Petrology & meteorology through a microscope with thin rock sections

Campo del Cielo meteorite thin section – microscopy using Zeiss IM microscope (not using polarisation)

I have waited some considerable time for this meteorite thin section to arrive – from the famous Campo del Cielo fall. Largely iron (black areas), there are also some minerals.

The following photos are NOT polarised.

Andy

x4 objective:

x10 objective:

Ozona Texas meteorite thin section microscopy Leitz Laborlux 161117

Second light for the Leitz Laborlux 11 microscope today was to image my thin section microscopic slide of a meteorite fragment from Ozona, Texas. All images using Bresser MikrOkular camera – there is no polarisation in these images as the Laborlux 11 version I have does not have polarised filters.

The information supplied with the thin section states that the Ozona meteorite was found in Crockett County, Texas, USA, in 1929. There were several pieces weiging a total of 127.5kg. It is a classic H6 Chronite. My sample has come from the Michael Cottingham Meteorite Collection.

Andy

Information on chrondrites:

The following information on Chrondrite meteorites comes from Wikipedia. Chondrites are stony (non-metallic) meteorites that have not been modified due to melting or differentiation of the parent body. They are formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids. They are the most common type of meteorite that falls to Earth (around 85% of all meteorites). Their study provides important clues for understanding the origin and age of the Solar System, the synthesis of organic compounds, the origin of life or the presence of water on Earth. One of their characteristics is the presence of chondrules, which are round grains formed by distinct minerals, although the proportion of the meteorite that is composed of chrondrules varies considerably – they normally constitute between 20% and 80% of a chondrite by volume. Chondrites can be differentiated from iron meteorites due to their low iron and nickel content. Other non-metallic meteorites, achondrites, which lack chondrules, were formed more recently. Chondrites are divided into about 15 distinct groups on the basis of their mineralogy, bulk chemical composition, and oxygen isotope compositions. The various chondrite groups likely originated on separate asteroids or groups of related asteroids. Each chondrite group has a distinctive mixture of chondrules, refractory inclusions, matrix (dust), and other components and a characteristic grain size. Other ways of classifying chondrites include weathering and shock. Chondrites can also be categorized according to their petrologic type, which is the degree to which they were thermally metamorphosed or aqueously altered (they are assigned a number between 1 and 7). The chondrules in a chondrite that is assigned a “3” have not been altered. Larger numbers indicate an increase in thermal metamorphosis up to a maximum of 7, where the chondrules have been destroyed. Numbers lower than 3 are given to chondrites whose chondrules have been changed by the presence of water, down to 1, where the chondrules have been obliterated by this alteration.

The information from Wikipedia above there places the Ozona meteorite (as a classic H6 Chrondrite) in the category of Ordinary Chrondrites. Being H6, the chrondrules are less distinct than in some other meteorite thin sections in my collection.

Some features you may wish to look out for in my pictures below are variations in colour in the mineral content, orientation of mineral crystals in same direction (seen particularly in one of the high magnification images), very dense opaque material between the mineralised areas (?iron), areas with larger and others with small mineral crystals, and the shapes of the crystals in the high magnification images.

x4 objective:

x10 objective:

x40 objective:

Microscopy of Garnet Stone from Scotland

The following photos are microscopic images using Zeiss IM microscope of Garnet Paragneiss (Precambrian) from Loch Duich (Glenelg Inlier), Scotland.

This slide was obtained with number others from ebay second hand.

Information on Garnet from Wikipedia:

Properties: Garnet species are found in many colors including red, orange, yellow, green, purple, brown, blue, black, pink, and colorless, with reddish shades most common.

A sample showing the deep red color garnet can exhibit. Garnet species’ light transmission properties can range from the gemstone-quality transparent specimens to the opaque varieties used for industrial purposes as abrasives. The mineral’s luster is categorized as vitreous (glass-like) or resinous (amber-like).

Crystal structure: Garnets are nesosilicates having the general formula X3Y2(Si O4)3. The X site is usually occupied by divalent cations (Ca, Mg, Fe, Mn)2+ and the Y site by trivalent cations (Al, Fe, Cr)3+ in an octahedral/tetrahedral framework with [SiO4]4− occupying the tetrahedra. Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit. (Note: the word “trapezohedron” as used here and in most mineral texts refers to the shape called a Deltoidal icositetrahedron in solid geometry.) They crystallize in the cubic system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show cleavage, so when they fracture under stress, sharp irregular pieces are formed (conchoidal).

Hardness: Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this mineral group shows a range of hardness on the Mohs scale of about 6.5 to 7.5. The harder species like almandine are often used for abrasive purposes.

Magnetics used in garnet series identification: For gem identification purposes, a pick-up response to a strong neodymium magnet separates garnet from all other natural transparent gemstones commonly used in the jewelry trade. Magnetic susceptibility measurements in conjunction with refractive index can be used to distinguish garnet species and varieties, and determine the composition of garnets in terms of percentages of end-member species within an individual gem.

I tried a neodycromium magnet on the slide and it did not appear ot be magnetically attracted – but then I do not know what proportion of this rock is garnet (possibly just the crystals within the matrix) and it is thin, both of which might explain the failure for magnetic attraction.

Andy

x4 objective:

 

x10 objective:

x32 objective:

First light: Bresser Mikrocam 9.0 on Zeiss IM microscope

I have found out today why this high resolution microscopic camera was so cheap on Astroboot! It only has drivers for Windows XP and Vista – and do what I may I could not get them to work on Windows 7. Therefore, to get it working, I have had to pull out an old Windows XP laptop (from the Ark!) and it does work with this – sometimes you need to hang onto these things and not upgrade everything. It has now become the Bresser Mikrocam computer but does make the camera somewhat bulkier to carry around.

First light images are quite reasonable although some dust I will need to remove later. Initially, I did not work out how to change the white balance so the marble images below all have a blue colouration whereas (once I found the white balance correction button in the software) the Teschenite pictures are far better.

Both marble and Teschenite are from Scotland – 30 micron thin microscopic sections.

Andy

Bresser-Mikrocam-9-0-image-Croc-Mor-Marble-221017-x4.bmp (below):

Bresser-Mikrocam-9-0-image-Croc-Mor-Marble-221017-x10.bmp (below):

Bresser-Mikrocam-9-0-image-Croc-Mor-Marble-221017-x32.bmp (below):

Bresser-Mikrocam-9-0-image-Croc-Mor-Marble-221017-x40.bmp (below):

Bresser-Mikrocam-9-0-image-Lugar-Ayrshire-Teschenite-221017×4.bmp (below):

 

Microscopy of microfossils and rock formations from Scarborough

These slides were purchased from SDFossils on ebay Sept 2017.

They compose of a five slide set of thin sections – one is of shelly limestone showing fossils. The others show rock structure – including oolites which look for all the world like fossils but aren’t!

All photos on Zeiss IM microscope with Bresser MikrOkular camera. For this post only x4 and x20 objectives were used.

 

Shelly Limestone

Shelly Limestone x4 objective – microfossils are seen within the stone

For comparison purposes the following photo is from the Museum of Wales, showing fossils within limestone:

Oolites

Oolite or oölite (egg stone) is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Ancient Greek word ??? for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm; rocks composed of ooids larger than 2 mm are called pisolites. The term oolith can refer to oolite or individual ooids. Some exemplar oolitic limestone, a common term for an oolite, was formed in England during the Jurassic period, and forms the Cotswold Hills, the Isle of Portland, with its famous Portland Stone, and part of the North Yorkshire Moors. A particular type, Bath Stone, gives the buildings of the World Heritage City of Bath their distinctive appearance (Wikipedia).

x4 objective:

Laminated sandstone & mudstone

The following are photographs of microscopy of two laminated rock sections (sandstone and mudstone) from Scarborough.

In geology, lamination is a small scale sequence of fine layers (so called laminae) that occurs in sedimentary rocks. Laminations are normally smaller and less pronounced than bedding. Lamination is often regarded as planar structures one centimetre or less in thickness, whereas bedding layers are greater than one centimetre. However, structures from several millimetres to many centimetres have been described as laminae. A single sedimentary rock can have both laminae and beds. Lamination consists of small differences in the type of sediment that occur throughout the rock. They are caused by cyclic changes in the supply of sediment. These changes can occur in grain size, clay percentage, microfossil content, organic material content or mineral content and often result in pronounced differences in colour between the laminae. Weathering can make the differences even more clear. Lamination can occur as parallel structures (parallel lamination) or in different sets that make an angle with each other (cross-lamination). It can occur in many different types of sedimentary rock, from coarse sandstone to fine shales, mudstones or in evaporites. Lamination is a fine structure and hence it is easily destroyed by bioturbation (the activity of burrowing organisms) shortly after deposition. Lamination therefore survives better under anoxic circumstances, or when the sedimentation rate was high and the sediment was buried before bioturbation could occur. Lamination develops in fine grained sediment when fine grained particles settle, which can only happen in quiet water. Examples of sedimentary environments are deep marine (at the seafloor) or lacustrine (at the bottom of a lake), or mudflats, where the tide creates cyclic differences in sediment supply. Laminations formed in glaciolacustrine environments (in glacier lakes) are a special case. They are called varves. Quaternary varves are used in stratigraphy and palaeoclimatology to reconstruct climate changes during the last few hundred thousand years. Lamination in sandstone is often formed in a coastal environment, where wave energy causes a separation between grains of different sizes (Wikipedia).

Laminated sandstone x4 objective:

Laminated sandstone x20 objective:

Laminated mudstone x4 objective:

Permian floodplain deposit 260817 with LOMO MNC-1 polarising microscope

I have included three photos using the Bresser MikrOkular camera below from my thin section of Permian floodplain deposit viewed using my LOMO MNC-1 polarising microscope. I can’t see any obvious fossils. Possible fossils from such floodplains were described in an article by Simon et al in the Journal of Sedimentary Research, http://jsedres.geoscienceworld.org/content/86/8/944.

A map of the world in the Permian is not as we would think of it today – a large single continent:

My slide comes from Dona Ana County in New Mexico – its location in the USA and the county map is shown below, together with the area’s stratigraphy:

Andy

 

Permian-floodplain-deposit-260817-0-6x-intermed-lens.bmp (below):

Permian-floodplain-deposit-260817-4x-intermed-lens.bmp (below):

Permian-floodplain-deposit-260817- 7x-intermed-lens.bmp (below):

Crossed-polar illumination rock samples using dedicated Leningrad Optical-Mechanical (LOMO) Stereo Polarizing Microscope (MNC-1)- Transmitted & Reflected Light 16/7/2017

At the RAG meeting in June 2017, I demonstrated plain polar illumination of thin rock sections on a biological microscope modified for polar illumination by myself. The pictures were impressive. Since that time, I have added posts in which I have attempted, with some success, to do crossed polar illumination on that microscope – the Zeiss IM inverted biological microscope.

It is amazing what comes up on ebay – my latest acquisition is an example of the Leningrad Optical-Mechanical (LOMO) Stereo Polarizing Microscope (MNC-1)- Transmitted & Reflected Light. This old and dirty example has seen much use, is highly scratched, but was a good (cheap) price and comes with rotating stage, and a professional setup for both transillumination and epi-illumination in plain and crossed polarised light.

It turns out that the difference having a scope designed for this task masks is quite significant – or so my experience tonight would suggest – as you can see below.

Andy

Leningrad Optical-Mechanical (LOMO) Stereo Polarizing Microscope (MNC-1):

The oculars on this scope are larger in diameter than those on the Zeiss IM/IM35 – but thankfully the Bresser MikrOkular camera comes with an appropriate adapter!

The first two photos I am going to show demonstrate the view through the microscope without any slide. The polarising filter between the stage and illuminator is set to 90 degrees difference between the two pictures. This demonstrates that when this polariser is at 90 degrees to the one between the eyepiece (ocular) and slide then the two polarising filters are said to be crossed and no light gets through (the image is black):

Leaving the microscope polarising filters at the settings for the second slide above (ie crossed polarisation so no light gets through), I inserted a slide of Glauconitic sandstone from Upper Green, Folkestone, Kent, UK. This microscope has oculars (2 choices of magnification), an intermediate lens of varying magnifying power, and a fixed objective (as yet I don’t know the power of this).

The Glauconitic sandstone with x1 intermediate magnifiying lens gave following view:

The picture above demonstrates birefringence in some of the crystals. Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive) (https://en.wikipedia.org/wiki/Birefringence). Crystals in the sample refract the light and change its polarisation phase as they do so – so that some of the light is no longer crossed at 90 degrees polarisation and becomes visible. The amount and nature of this change is typical of different crystals and can be used to identify them.

The following comes from https://en.wikipedia.org/wiki/Glauconite:The following comes from https://en.wikipedia.org/wiki/Glauconite:

Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color with very low weathering resistance and very friable. It crystallizes with a monoclinic geometry. Its name is derived from the Greek glaucos (γλαυκος) meaning ‘blue’, referring to the common blue-green color of the mineral; its sheen (mica glimmer) and blue-green color presumably relating to the sea’s surface. Its color ranges from olive green, black green to bluish green, and yellowish on exposed surfaces due to oxidation. In the Mohs scale it has hardness of 2. The relative specific gravity range is 2.4 – 2.95. It is normally found in dark green rounded brittle pellets, and with the dimension of a sand grain size. It can be confused with chlorite (also of green color) or with a clay mineral. Glauconite has the chemical formula – (K,Na,Ca)1.2-2.0(Fe+3,Al,Fe+2,Mg)4(Si7-7.6Al1-0.4)020(OH)2.nH2O. Glauconite particles are one of the main components of greensand and glauconitic sandstone, and glauconite has been called a marl in an old and broad sense of that word. Thus references to “greensand marl” sometimes refer specifically to glauconite. The Glauconitic Marl formation is named after it, and there is a Glauconitic Sandstone formation in the Mannville Group of Western Canada.

 

Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles, especially with polarized light (https://en.wikipedia.org/wiki/Pleochroism). In the table above, the peochromatic characteristics of glauconate are that it appears yellow-green, green, deeper yellow, bluish green.

In the photo below, I have increased the magnification of the intermediate lens to 4x and this now shows clearly crystals with all the colours mentioned above:

Rotating the stage is supposed to lead to colour changes in the birefringence so I gave that a try tonight – did not seem to make much difference as you can see below. One of the adjustment screws on the stage is bent limiting how far it can be turned in one direction so I can’t properly centralise the specimen so it rotates around one spot – this means I had to use X and Y controls on stage to keep recentring it each time I rotated the stage – need to get that sorted.

Images showing effects of rotating stage on berefingemence of Glauconitic sandstone, Folkestone (below):

I now changed the sample to Ritland Impactite & some other samples. The following images are all crossed polarised images using the LOMO MNC-1 with 2x intermediate lens.

Ritland Impactite (below) – notice new colours that are not present in the sample above:

Chondrule-rich unclassified NWA meteorite found in Sahara desert 2016 (below) – 2x intermediate lens – thickness of this sample meant it was difficult to get focus at higher magnification:

You probably are wondering the same thing as I did at this point – can I do anything similar with rocks from my own backyard? Thin sections are very expensive to produce – need expensive machinery anyway which I don’t have. The LOMO MNC-1 does have the capacity to use reflected light and I also have a HL150-AY cold light source with swan-light attachments – currenltly no polarised filters on the latter but it can help with reflected light non-polarised images.

So, I popped outside and picked up a relatively flat small stone from the garden path…….it is about 2.5cm longx2cm wide (below):

LOMO-MNC-1-Rock-from-garden-path-0-8x-intermed-lens-160717.bmp (below, this series of images feels a bit like those seen as Rosetta closed on Comet 67P!): The following image is taken using reflected light WITHOUT polarisation:

LOMO-MNC-1-Rock-from-garden-path-2x-intermed-lens-160717I.bmp (below): The following image is taken using reflected light WITHOUT polarisation:

LOMO-MNC-1-Rock-from-garden-path-2x-intermed-lens-160717II.bmp (below): The following image is taken using reflected light WITHOUT polarisation:

LOMO-MNC-1-Rock-from-garden-path-4x-intermed-lens-160717.bmp (below): The following image is taken using reflected light WITHOUT polarisation:

LOMO-MNC-1-Rock-from-garden-path-7x-intermed-lens-160717.bmp (below): The following image is taken using reflected light WITHOUT polarisation:

LOMO-MNC-1-Section-rock-from-garden-path-reflected-light-no-polarisation-160717field-X.bmp – first image below shows this field of view without polarisation, the second image using plain polarisation:

Non-polarised:

Plain polarised (same field as above):

When I attempted to view the above field using crossed polarised filters, nothing showed. In fact, throughout the sample there was very little berefringence seen in crossed polarisation – little but not nothing – here and there some showed. It was difficult to capture what was there due to limited sensitivity of the Bresser MikrOkular camera.

The following is one attempt to photograph birefringement with crossed polarised filters on this rock, on a different field of view from that above and using x0.6 intermediate lens.

The first picture is with plain polarised light and the second with crossed polarised light:

Plain polarised light:

Crossed polarised light, on same field of view as above – birefringence is there if you look carefully but it is very faint:

Modifying Zeiss IM biological microscope for cross polarisation of minerals

Cross polarisation involves placing linear polarised filters, one before slide and one afterwards.

I achieved this using £3.95 polarisation film and second hand linear polarised filter from ebay, some old lollipop sticks, superglue, glue gun and some elastic bands!

Andy