Salt Crystallizing in Water

[sjastro]

Another microscope image with a difference.

I decided to try my hand at cross polarization imaging.
Cross polarizing microscopes cost a few thousand dollars but the technology is ridiculously simple and only cost $40 to convert my stereo microscope into a cross polarizing microscope.

The cross polarizing unit was nothing more than clear glass filter taken from my ST-7XME and threaded to a Lumicon polarizing filter on both sides. One of the polarizing filters was rotated until most of the light reaching the camera was cut out. The sample itself sat inside the unit on the clear glass filter.

The left hand image was taken with normal light, the right hand cross polarized light. Each is five images stacked for maximum field depth.

Regards

Steven

[Larryp]

Fascinating images,Steven!

[multiweb]

That looks cool Steven. So what are we looking at. Salt dissolving in water or crystal forming after water evaporation? What kind of magnification is that? I also noticed there are little clusters of bright dots in the color shot. What are they?

[sjastro]

Thanks Marc,

The images are of crystals formed during the cooling process.
The magnification is difficult to define as it not only depends on the optics but also on the resolution of the image etc, but I would estimate it to be around 30X.
Both images are in colour, the normal (white) light image indicates more of a shadow effect as light is being blocked by the crystals reaching the detector. The image was processed to remove the colour cast associated with the tungsten filament lamp which probably gives it a monochrome look.

The cross polarized image is the result of having two polarizing filters orientated 90 degrees. Light entering the first filter is polarized (the light travels in a planar wave). The second filter at 90 degrees should according to classical physics block off the remaining light.
Classical physics however gets it completely wrong. Due to the quantum nature of light and the fact that blue light has the most energy in the visible part of the spectrum, some of the light passes through.
The blue parts of the image correspond to the least amount of light reaching the detector.
The reason why some areas transmit more light is that the salt crystals can cause the plane of the light wave to rotate before reaching the second polarizer. The blocking effect of the second polarizer is reduced due to this rotation.
The white dots represent maximum transmission.



Thanks Larry.

Regards

Steven

[AstralTraveller]

Planning a career in mineralogy?

[sjastro]

Ironic you should mention that since one of area of interest I have for cross polarization imaging is in the identification of meteorites.

Regards

Steven

[theodog]

Fine and very interesting images.
Well done!

[AstralTraveller]

Are you making the thin sections? Tedious job.

[sjastro]

Thanks Jeff.



I wouldn't consider doing the job myself.
There is a metallurgical lab where I used to work that would be able to assist.

In the meantime I will confine myself to taking pretty pictures of easy to prepare materials.:)

Regards

Steven

[AstralTraveller]

If you're ever in Wollongong drop by the Uni and visit Building 41 (The Science Building). In the foyer are about 1000 minerals and rocks on display, including a few meteorites. The latest display nearing completion is of the worlds oldest rocks from Greenland (3.7 - 3.85 billion years).

[sjastro]

Thanks that would be very interesting.

I read the the oldest rock found is from WA.

Regards

Steven

[AstralTraveller]

Not quite. The Jack Hill Formation contains the oldest dated minerals on Earth - zircons of about 4 billion years. The rocks themselves are alluvial deposits which have undergone several metamorphic events. So there was an igneous rock somewhere that was weathered and eroded. The zircons were washed into a sedimentary basin. The sediment was buried and lithified. Later it was folded and metamorphised several times. Despite all this the zircons remained a chemically closed system and so can be dated radiometrically.

What we have from Greenland are whole rocks which have remained unaltered for over 3.7 billion years.