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2nd Dec 2010 13:08 UTCDavid Bernstein Expert


I was breaking up Quartz yesterday. The Quartz was heavily stained but the only mineral of note I found after breaking apart twenty pieces was Galena. I had been looking for Bismuth which was a possibility given the mine I collected the specimens from. While breaking apart one large piece, a large spark shot up, sort of like what you see when a match head explodes into flame. I then detected a smell of rotten egg, something I'm familiar with since my old elementary school constantly had that smell.

Is what I experienced, the spark that is, triboluminescence? And is the smell related to certain sulfides that may be present in the Quartz? Many thanks.

2nd Dec 2010 13:12 UTCAlfredo Petrov Manager

Not triboluminescence in this case. Probably a speck of pyrite caught fire.

2nd Dec 2010 16:08 UTCDavid Bernstein Expert

-- moved topic --

2nd Dec 2010 16:27 UTCRob Woodside Manager

Could the sufide have been ignited by triboluminescence? Take a couple of quartz pieces into a dark room and after a few minutes for your eyes to adjust, bash them together and see if there is any light. I'm not sure how different getting sparks off flint to start fires is any different than triboluminescence. Maybe others could comment.

2nd Dec 2010 16:34 UTCAlfredo Petrov Manager

Although, as Rob points out, milky quartz is frequently triboluminescent, triboluminescence is a cold light; I don't think it could start a spark.

2nd Dec 2010 17:05 UTCRob Woodside Manager

Ahhh!!! Thank you Alfredo.

2nd Dec 2010 17:50 UTCDonald Lapham


Can't pressure on quartz generate a piezoelectric static discharge and this discharge generates Ozone. I seem to remember detecting the faint smell of Ozone while demonstrating triboluminescence using my Brazilian river tumbled quartz crystals.

2nd Dec 2010 18:09 UTCRob Woodside Manager

Thanks Don. I'm sure the piezoelectric effect is behind the sparks struck from quartz used for flintlocks and fire starting. I don't know what xl they use in B B Q igniters.but they use this effect. Alfredo makes the point about cold light. Presumably any demonstration with Quartz might also show piezoelectric sparks.

2nd Dec 2010 18:15 UTCAlfredo Petrov Manager

Sorry to be so negative today, Rob, :( but the sparks struck by quartz on tools, etc, are actually chips of iron catching fire; the quartz is used only for its hardness, to scratch off thin microslivers of iron and heat them by friction to their ignition point. I have no idea what voltages are produced by piezoelectric effects, but I'll buy you a stiff drink in Tucson if they are anywhere near high enough to cause a spark in air!

2nd Dec 2010 18:23 UTCRob Woodside Manager

Alfredo you may well be right, but 3 Megavolts/meter is only 3 volts/ millimeter which seems more attainable.

2nd Dec 2010 19:16 UTCHenry Barwood Expert

Hi Rob,

Wouldn't 3 volts per millimeter be 3 KV/meter, not MV?

Triboluminesce is very common in quartz. I have found over the years that high pressure quartz, such as rose and blue quartz from plutonic pegmatite cores, is often highly triboluminescent. The phenomenon is poorly understood.

2nd Dec 2010 19:22 UTCDavid Bernstein Expert

Just so I'm clear guys because you are getting to the point where I have to look up things-(I never heard of piezoelecticity but now I know how my grill operates)-in my scenario, it's the consensus that I am not dealing with either tribluminescence or piezoelectricity?

2nd Dec 2010 19:35 UTCAlfredo Petrov Manager

IMO, David, those are electrical phenomena, and you are instead dealing with a chemical phenomenon - the burning of a tiny flake of pyrite in the oxygen of the air. It was an ancient technique for starting fires - chipping a lump of pyrite with something hard, like quartz or chert. Later, people used iron for the same purpose, except you'd strike the iron with the rock instead of the rock with the iron. Once in a while a spark comes off of my rock hammer when I hit a very hard rock - probably a chip from the iron head of the hammer flying off, on fire.

2nd Dec 2010 19:36 UTCRob Woodside Manager

Arghh mm = 10-3 m. I could be smart and say I meant micrometers, but I screwed up!!! Thanks Henry. However over the very small distances (possibly micrometers???) much smaller voltages per distance are required for dielectric breakdown. The length of the sparks, distinct from the shards of glowing fragments, would give the voltage difference. This is not large. It is more likely as Alfredo points out that the flaming shards are responsible for ignition.( edit: Alfredo's last post appeared while I was composing. Of course, the second surface- I hadn't realized that the strike plate was the cause!!!)

I think almost all friction and abrasion is poorly understood. Recently it was found that "mountainous" asperities on abraiding surfaces got caught and released in a stick /slip action setting the "mountain" into vibration which broadcast phonons into the main xl. In this way the "friction" heated the xl. That's a lovely mechanistic view, but I'm not sure that's why my hands warm up when I rub them together.

2nd Dec 2010 19:48 UTCRob Woodside Manager

Thanks David, this is a learning experience for me too! Although Triboluminesence and piezoelectrity are well known in Quartz, I suspect that Alfredo is right and that it was sparks from your hammer that ignited a sulfide. However you should have smelled acrid SO2 rather than H2S. Perhaps some was liberated from the galena on fresh fracture and that had nothing to do with the sparks.

4th Dec 2010 06:29 UTCRay Hill Expert

Maybe I need my physics re looked at..but in my poor memory, I thought that piezioelectric charges were generated by pressure applied to very thin plates or slices of pure quartz and either the point pressure, or the release of that pressure generated a charge across the thin plate. If this bit of memory is correct, then the spark caused by abrading or striking the quartz would more likely be some coefficient of friction and pressure combined causing a release of energy in the form of heat ....which , is not a piezioelectric discharge, but something this correct or somehow confused...?

4th Dec 2010 19:16 UTCAdam Kelly

Ray, that sounds right to me,

but my understanding of some of these factors is rather elementry.

5th Dec 2010 04:13 UTCBill Lechner Expert

Weloganite is also triboluminescent. I remember being surprised when I was splitting Francon material and it produced a blue flash due to the presence of Weloganite.


5th Dec 2010 12:05 UTCPeter Andresen Expert

Leucophanite is also triboluminiscent, gives a orange-red colour when scratched hard with a nedle.

5th Dec 2010 17:22 UTCHenry Barwood Expert

Peter and Bill,

I'm only familiar with quartz and fluorite. Has anyone done spectroscopy on these various triboluminescent minerals? If the effect were coming from electrostatic or piezoelectric forces, you would expect the UV/blue end of the spectrum to dominate, not red.

5th Dec 2010 19:15 UTCRock Currier Expert

I was looking at the species page for Weloganite to see if it listed triboluminescence as one of the properties and also checked the edit page and could not find a place where this property could be reported. Did I miss something?

5th Dec 2010 19:55 UTCRob Woodside Manager

That's good info on Weloganite (ashame to crack an xl) and Leucophanite that we should capture. Currently the two places for triboluminescence in the data base would be under comments on breaking or electrical properties. I've put this info in both places for both minerals.

Right now "pyroelectric" is listed for Weloganite under electrical properties. Both Pyroelectricity and Piezoelctricity requires an xl without an inversion centre, so you won't see that in Fluorite, but could well occur in Weloganite or leucophanite.

5th Dec 2010 20:30 UTCJames Christopher

Sphalerite is also triboluminescent.

5th Dec 2010 22:57 UTCDean Lagerwall Expert

Quartzite when broken can spark and produce ozone. I recall from when I used to rock climb at Senica Rocks, WV (in my younger days) that when pieces of the broken Tuscarora quartzite hit each other we could smell the resulting ozone as we hiked up to the climbing area. I was also told that when the "Gendarme" (a large boulder perched on the top) fell, the ozone was noticable throughout the valley.


6th Dec 2010 06:16 UTCHenrik Friis

Hi Peter,

interesting with leucophanite. I am just wondering how to distinguish between triboluminescence and thermoluminescence in a case where you scratch a sample. I know leucophanite can have a very strong TL response (overloaded a detector at Daresbury), but I don't know how much heat is generated when a sample is scratched. Just thought that the described observations here may have a series of origins.



6th Dec 2010 17:09 UTCRob Woodside Manager

Hi Henrik, Yes there is a problem with Triboluminescence as when you scratch something you get very high LOCAL temperatures and pressures. For an xl without an inversion centre both Pyro and piezo electricity could be involved. However the examples of sphalerite and fluorite cannot be pyro or piezo due to their symmetry. So there is more to this story, but I don't know what it is.

6th Dec 2010 22:37 UTCRonald J. Pellar Expert

Pyroluminescence is the release of light by heat. It is due to the relaxation of electrons from trapping centers to their ground state and in ceramics can be used for dating them (the number of electrons raised into the trapping centers is a function of the time exposed to gamma or natural radiation).

Piezioelectricity is a voltage induced by stress and is specific to crystal directions. Sufficient stress can cause a voltage high enough to cause a spark.

Triboluminescence is the release of light due to pressure. I remember a camping trip to Mt. Palermo where after dark we threw chunks of quartzite against a wall and watched the resulting flashes. Lots of fun!

There may be a relationship between the pressure and stress but not likely. The piezioelectric effect can be generated by a slow prolonged stress whereas the triboluminescence cannot be generated with slow application of pressure. It usually requires a rapid application of pressure.

The sparks were generated by the same principle that a flintlock rifle ignites the gun powder, i.e., quartz against iron or steel generating a hot spark.

7th Dec 2010 04:51 UTCRob Woodside Manager

Thanks Ronald.

I think triboluminescence has to do with light being emitted on fracturing, so that symmetry is irrelevant. I don't know of anything that glows when a constant or variable pressure is applied.

I think the relation between pressure and stress is well summarized in the stress tensor. The stresses are the "off diagonal" terms in a matrix representation of the stress tensor. Since the stress tensor is symmetric, it can be diagonalized with an appropriate coordinate transformation and the diagonal values are the pressures or the principle stresses. In an ideal fluid, the three are equal and this is the number that is given for atmospheric pressure in weather forecasts. If rocks were ideal fluids, the pressure due to the weight above (lithostatic pressure) would be the same in the horizontal directions.

Thanks to Alfredo we understand the necessity of the strike plate in flintlocks.

7th Dec 2010 12:04 UTCPeter Andresen Expert

Could triboluminiscence be explained by the enery released when molecular bonds are broken?

As Rob mentioned, I have never heard of any minerals lighetening up by preassure alone - that vould be pretty easy to observe (and if occuring - miners vould sometimes not need to bring a torch?!;)). I had my larger trimmer inside a dark cabinet, and once trimming down some quartz rich samples, I could observe flashes of light just as the quartz broke, not as sparks - more like an internal pinkish-red colour...


7th Dec 2010 16:38 UTCRob Woodside Manager

Yes Peter I think you are right. I think the cold light is resulting from relaxing the disrupted electronic states or bonds when something is fractured. To sort this out, the start would be to get good triboluminescent spectra and then try to imagine the electron states whose energy difference gives the spectra. The best I can find is that electron states in solids are Bloch waves, which for insulators seems nuts.

Are there any published triboluminescent spectra?

7th Dec 2010 18:25 UTCRoger Curry

A good video on YouTube with Europium Tetrakis (Dibenzoylmethide) Triethylammonium crystals :
triboluminescent crystals

Spectra :
Sugar triboluminescence spectrum



7th Dec 2010 19:59 UTCRob Woodside Manager

Wow!!! Ask and ye shall receive!!! Thanks so much Roger for these interesting links. It looks like there may be several different triboluminescence mechanisms.

Without a spectrum you can't say for sure, but the triboluminescent colour in the first link looks like a typical Europium UV fluorescence. Do triboluminscent quartz, sphalerite or fluorite fluoresce the same fluorescent colours under UV?

In the second link the triboluminescence emission of winter green has an extremely broad peak, much wider than the disulfide UV fluorescence peak in scapolite which Earl ascribed elsewhere as due to temperature. l wonder what the temperature dependence, if any, there is in triboluminescence? To get a molecular nitrogen spectrum matching the triboluminescence spectrum out of sucrose which contains no Nitrogen shows how complicated this stuff can be, Perhaps the sucrose triboluminescence results from x-rays produced in breaking sucrose, as in the Nature link (buried in the first link), hitting the molecular nitrogen in the surrounding air?

7th Dec 2010 20:21 UTCDavid Bernstein Expert

OK, Roger, I'm going to use a very non-scientific term for that first video-COOL!!!

Many thanks for posting.

12th Dec 2010 02:58 UTCFranklin Roberts

Hello gang, I'm back!

I first noticed the striking pinkish-orange luminescence of milky pegmatite quartz while sliding down a quartz pile on my butt on a moonless night in November of 2004. Charlie Thompson and I were night collecting at the Badu Hill Pegmatite in Llano County, Texas with our UV lamps and scintillators. After sliding down the quartz, Charlie and I noticed hundreds of bright yellowish flashes of light directly beneath my backside and a lot of feeble flashes in my wake where the quartz cobbles were still settling after having been disturbed by my passage. A strong odor of garlic was also noticed during the phenomenon, leading me to suspect that something other than triboluminescence was at work here. Because of the highly specific conditions under which the glow was created, I dubbed the phenomenon "proctoluminescence" in my field notebook.

The milky white color of Llano Uplift quartz is due to trapped microscopic gas bubbles in clear massive quartz. Rubbing two pieces of this quartz together vigorously produces a pinkish-orange flickering light reminiscent of a distant thunderstorm on a warm summer night along with the same strong odor of garlic. I thought that the garlic odor had a familiar smell to it, but it was Charlie Thompson who keyed in on it. Charlie, who designs silicon microchips for a major chip manufacturer, immediately recognized the garlic odor as silane, (SiH4), a poisonous pyrophoric gas used in the fabrication of silicon integrated circuits. Silane reacts violently with atmospheric oxygen and humidity, catching fire instantly upon contact with air. Workers in wafer fabrication facilities are trained to recognize the aroma of garlic as a sign of a dangerous silane leak. Here in Austin, hardly a month goes by without AFD HAZMAT being called out to handle a silane leak at one of the major chip fabrication facilities here. More often than not, these leaks result in small fires as no ignition source is required. There are several industrial gases used in chip manufacture that are pyrophoric (self-igniting) and give off a garlic aroma. Germane (GeH4) and phosphine (PH3) are two that come to mind.

I suspect that the microscopic gas bubbles in the quartz are in fact silane, created when the still-fluid quartz catalytically reacted with superheated water during the later stages of pegmatite cooling. I have a pet hypothesis that rubbing two pieces of this quartz together in the dark ruptures gas bubbles near the surface, releasing trapped silane which then ignites in the air, generating flashes of light and the telltale garlic aroma.

I haven't researched this hypothesis, but it wouldn't be hard to test. Subjecting a thin slice of Llano milky quartz to microwave or RF excitation should cause any gas molecules trapped in the quartz to glow with characteristic spectral lines. Identification of the gas would be a simple matter of comparing those lines to those of known gases using a simple spectroscope. Crushing a sample of the quartz in a sealed container under hard vacuum would free up a tiny sample of the gas for further study.


12th Dec 2010 18:46 UTCAdam Kelly

Welcome back Franklin.

12th Dec 2010 20:00 UTCRock Currier Expert

We are again grateful to have Franklin back to illuminate proctoluminescence for us. It will undoubtedly be picked up and included in all future mineralogy texts in the future.

12th Dec 2010 20:38 UTCRob Woodside Manager

Franklin, It's great to get more of your interesting and thought provoking posts. As I was slowly reading your post I came to the same hypothesis. Probably more to do with your writing skills than any grey matter I might have. So triboluminescence is complicated stuff with lots of potential mechanisms. What you say makes perfect sense and aches for experiment. However if you are right, the pyrophoric light should also be accompanied by heat, so maybe this is "proctoluminescence" and not the purportedly cold light of triboluminescence. It may be that triboluminescence produces heat, but just not very much of it? The fracturing energy must go somewhere. I can't believe it is 100% efficient light conversion. If you are right this quartz will not have any UV fluorescence remotely resembling the colours of "proctoluminescence". What about sphalerite and fluorite?.

12th Dec 2010 23:49 UTCDean Allum Expert

Hi Frank,

I hope all that typing isn't wearing you out.

I think you are mentioning a type of triboluminescence that is unique to the milky quartz of the Llano uplift (it does sound like a powerful mechanism). You would probably agree that triboluminescence is more like thermoluminescence in other materials such as in the video that Roger posted.

I keep on thinking about something you wrote when you taught us about thermoluminescence. The underlying defect recombination produces photons with several electron volts of energy. These are in the UV spectrum. These higher energy photons are converted to light in fluorescent minerals (convert UV light to visible light) so that we can see that they are thermoluminescent.

There may be many more thermoluminescent materials that we do not know about since they are NOT also fluorescent. Perhaps we could detect that they are thermoluminescent by heating them adjacent to a phosphor, such as glass from a fluorescent light bulb. These potential UV thermoluminescent minerals need to be transparent in the UV spectrum. Of course exposure to gamma radiation is also a prerequisite for thermoluminescence.

The F centers which you mentioned have been well studied in the alkali-halides, so I wonder what are some good mineral candidates?

I have a non-fluorescent fluorite and a halite crystal which have been sitting under a uraninite crystal for 2-years in an attempt to get a color change (hasn't happened). Over the Christmas break, I will try the heating/phosphor experiment on these.

Best regards,

Dean Allum

13th Dec 2010 18:02 UTCRock Currier Expert

George Rossman of Caltech was asked to provide expert testimony in a law suit between a party that contended that they were injured by the power company, contending that that in some work they were doing on a tower on a mountain side had caused boulders to fall down the mountain creating sparks that causes a forest fire that had burned down some structures? He supervised tests with boulders swinging on the end of crane mounted tethers against other rocks and measured the amount of heat generated and concluded that boulders hitting other rocks would not have likely caused the fire. I hope I have dredged the essence of the story from my memory more or less correctly. For the particulars of just what instrumentation he used to measure the heat or sparks generated you would have to contact him. It was an interesting story. In spite of his work, the power company had to pay up.

13th Dec 2010 23:17 UTCFranklin Roberts

Dean, your phosphor experiment sounds interesting. Perhaps a setup similar to liquid scintillation counting would work. This would involve combining a solution of fluorescent dye with a small quantity of sand-sized particles of the mineral under test in a pyrex vial. The vial would then be heated while a photomultiplier tube monitors any light that might be generated by the dye. Most PM tubes can see well into the UV, so the dye might not be needed at all.

One characteristic of the light emitted from the Llano quartz that distinguishes it from the other triboluminescent minerals I've encountered in the Uplift is the rapidity with which it extinguishes itself. The light emitted by the quartz would best be described as a flicker, having an extremely fast rise and decay. The triboluminescent fluorite and tremolite I've collected exhibit a time vs luminosity curve having a decay of several seconds after being struck or rubbed, almost like a phosphorescence decay curve. Fluorite from the Petrick Pegmatite will leave a fading lavender streak when rubbed on a chalk board. A tremolite outcrop in the Sunrise Beach area of Llano County will leave a blood-red luminescent spot when struck with a crack hammer in the dark. That glowing spot can sometimes take ten seconds to fade to black.

I'm not sure that you'll be able to generate enough color centers in your fluorite using uraninite as your gamma source, at least not in any useful time frame. I've read of it being done in a couple of days using cobalt 60 sources emitting hundreds of rads/hour of gamma. I'd be surprised if you registered more than a few millirem/hr with your natural gamma source. Would you like some thermoluminescent fluorite or Llano milky quartz to experiment with?


13th Dec 2010 23:54 UTCDean Allum Expert


Thanks. You already sent me a Petrick fluorite, so I will take a look at its' triboluminescence.

Rather than use a complicated scintillation setup, perhaps I will learn how to do a long exposure on my camera.

I know someone with access to CO-60, so please suggest some mineral types. The concept of a nuclear powered flashlight is appealing!

You've probably already seen the little ones from this fun company:
United Nuclear

-Dean Allum

14th Dec 2010 06:49 UTCFranklin Roberts

While we're on the subject, here's a related luminescent property of the Llano milky quartz that I've observed in the field. Normally, the quartz is absolutely non-fluorescent under short or long wave excitation. If however the quartz is shocked, such as when subjected to blasting, it becomes intensely fluorescent in the vicinity of shock-induced hazing or fracturing. The induced fluorescence can be pink, yellow or sky blue under shortwave UV. I have not tested it under longwave excitation. At first, I suspected that the fluorescence might be due to contamination by reaction products from the explosives, but the induced fluorescence was visible deep within the shocked quartz, well away from the blast holes, but still in areas subjected to internal shock waves. Follow-up investigation showed that the new fluorescence is also present in the hazing around hammer drill holes even before any explosives are loaded. It even shows up in quartz that has been shattered by hammering.

This phenomenon isn't limited to quartz. Microcline and pink granites containing microcline will become brilliantly fluorescent along blast fractures after a shot. Instead of the beautiful vermillion red shortwave fluorescence characteristic of microcline, the shocked material exhibits a brilliant bluish-white glow similar to that emitted by laundry detergent. Deep fractures not directly exposed to the explosion glow just as brightly as those nearest the shot, suggesting that contamination by the explosive or its reaction products is not the source of the fluorescence. Washing will not remove it either.

Any ideas?


14th Dec 2010 09:43 UTCNoah Horwitz

In my limited experience, it seems like the triboluminescence or piezoluminescence of milky quartz is fairly general. I know some museum shops sell "lightning stones" or some such that appear to be ordinary pebbles of milky quartz. I've seen the same effect with some that I picked up from my yard: an orange flash on hitting or rubbing two pebbles together. While it's possible that these also came from a pegmatite, there are few/none near where I live, making this less likely (most likely metamorphic). My pieces don't show any fluorescence under longwave UV after this striking.
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