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Blue Halite Imagine sprinkling a little bit of this on your evening meal. This is the mineral halite – literally NaCl or common table salt. The Na and Cl atoms in table salt are arranged in an alternating pattern that builds up one of the classic simple cubic structures found in minerals.
Photogenic Fluorite Fluorite is the mineral that gives its name to the term “Fluorescence”, and these crystals of fluorite are fluorescing due to a UV lamp placed just outside the photo area. For a material to Fluoresce, it must be exposed to one type of electromagnetic radiation (light), absorb the energy from that light, and then give it back off as a different type of light.
Titanic Tanzanites!!
This is a photo of Saniniu Laizer, a small-scale miner who until last week worked in the mining district of northern Tanzania, the only place on the planet where the gemstone Tanzanite comes from. The stones he’s holding in his hand just changed his life; they are the largest tanzanites ever discovered by far. The largest known tanzanite stone before these weighed 3.3 kilograms; these weigh 5.8 and 9.2 kilograms. He sold them to the country’s mining ministry for the equivalent of $3.4 million US, and said he plans to build a school and a shopping center in his hometown with some of the money.
Double Rainbow Caldera This shot of double full rainbows was taken by Jasman Singh Mander after a storm and shared through the US Department of Interior’s feeds. The beginning of a rainbow occurs as sunlight enters a raindrop. As the light enters the water, the light slows down and is refracted, changing path to go towards the center of the bubble. However, not all refractions are the same. White light, as from the sun, contains all the colors mixed together, but when light bends, individual colors will separate, with violet light refracting the greatest and red light refracting the least. These rays of light then hit the far side of the water droplet and reflect back out of the front of the droplet, but in a slightly different direction from where they came in. Thus, the main rainbow comes from light being separated and reflected back, and it shows up when the sun, the water droplets, and your eyes form the correct angle.
One crystal, two colours, no magic...
The beauty of gems and crystals is an interaction between mind, mineral and light, and some minerals have structures that produce interesting optical effects, opal being an obvious example. The beautiful tanzanite crystal in the photo (see http://on.fb.me/1B8IMQyfor an intro to this purple wonder) is exhibiting another of these properties, which goes under the name of pleochroism, a word coming from the Greek for many colours. A pleochroic crystal actually appears different colours depending on the angle of viewing, and some gems have a very mild version, while others, including tanzanite, a somewhat more extreme one.
Crystals are regular arrangements of atoms in a symmetrical repeating lattice, and while the number of individual patterns atoms can order themselves into is almost infinite, all minerals crystallise in one of 6 (or 7 depending how you divide things) crystal systems, based on the length of the axes of their unit cell (the smallest 'chunk' of a mineral that can exist) and their angles of intersection. One system is regular and even, known as cubic or isotropic, with equal length axes meeting at right angles, the others exhibit ever greater degrees of wonkiness. This distortion is what allows the gem to play with light in this way and delight our eyes.
As light enters the crystal and encounters the lattice, it flows through it down different pathways following the axes, with the rays splitting into two or three. Some directions will be more densely packed with atoms than others, and the light will move at different speeds through them, and be absorbed differently. Since the colour that we see is what is left behind when the crystal has selectively absorbed some of the wavelengths of the light passing through it, different colours can result in the different rays, which then become apparent when the crystal is rotated, or, as in this case, when a change in growth direction occurred.
Each pathway through the lattice also polarises the light, forcing it to vibrate in a single direction, and this property is the basis of the gadget gemmologists use to see this phenomenon. Two chunks of Polaroid plastic, orientated at right angles to each other are set in a circle and used to look at the gem. Each half of the Polaroid will show one colour. The property is also useful for distinguishing minerals in thin sections, those slices of rock beloved of geologists.
Loz
Image credit: MIM Museum.
Chameleons are living LCD screens
There are animals that are able to change colour as needed, both for camouflage and communication, though the actual mechanism has so far proved elusive. Squid and octopi are two well known examples of marine invertebrates that do so, but amongst land animals none are more famous than this charming family of lizards (see videos in links at bottom). Recent research has finally teased out of reality the knowledge of how they change hue. We thought that we were pretty clever inventing LCD screens in which currents and magnetic fields rearrange crystals to produce moving images (or as a favourite author put it 'humans beings were so amazingly primitive that they still thought digital watches were a pretty cool idea'), but it turns out that, as in so many things, we were recreating something that the natural world had already evolved for itself.
We are all filled with crystals of many kinds, from the apatite crystals in our bones and teeth to the DNA in the nuclei of our cells, which exists there in a strange quasi crystalline mush. Remove the fluids and all the proteins in your body would crystallise. Indeed, we use many regular and ordered molecules in our bodies, from the chemicals that bind to your neuroreceptors to the carefully crafted shapes of our immune system's antibodies. The molecules are constructed to have very precise matches, so that only the right chemical shape will be able to bind to the receptor. This underlies the entire communication system of living beings, within each cell and in coordinating the different systems of our bodies.
Chameleons have two layers of skin cells one above the other filled with floating nanocrystals, evenly spaced throughout the cells in an arrangement not dissimilar to silica spheres in precious opals. Like opal spheres, the spacing between the crystals is similar to that the wavelengths of light, and they can control the spacing, and hence the colour that they wish to reflect in order to blend in with the background. These lizards also use their ability for communication and sexual display.
The nanocrystals in the irridophore cells are made of guanine, one of the four base pairs that together make up the 'letters' of DNA, and the lattice of cells is tightened or relaxed depending on the lizard's state of excitation. When calm the lattice is tight, the smaller gaps corresponding to a reflection of blue light, when calm the lattice is looser by up to a third, producing yellows, greens and reds. How they achieve this remains for now a mystery, though they may be expanding and contracting the entire cell. The animals skin also contains yellow pigment, which mixed with blue from the nanocrystals makes the more usual green. Squid and octopi change colour by changing the quantities of pigments in their cells, this is the first mechanism discovered in the natural world to actually change the wavelength reflected using the same trick as opal. Imagine an opal that changed colour when you squeezed it. Ain't nature wonderful?
Loz
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Image credit: Alamy
Includes a cool video: http://bit.ly/1ERTpfN
Original Nature paper, free access:http://bit.ly/1GCqSgi[_
_](https://www.facebook.com/TheEarthStory/photos/a.352867368107647/853501664710879/?type=1&theater#)
nectargems
OOH! This Lithium Niobate may be the one of the MOST AMAZING GEMSTONE I have ever held!! This dispersion is UNMATCHED! 🌈🌈🌈🌈
❌SOLD -
_✨✨ Cut by my good friend @hashnustones
- 46.35carats (19.4mm)✨✨
This man-made material was often used in the optics industry, but when cut into a gemstone, it reveals an amazing color and light performance unlike ANY Diamond or high-dispersion mineral commonly found. ✨Given new industry practices this old-stock rough is becoming increasingly harder to find. 🌀🌀🌀
A MUST HAVE for any collection of rare treasures
Double rainbow off the Baltic Sea
The Not-So-Blue Jay
Just to set the story straight, blue jays (Cyanocitta cristata) are not blue. They're brown. Sort of.
To be more precise, blue jays, and other blue birds, don't have any blue pigment in their feathers. Instead, their feathers are composed of tiny, specialized cells, generally no larger than 0.6 microns. While a feather is growing, the keratin in the cells elongates and separates from water. When the cell dies, the water evaporates, leaving the keratin in a honeycombed structure, called “barbs” in blue jays. These cells absorb red and yellow light and reflect blue light, which is what we see. The size and shape of the honeycomb creates different shades of blue.
Blues, violets and greens are all produced this way, and can be enhanced by the darker layers underneath. An iridescent shimmer is produced when larger, less homogenous spaces are found on the same feather. All of these colors are called structural colors, clearly because they aren't produced by pigments but by the structure of the feathers. The man who discovered this type of light reflecting structure was a British physicist by the name of John Tyndall. The color of the sky, “Tyndal blue” is named for him, as the color of the sky is produced by the reflecting and scattering of light off small particles.
But the blue scattering doesn't end with the sky. Smoke coming from motorcycles and other two-stroke engines often appears blue from reflected light. Even blue eyes are a result of the Tyndall effect. All eyes have a turbid layer in the iris. Brown eyes have melanin in that layer, but blue eyes allow light in. Part of it is then reflected and scattered, leaving baby blues.
Photo Courtesy of Michael Baglole:https://www.flickr.com/photos/mbaglole/
Sundog over English Bay
A summery afternoon over this Canadian locale produced a variety of optical effects based on the different orientations of minute hexagonal ice crystals in the thin wispy cirrostratus clouds. The most obvious are the rainbow sundogs to the left and right near the horizon (seehttp://tinyurl.com/ph8od74). The other two are known as upper tangent arcs and the 22 degree circular halo, phenomena that occur together. The haloes are due to the sunlight interacting with column shaped ice crystals drifting in the air with their long axes near horizontal. The light enters through one face and exits through another, creating this effect. They are much wider than the more commonly seen coloured rings produced by water droplets. Tangent arcs appear at a tangent to the halo and get closer to it as the sun sinks in the sky.
Loz
Image credit: Doug Farmer via EPOD
5 Optical phenomena you will probably never see.
The interaction between the atmosphere, particulates, light and water can create an array of amazing optical phenomena to feast our eyes on- some are more difficult to witness first hand than others. But, at least we have the facility of the internet to show everyone what they are missing, or provide an opportunity to the lucky few witnesses to gloat. Here are five of the rarest optical phenomena you are (un)likely to see, accompanied by a ‘what you need’ supplement to inform you when to have a camera ready and aimed in order to capture these awesome sights. May the odds be forever in your favour!
Number 5: The Fire Rainbow.
Technically, it is known as a circumhorizontal arc, but that’s not quite as much fun to say. This phenomenon is caused by clouds which contain water and ice droplets of nearly uniform size. These clouds diffract sun light which separates the light into different wavelengths, which we perceive as different colours. Although they look similar to rainbows in their colour arrangement; the mechanism by way the light is scattered to produce them is different. Rainbows are the result of refraction and reflection. When light is refracted, it is bent by passing through mediums of different densities, such as water. Reflected light bounces off a surface at an angle equal to the angle it hit the surface at. Diffraction, however, involves light waves being scattered into a pattern; creating what you see here.
You will need:
-Cirrus clouds at least 20,000 feet in the air. -Optimum amount and distribution of ice crystals. -The sun angled so light hits the clouds at precisely 58 degrees.
Number 4: The Moonbow
The principles behind the formation of a Moonbow are quite the same as a rainbow; light is refracted as it passes through water droplets in the sky. These refractive properties of the droplets cause light to be split into a band of colours, more specifically the light spectrum. The only exception here is the light source is no longer the Sun, but the Moon (yes, it is technically still sunlight).
While most of us will have seen a rainbow at least once in our life time, a much fewer number will have had the pleasure to encounter the lunar equivalent. This is because, as the Moon is more variable than the sun, many conditions need to be just right.
You will need:
Number 3- Night Shining Clouds
These rare, mystifying clouds are formed under very restrictive conditions and are only seen in the summer, at latitudes north of 50 degrees. They originate in the layer called the mesosphere; making them the highest cloud formations in our atmosphere. While ordinary tropospheric clouds get their source of dust from things like desert storms, this is not a viable medium in the mesosphere where this dust simply cannot reach. Accordingly, it is speculated that these cloud formations utilise dust particles from outer space, making them extra awesome. Normally, they are far too faint to be seen, but they can be visible when illuminated by sunlight below the horizon.
You will need:
-Latitude north of 50 degrees - Moisture -Space Dust
Number 2: The Green Flash:
The famed Green Flash is a meteorological phenomenon that occurs at sunset and sunrise. The green flash is viewable because refraction bends the light of the sun. The atmosphere acts as a weak prism, which separates light into various colours. When the sun's disk is fully visible above the horizon, the different colours of light rays overlap to an extent where each individual colour can be seen by the naked eye- for a fraction of a second!
You will need:
-1 sun set (or rise) -A long, uninterrupted horizon. The ocean horizon works well. -A very clear day -The ability to not blink helps considerably.
Number 1: The Red Sprite
First noted by scientist in 1989, sprites are bursts of electrical energy that form around 50 miles (80 kilometres) above the Earth. From what is known, sprites send pulses of electrical energy up toward the edge of space (the electrically charged layer known as the ionosphere) instead of down to Earth’s surface. It is speculated that ions and electrons floating about the atmosphere are heated by this field and glow red in response. Why are they so hard to see? Well, they last just a few milliseconds and since they are commonly associated with thunderstorms; clouds block the view from the ground. For this reason, many pictures of sprites have come from flights in orbit.
You will need:
-1 thunderstorm -1 Space Station (optional)
-Jean
All images courtesy of Wikimedia Commons
This amazing photo was taken by Manolis Shamanos in Samos, a Greek island in the eastern Aegean Sea.
As you can see, there is a double rainbow in the image. But, how does this happen?
Firstly, we need to understand how a primary rainbow is formed.
This optical effect occurs as sunlight enters a raindrop. The beam of light is slowed down and is refracted, dispersed and reflected. Light essentially travels in waves of energy and appears white due to the combination of colours in that single wave of energy. When light bends, individual colours will separate with violet light refracting the greatest and red light refracting the least. This is the reason blue is found at the inside of the bow and red on the very outside.
The critical angle of water is 48°, thus any light that hits the raindrop at an angle greater than this is internally reflected towards our eyes. Each ray of light is dispersed at a different angle, which causes the “bow” appearance.
While a primary rainbow is visible when light is reflected once off the back of a raindrop, a secondary rainbow is spotted when light is reflected twice in a more complicated pattern. When a secondary rainbow appears you will notice two things; firstly, the colour order is reversed and secondly the colours are not as sharp as in the primary rainbow.
The reversal of the colour order is due to the fact that the ray of light is reflected twice within the raindrop; the second reflection inverts the order of the colours. Also attributed to the number of reflections is the loss of colour intensity, with each reflection causing the bow to appear dimmer.
Jean.
Alexandrite cats eye Alexandrite (see http://tinyurl.com/dxwv9zo) is a variety of the mineral chrysoberyl (seehttp://tinyurl.com/mvbojuj) that changes colour depending on the relative wavelength richness of the ambient light (ie whether it contains more blue or red wavelengths). The best qualities display a beautiful mint green to raspberry red depending on whether they are viewed in sunlight or incandescent light (firelight or the old type tungsten wire bulbs). Chrysoberyl is also the only mineral allowed to be called cats eye when it displays the phenomenon known as chatoyancy (seehttp://tinyurl.com/makwolr), in which a line of light moves across the stone when it is tilted back and forth in a strong light source. The rarity in the photo combines the two, a decent colour change and a fine and sharp catseye, making it a truly unique piece of nature. Loz Image credit: Gemological Institute of America
Glories
Looking out an airplane window occasionally reveals a strange and wonderful sight: a rainbow-like halo of light encircling the aircraft’s shadow on the clouds below (image 1). This colorful phenomenon is known as a glory. The halo of a glory is composed of concentric rings, each blue in the interior and red outward, dimming with distance away from the center. The shadow at the center of a glory is not required for the glory to occur, but the conditions of bright, direct light that form a glory also form a shadow of the observer.
Relative to the observer, glories always occur opposite the sun, making them uncommon to observe from the ground. However, sunlight and fog at sunrise or sunset are occasionally conducive to glories for observers on cliffs, bridges. Under these conditions, the combination of a glory and a person’s shadow is known as a Brocken Spectre (image 2). These eerie apparitions have been the subject of curiosity and superstition throughout history, with tales and drawings of their observation appearing in several-hundred-year-old records.
The mechanism by which glories are formed is only partially understood. Rays of light enter a droplet of water at a glancing angle, are reflected off the back of the droplet, and then exit the droplet travelling back toward the light source. However, such a directly-returning ray path cannot occur only by simple reflection and refraction of light in a spherical droplet. One possible explanation for such a trajectory is that the light travels briefly as a surface wave along the edge of the droplet before refracting in and out. Another idea is that the light interacts with evanescent wave fields inside the droplet to change its path. The different influence of either effect on different wavelengths of light result in slightly different trajectories, separating the colors into the beautiful observed spectral halo.
-Ce
Information: https://bit.ly/2tCI18D , https://bit.ly/2KfyvSV Image 1: Michel Royon, Wikimedia Commons https://bit.ly/2N8dvvu Image 2: user BrockenInaglory, Wikimedia Commons https://bit.ly/2Muzsna
A double rainbow!
This amazing photo was taken by Wes Eisenhauer in Sioux Falls, South Dakota.
The optical effect of a rainbow is formed as sunlight enters a raindrop. The beam of light is slowed down and is refracted, dispersed and reflected. Light essentially travels in waves of energy and appears white due to the combination of colours in that single wave of energy. When light bends individual colours will separate with violet light refracting the greatest and red light refracting the least.
The critical angle of water is 48°, thus any light that hits the raindrop at an angle greater than this is internally reflected towards our eyes. Each ray of light is dispersed at a different angle, which causes the “bow” appearance.
When a secondary rainbow appears, as in this photo, you will notice two things; firstly, the colour order is reversed and secondly the colours are not as sharp as in the primary rainbow.
The reversal of the colour order is due to the fact that the ray of light is reflected twice within the raindrop. The second reflection inverts the order of the colours. Also attributed to the number of reflections; is the loss of intensity, with each reflection causing the bow to appear dimmer.
Jean
Cue the 'But what does it mean??' comments in 3.....2.....
Reflection rainbows The middle rainbow that is standing vertical between the primary and secondary arcs is an unusual phenomenon, resulting from the sunlight shining as a beam upwards through the same water droplets that are refracting the primary solar rays after being reflected by the surface of the body of water (though wet sand can also produce this optical effect). These appear most often when the sun is low on the horizon at dawn or dusk when the water reflects the solar rays most powerfully, as evidenced in this case by the steep angle of the primary arc. The arcs and reflection bow will draw closer together as the sun sets lower in the sky before vanishing with it into the growing dusk. . Loz Image credit: Manolis Thravalos via EPOD http://epod.usra.edu/ https://www.atoptics.co.uk/rainbows/reflect.htm
When you visualise an iceberg in your mind, most people will automatically manifest an image of huge chunks of white ice. Accordingly, this blue iceberg in Antarctica may come as a nice surprise.
To understand how this happens, we must first look at why we visually perceive most icebergs to be white:
Icebergs come from glaciers and glaciers are formed as a result of snowfall. As water freezes into snow, it becomes crystallized. A close examination of a snowflake reveals a many-faceted crystal, not unlike a cut diamond. These facets or surfaces are capable of reflecting light. Snow appears white for this very reason. As snow accumulates, the structure of snowflakes traps a great deal of air. This is easily seen if you fill a glass to the top with snow, then bring it inside and allow it to melt. You quickly notice that most of what you thought was frozen water, was actually air. As there is a lot of trapped air in snow, light hitting the iceberg is reflected off the many internal surfaces and then visually appears white.
So, why does this iceberg not look white also?
Blue icebergs are in fact very old; they have been through possibly hundreds of thousands of years of thawing, refreezing and compression. As a result, much of the trapped air has been released, reducing the reflective capabilities of the iceberg. Now that the light is no longer being reflected as efficiently, it is instead being absorbed. The weaker wavelengths of light (towards the red spectrum) are quickly filtered out. The blue spectrum, however, has enough energy to penetrate the ice where it either: finds an internal surface to reflect back from or it manages to penetrate the whole way through; thus giving a blue colour. Amazing.
-Jean
For more information about the formation and properties of icebergs; please follow this link: http://science.howstuffworks.com/environmental/earth/geophysics/iceberg1.htm
Photo courtesy of Maria Stenzel_ _
