology. See this link that how you can contribute to Learning Geology.

Note: We are using following thin section photos by having permission from their owners. If you like to use these photos, leave us a message or email us here.

1. A beautiful heart shaped hornblende in XPL (cross polarized light) view.It is a thin section of basalt with some secondary mineralization in the vesicles. Plagioclase is present in the form of black and white matrix and large phenocryst (with some zoning). Alignment of plagioclase grains is indicative of the "flow" of magma.

Photo Credits: Astaley

2. Thin Section of a Biotite and Muscovite, XPL view 

Photo Courtesy: Laura

3. Thin Section of a Plagioclase (orthoclase) and Pyroxene, XPL 

Photo Courtesy: Laura

4. Eclogite in Thin Section, XPL

Photo Courtesy: Laura

 5. Cummulate Rock with Pyroxene and plagioclase, XPL

Photo Courtesy: Laura

6. Blueschist, XPL

Photo Courtesy: Laura

7. Agglomerate in a Thin Section, XPL view
       Agglomerates are pyroclastic igneous rocks that consist almost wholly of angular or rounded lava fragments of varying size and shape. Fragments are usually poorly sorted in a tuffaceous matrix, or appear in lithified volcanic ash. (Britannica.com)

Photo Courtesy: Laura

8. Thin Section of a Pigeonite and Olivine, XPL

Photo Courtesy: Laura

9. Olivine phenocryst in Basaltic Lapilli, XPL

Photo Courtesy: Laura

10. Thin Section of a Gabbro, XPL
Showing minerals; Pyroxene and Olivine, plagioclase and others. Learn more about Gabbro here.

Photo Courtesy: Laura

 11. Another beautiful thin section of a Gabbro, XPL

Photo Courtesy: Laura

12. Thin Section of a Greenschist, XPL

Photo Courtesy: Laura

13. Thin Section showing intrusion of rocks from magma chamber into country rocks, XPL

Photo Courtesy: Jack Lewis Donnelly

14. Thin Section of a Sillimanite - a mineral found in rocks formed by the metamorphism of a mudstone. (XPL view)

Photo Courtesy: Jack Lewis Donnelly

15. Microgeode in ultrabasic vulcanite (a rare copper telluride mineral), 30 µm thin section, PPL and XPL 

Photo Courtesy: Petr Hyks

Photo Courtesy: Petr Hyks

                                                              See original photo here

16. Muscovite & biotite (30 µm thin section, PPL and XPL)

Photo Courtesy: Petr Hyks

Photo Courtesy: Petr Hyks
Same photo in XPL view. See original photo here

17. Quartz and epidote (30 µm thin section, PPL and XPL)

Photo Courtesy: Petr Hyks

Photo Courtesy: Petr Hyks

                                                        See original here.

18. Olivine (30 µm thin section, PPL and XPL)

Photo Courtesy: Petr Hyks
See this photo here on Petr Hyks' website

19. Zircons in biotite (30 µm thin section, PPL views, showing extinction)

                                                                                         

                                                                                  

                          Photo Courtesy: Petr Hyks
                              See this photo here on Petr's website

20. Zircon in biotite (30 µm thin section, XPL)

Photo Courtesy: Petr Hyks
See this photo here on Petr's website

21. Kyanite surrounded by muscovite (30 µm thin section, PPL and XPL)

Photo Courtesy: Petr Hyks
See these photos on Petr's page here and here

22. Zircon crystal in chloritized biotite (30 µm thin section, PPL and XPL)

     

Photo Courtesy: Petr Hyks
See these photos on Petr's page  here and here

Petr Hyks is 21 year old geology student from Masaryk University in Brno (Czech Republic). He has uploaded 5000+ photos about geology, astronomy and meteorology on his Flickr page. Follow this link to visit his website. Thank you Petr for contributing to Learning Geology and helping others to learn geology through your thin section photos. 🙂 Now following 10 thin section photos are from a geology student of University of Helsinki, Finland.

23. Thin Section of Olivine Diabase in XPL and PPL view.

Photo Courtesy: GeoAmethyst

24. Thin Section of Basalt in XPL view
        Having minerals: Olivine (in center) plagioclase, pyroxene and other accessory minerals

Photo Courtesy: GeoAmethyst

25. Thin Section of a Trachyte, XPL view

    Trachyte is an igneous volcanic rock with aphanitic to porphyritic texture. It is volcanic equivalent of Syenite. Major or essential minerals are alkali feldspar with less amount of plagioclase, quartz or feldspathiod. 

Photo Courtesy: GeoAmethyst

26. Thin Section of a Harzburgite, XPL view
      Harzburgite is an ultramafic igneous rock. It chiefly contains plagioclase (under 10%) , olivine, orthopyroxene (enstatite), clinopyroxene (diopside) and biotite. There could be a small amount of talc, carbonate, tremolite, cummingtonite, chlorite, serpentine and titanite.

Photo Courtesy: GeoAmethyst

27.  Another thin section of Harzburgite, XPL view

Photo Courtesy: GeoAmethyst

28.  Thin Section of Pyroxenite (an ultramafic igneous rock), XPL view

Photo Courtesy: GeoAmethyst

29. Thin Section of Trachyte showing Sandine mineral in center, XPL view

Photo Courtesy: GeoAmethyst

 30.  Thin Section of Andesite, XPL view
       It is an extrusive igneous, of intermediate composition, with aphanitic to porphyritic texture.              Here this thin section is showing chiefly hornblende and plagioclase.

Photo Courtesy: GeoAmethyst

31. Thin Section of Alkali Basalt (silica undersaturated) in XPL view.

Photo Courtesy: GeoAmethyst

32. Thin Section showing small clinopyroxene grains within orthopyroxene

Photo Courtesy: GeoAmethyst

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Useful Websites: 

1. Polarized light Microscopy (Image Gallery)
2. How to make a thin section
3. Petrographic thin section preparation
4. Guide to Thin Section Microscopy
5. Index of Minerals in Thin Section
6. Optical Petrography website by an Italian Geologist
7. Carbonate Thin Section Images and Exercises

Igneous Origin of Diamonds

Diamonds are a rare occurrence on the surface of the planet because it takes extremely hot and high pressure conditions to create them. Physical and chemical conditions where diamonds form only exist in the mantle, nearly 70 miles down or more. In that environment in the upper mantle, diamonds may be a common mineral! It takes incredible events, nothing that has ever been witnessed in historic times, to bring diamonds to the surface.

Kimberlite-Diamond-mantle-rock

Diamond deposits around the world (that have any economic significance) are associated with volcanic features called diatremes.  A diatreme is a long, vertical pipe formed when gas-filled magma forces its way through the crust to explosively erupt at the surface. Kimberlite a special kind of intrusive igneous rock associated with some diatremes that sometimes contain diamonds, typical coarse grained an bluish in color.    

Diamond-bearing kimberlite pipes are diatremes that originate in the mantle.

    Diamonds are xenoliths carried up from deep sources in the mantle, and often occur in association with other gem minerals including garnet, spinel and diopside. Most "economically significant" diamond deposits occur in ancient rocks (Precambrian age), but have been discovered on all continents. Because diamonds are so hard, they survive torturously-long histories, recycled through sedimentary and metamorphic environments without being destroyed. As a result they have been found almost everywhere as very rare, isolated discoveries. Diamonds of microscopic size have been discovered in meteorites and asteroid impact sites, and some metamorphic rocks. They are most extensively mined from kimberlite pipes or from alluvial gravels derived downstream from diamond source areas. It should be noted that most diamonds are not of gem quality, but those that are not are used for industrial purposes.

Credits to Phil Stoffer at geologycafe.com
Text and figures are used with permission.