FMF - Friends of Minerals Forum, discussion and message board

[Maxilos]

Hi,

There is a simple question I'd like to ask: how do minerals form?

I also want to make another question deeper inside that question: How and why are some minerals fluorescent, and how and why can you see daylight fluorescence on Rogerley fluorite?

I have been looking for the answers a year now, I hope you gan give them.

Mark

[Matt_Zukowski]

If you want a real answer, you should go to an introductory textbook on minerals & mineralogy.

Minerals form whenever thermodynamically favored. This is a fancy way of saying when the mineral form is more stable or less energetic than the dissolved or melted form.

Minerals forming from a melt - So when lava cools, eventually it gets to a temperature when the atoms "like" to stick together in an arrangement called a mineral. By "like" I mean it requires less energy to be a mineral than to remain in the melt.

Minerals forming from a solution - A solution, running through rocks, carries a dissolved load. If something changes (temperature, concentration of solutes in the solution because the solution encounters other water or a different rock type, etc.) then the solution may precipitate a mineral. Again, the mineral forms only if by forming the mineral, the energy of the system decreases. Evaporation is a simple case of minerals forming from solution - a particular mineral will start to precipitate from an evaporating solution when energetically favorable to do so.

As to fluorescence, atoms in minerals have electrons. These electrons can inhabit different energy states. Like mineral formation, nature like to be in the lowest energy state. But in this case, a photon (light) strikes the electron, causing it to jump to a higher energy state. When the electron falls back to its original state, it emits another photon with energy equal to the distance of the fall between the excited state and its base or ground state. If the photons of light hitting a mineral are of a too energetic for us to see, but the energy of the photons given off when the electrons fall back to their ground state is such that we can see them, then we call this fluorescence.

[Matt_Zukowski]

As to Rogerly fluorite, you can see daylight fluorescence because it is incredibly fluorescent. All fluorescent minerals fluoresce in daylight, because the sun emits photons of many different energies, and some of those photons are energetic enough to knock electrons up to a higher energy state. But most minerals do not have the capacity of Rogerly fluorite to produce fluorescence. And so the fluorescence of most fluorescent minerals is too weak to see (i.e. they do not fluoresce so much that you can see the fluorescence in daylight).

[Maxilos]

Thank you,

So phosphorescence must mean that the atoms catch a photon and store it till it is full. than the atom will start emitting them to a few seconds after the UV-light is turned of!

I have one last question, probably also the most difficult one: what atoms cause the fluorescence, and, if you know, what colour do they give?

Mark

[Matt_Zukowski]

It is not that atoms catch photons. Better to think of it as the photons knock the electrons up to a higher energy level. The electrons fall back to the base state either instantaneously or over time. If they fall back over time, we call that phosphorescence.

It is better not to think that atoms cause fluorescence. Instead, certain atoms in certain arrangements have electrons that can be knocked up to a higher state temporarily.

You really should just google fluorescence. There is lots of info there.

[Maxilos]

Ok thank you, I will.

[Jesse Fisher]

Rogerley fluorite (as well as fluorite from many other mines in the Weardale region of Northern England) is strongly fluorescent, particularly to long wave UV. Natural daylight contains a fair amount of light in the UV range of the spectrum. This is what gives us sunburns if we over expose ourselves on sunny days. This UV component of the solar spectrum will cause any fluorescent mineral to fluoresce. Most times the response is too weak to see and the effect is overpowered by by the brightness of the visible portion of the daylight spectrum. It is the very strong UV fluorescence of Weardale fluorite that allows us to see the effect in daylight.

[chris]

And to complete what Matt said most of the time crystals get there color because part of the crystal structure is replaced by a different element changing light absorption properties. For example some fluorites contain rare earths. if it contains a lot of Samarian Sm2+ it will turn green, if it contains O3- replacing 2 F- it will turn yellow,... pure fluorite being colorless. You can apply this to smoky quartz as well, and so on...

Christophe

[chris]

Jesse, I think you posted at the same time. Do you investigated on what turns Rogerley fluo green ? is it the same explanation as the one I gave ?

Thanks

christophe

[Maxilos]

Chris, you said something about samarium (Sm2+), ozonide (O3-) and others replacing other atoms. Can these atoms do (meaning the Sm2+, O3- etc.) something with shape, reactions, hardness and luminescence.

Thanks in advance

Mark

[chris]

[Jesse Fisher]

Bonjour Christophe,

Weardale fluorite is known to contain elevated levels of a series of Lanthanide-series elements (REEs), including samarium. The green color of Rogerley fluorite (and other Weardale locations including Heights and the Cement Quarry) is unstable and will fade over time with exposure to direct sunlight. This suggests that the color is the result of some structural defect that is slowly annealed by the energy input of the sunlight rather than the action of a specific metallic chromophore, which one would expect to be stable. Perhaps the structural defect is caused by the substitution of one or more of the REEs for calcium in the fluorite structure.

Cheers,
Jesse

[Maxilos]

I have an other question, so I restart this topic again.
I discovered that Europium ions (Eu2+) in fluorites causes a blue fluorescence. I also found out that yttrium ions (Y3+) cause a yellow fluorescence. My question is: how about purple, red, green and white, what elements cause fluorite (and mayby others) to fluorescence in those colours?

I hope you can help me,

Mark

[Maxilos]

Hi,
Since I'm quite interested in fluorites and fluorescence -what you might have noticed- I have a question about the colours for a change. Jesse F. told me that samarium (Sm2+) ions plus other REE in fluorite give a blue fluorescence in sunlight. I read on the Internet that yttrium (Y3+) ions give a yellow fluorescence. My question is: what elements cause fluorite to fluorescence in the colous: purple, red, green, etc.

Thanks in advance,

Mark

[Jesse Fisher]

Fluorite from the North Pennines Orefield (Weardale and surrounding areas) in England are highly fluorescent (bright blue-white) under long-wave UV. The fluorescence is strong enough that in some cases the fluorite will show a color change due to the UV present in daylight. Purple fluorites such as those from the Boltsburn and Frazer's Hush mines will become a more intense purple whereas greens from the Rogerley and Heights will take on blue overtones.

Fluorite from the region is known to contain elevated levels of a suite of Rare-Earth Elements, including yttrium ytterbium, samarium, europium, cerium, and others. Fluorite from nearby areas such as North Yorkshire lack this elevated REE concentration and are non-fluorescent, so it has been speculated that the REE content of Weardale fluorite is responsible for the strong fluorescence. I have never heard that the fluorescence has been attributed to any one single element, however.

Cheers,
Jesse