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Olivine in Plane Polarized (left) and Cross Polarized (right) Light
The amount of olivine would seemingly make this a picrite.
physicsfun
Fluorescence and Birefringence in Calcite: two samples of calcite- each with different impurities that produce blue fluorescence for the small crystal and red fluorescence for the larger one under a 405nm violet laser. Also one can clearly see that the single laser beam takes two paths through the crystals- the speed of light in a calcite crystal depends on polarization because the refractive index is different depending on the polarization orientation of the light transmitted through it. ➡️ Follow the link in my profile for info on where to get this and other amazing items featured here on
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Green Laser through Optical Calcite
From Minas Gerais in Brazil comes this 4" wide specimen of optical calcite placed upon a reflective CD-R disc. A green laser beam is directed through the crystal in the direction shown by the arrow. Green laser light is scattered as it enters and exits the calcite. Within the calcite the laser beam stimulates red fluorescence likely due to manganese impurities.
The photo was taken through red laser goggles acting as a high Q magenta (green rejection) notch filter.
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I spend way too much time in geology labs photo taking, and not mineral identifying!
earthstory reblogged
February 8, 2019
The beauty of Igneous and Metamorphic Petrology. I don’t really like microscope work, but these thin sections make it a bit more enjoyable!
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Psychedelic amphiboles.
To study the composition of a rock a geologist first has to make a thin section, which is a thin slice of rock, about 0.03 mm thick mounted onto the glass. This makes a rock transparent to the light and minerals within the rock can be seen under the microscope. The crystal structure of the minerals alters the light, creating a vivid colour palette when rock is well-preserved.
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Geology is pretty
Thin section: small pieces of various rocks viewed under a microscope
Double Refraction This is a crystal of the mineral calcite, a mineral with an extremely high birefringence. Birefringence is a property of how some transparent materials interact with light. A birefringent crystal like calcite has one direction where light moves rapidly through the crystal and another direction where light moves more slowly. When a beam of light enters a crystal of calcite, it splits into 2 separate rays, each vibrating (or polarized) in a different direction. When light moves into a crystal from the air, it refracts or bends, and the path it takes depends on how fast it moves. In other words, light enters a crystal of calcite and splits into 2 different beams. The light coming in from behind this crystal started as a single beam, but as it entered the calcite it split into 2 separate rays, each taking a different path through the crystal. When the light exits the crystal to head towards your eyes, each ray exits at a different point, so the image that you see behind the crystal is duplicated when the light comes out. -JBB Image credit: https://flic.kr/p/22SFK4v Read more: http://bit.ly/2P1NIWO
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bryanseym Thin section of a garnet schist under cross-polarized light. Rocks are cool.
physicsfun Fluorescence and Birefringence in Calcite: two samples of calcite- each with different impurities that produce blue fluorescence for the small crystal and red fluorescence for the larger one under a 405nm violet laser. Also one can clearly see that the single laser beam takes two paths through the crystals- the speed of light in a calcite crystal depends on polarization because the refractive index is different depending on the polarization orientation of the light transmitted through it.
Lovely and colorful view of a schist in thin section
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chellaur-deactivated20181022
Adding the accessory plate to check change in interference colors
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I’m an igneous and metamorphic petrology kind of gal, but I when I looked down the microscope at this limestone I audibly gasped. These nebula-looking things are protists called foraminifera that have been replaced by calcite. The forams are identified by their chambered tests, which are preserved in the rock, showing the protist’s original shape.
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chellaur-deactivated20181022
Viking Compass
Vikings were known for their prowess in sailing and navigating large stretches of open water 1000 years ago. But how did they accomplish these feats of navigation before the widespread availability of magnetic compasses in Europe? Icelandic sagas detailing aspects of Viking life may hold a few clues. Some sagas mention the use of rocks, named sunstones to find the location of the Sun to navigate by. The property that would have enabled this handy feat is called polarization. You can think of these polarized crystals as having fast lanes and slow lanes for light. Just like in a congested traffic jam where you would want to be in the fastest lane to get to where you are going, light will preferentially follow the “fast lane” in the crystal, causing light to be directed in a particular orientation in the crystal. Researchers suggest that Icelandic Spar would be the most likely choice for a sunstone, it is a rock that would be familiar to the Vikings comprised of calcite, a mineral that is birefringent, meaning there are two “fast lanes” that light can travel through. How would this be used to find the Sun’s position? Well, if the crystal was positioned so that light from the sun was able to pass through a calcite crystal’s “fast lanes” equally, it would be the only orientation of the crystal where both beams of light present in the crystal were equally as bright, enabling the user to find where in the sky the sun is, even on a cloudy day!
Researchers led by Guy Ropars from the University of Rennes in France tested this concept out using a piece of Iceland spar recovered from a sunken British ship and found that they were able to find the location of the Sun within 1% of its true location. While this study reveals that is possible to find the Sun’s location using a sunstone, a Viking sunstone has not been found on any recovered Viking ships. Because of this, researchers do not know for sure if Vikings used sunstones to navigate in the past, but it is a possibility that would have helped them navigate before the widespread use of magnetic compasses in Europe!
-AND
Image Credit: https://flic.kr/p/9xh4ML -Photo by Mike Beauregard
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A little video i took last year of a calcite crystal under a cross polarised microscope. I believe the FOV is around 2mm in diameter.
Muscovite surrounded by quartz in a metamorphic rock