Chlorophane

Mindat defines chlorophane as a fluorite variety giving off green thermoluminescence (main feature!), and states that its color is reddish and that it shall fluoresce green.
The green thermoluminescence as a main feature corresponds to Dana 7, but Dana does not specify the daylight color.
The notion of a reddish color corresponds to the description of a Franking, NJ material - see [www.njminerals.org]. Thermoluminescence color is "teal", i.e. bluish-green. BTW, chlorophane is not listed for Franklin on Mindat.
The Badu Hill fluorite photo [www.mindat.org] states that its color is dark purple and its thermoluminescence color is blue-green, although it looks just blue on the photo. Is it chlorophane if it's dark purple?
There are some sources that define chlorophane as green fluorite. For example, green fluorite from the Morefield mine, Amelia Co., VA, is called chlorophane by Kunz (1884) and by Glass (USGS, 1935), and it shows green thermoluminescence (sic!), yellow-green fluorescence and phosphorescence ... but, well, it is green in daylight, not red.

Could someone please clarify what kind of fluorite is correct to call chlorophane?
What shall be the daylight color - green, red, dark purple?
What shall be the thermoluminescence color - green, bluish-green?

Thanks in advance.

The fluorite(chlorophane) that I have collected in Franklin is a brownish-purple. It does have the characteristic green response under uv shortwave. Gary

Here is an attempt to photograph Franklin "chlorophane" both in daylight and under SW UV.

At the time that I collected it (in the 1970s) it was regarded as "typical" chlorophane. But I'm not sure that really means anything much. A lot of fluorite does all the things that supposedly characterize chlorophane: fluorescence, phosphorescence, thermoluminescence and triboluminesnce.

I have chlorophane from McGuire Pegmatite in Colorado, teal thermoluminescense, green fluorescence, and phosphorescence. It is greenish to a greenish brown, some maybe having purplish brown.

Very nearly all of the authoritative sources I've consulted, both just now and in years past, have defined chlorophane as a variety of fluorite that shows a green (teal green) phosphorescence when heated. An early synonym for the substance, "pyroemerald," hints at the same property and links the concept of heating to the definition. Daylight color has nothing to do with it. However, both the name of the material (chlorophane, "to appear green") and some poorly worded definitions have led some to suppose that chlorophane is any fluorite that is green in daylight. One such definition is "Chlorophane: a green thermoluminescent fluorite." Oh, for that missing hyphen! Had that definition been written "a green-thermoluminescent fluorite" it would not have been ambiguous, but as written it probably led some people astray.

Thanks to all of you who responded.
Your info on local material doesn't seem to contradict what Earl wrote and what was exactly my point: the defining feature shall be the green thermoluminescence (i.e. glow caused by heating, as opposed to fluorescence caused by UV light), and not the daylight color, the UV fluorescence or anything else.

If the Mindat managers agree, can we get the definition corrected in Mindat?

Here is an excerpt describing chlorophane from Amelia Co., VA pegmatites - taken from Glass, J.J. (1935), The pegmatite minerals from near Amelia, Virginia: Amer Mineralogist 20:11:741-768. She is very clear on what defines the chlorophane variety of fluorite:

"One of the most remarkable varieties of fluorite known is the chlorophane associated with microlite and other rare
minerals in the pegmatite dikes at Amelia, Va., where it occurs at both the Rutherford and Morefield mines. Most of the material is extremely fractured, so that it readily crumbles when touched. This fragile variety is pale fluorite green in color. Early observers noticed the unusually strong fluorescence exhibited by this fluorite while subjected to heat just below redness. In addition to the fluorescence, a brilliant light green phosphorescence is obtained when the mineral is exposed to ultra-violet radiation.
After exposure to sunlight, these chlorophane specimens produce dense images on a photographic plate similar to those produced by radioactive substances. This photographic effect is not obtained, however, on repeating the experiment with a sheet of black paper interposed between the specimen and the plate, but the effect is marked when a piece of colorless glass is interposed. After the specimens had been kept in darkness for several hours they did not
produce photographic images. The radiation phenomenon appears to be due to some solarization effect.
The same specimens were tested in a gold-leaf electroscope. The specimens that had been exposed to sunlight showed a remarkably strong activity response (.093), but after they had been kept in darkness for 24 hours no activity response could be observed."

It was corrected in 2007

Rob,
It still says Colour: Reddish pink, red, red-brown.

That is the usual colour of Thermoluminescent fluorite, ie chlorophane I would even add purple, but many purple fluorites are not thermoluminescent. When the purple is blotchy that usually indicates radiation damage that is the source of thermluminescence. Fluorite will also thermoluminesce reds and pinks but that is not chlorophane. The final colour of chlorophane is a dull pale green after it has finished glowing teal. I'm surprised gren fluorites thermoluminesce. I'll add green to the colours.

Thanks, Rob.
I don't know, there might be some other possible colors, in addition to the listed colors.
Would it make sense to add some verbiage stating that the daylight color is not relevant for the fluorite to be called var: chlorophane, just to underpin the definition?

According to Manuel Robbins book "Fluorescence: Gems & Minerals Under Ultraviolet Light" 1994, Geoscience Press, Phoenix, reddish daylight color is typical but what is essential is green fluorescence/thermoluminescence. Certainly the material was reddish at the classic Amelia, Virginia locality. Large quantities were found a various places in and around Old Mine Park, in Trumbull, Connecticut (in cross-cutting hydrothermal veins with quartz, topaz, muscovite). Some is reddish, but plenty is colorless or even smoky (especially at the new construction site on Corporate Drive), yet all fluoresce the same brilliant bluish-green under SW with green phosphorescence.
Two points of caution, sunlight exposure destroys the fluorescence, so immediately put it in containers upon collection and keep it out of the light. Heating also destroys the fluorescence. So if you are going to heat a piece to demonstrate the thermoluminescence, use a piece you care to sacrifice. Once cooled, it will no longer fluoresce or thermoluminesce. And any red daylight color will be gone.
I think a lot of colorless chlorophane is present at historic sites but was not collected because it is easy to overlook (looks like quartz), then once noticed it has usually been in the sun too long and has lost its fluorescence, so is not recognized as chlorophane. At the Corporate Drive site, I dug much colorless fluorite out of freshly exposed veins and immediately put it into containers (it was day time) and it fluoresces beautifully. Came back there at night with a UV lamp a few weeks later and there was not a trace of green fluorescence as whatever was laying about was killed by sunlight.

Out of curiosity, can anyone date the "chlorophane" description from Amelia Courthouse? Barringer Hill, Llano Co., TX was reported in the Llano newspaper to have fluorite that would become luminescent in tha miner's hands. At about the same time, the paper reported that the miners were sure the mine was "cursed" because of the sever "sunburns" the miners recieved after a week of work (copius amounts of uranium & thorium). This was in the 1870s or 80s.

Don

Harold,
The Amelia material was and is green, not reddish - please see my quote from Glass (1935).

Don,
In response to your question:

Science, Vol. III (Jan-Jun 1884), available on Google books, describes chlorophane studies by Kunz:
"...At a recent meeting of the New-York academy of sciences, Mr. G. F. Kunz stated, that while unpacking some specimens of fluorite from Amelia county, Va., he had noticed the display of phosphorescence, a pale greenish light, by the mutual attrition of the specimens, the same being excited also by the warmth of the hands. By the heat of a candle, this phosphorescence was increased, and, on a red-hot stove, became a deep emerald-green. This led Mr. Kunz to examine fluorite from over a dozen localities, and he found that only chlorophane yielded phosphorescent light by attrition. In Phillips's Mineralogy, edition of 1823, a specimen of fluorite, described by Pallas, from Siberia, is mentioned, which yielded light by the warmth of the hand. The fact that attrition will cause phosphorescence, Mr. Kunz considered new; and as the same result was produced by chlorophane from Branchville, Conn., it was looked upon as a new distinguishing characteristic between chlorophane and common fluorite..."

Also, the Mindat article [www.mindat.org] is quoting Kunz (1891): "Among the associated minerals I observed quartz, feldspar, mica schist and chlorophane. This is the chlorophane mentioned by Pallas, so highly phosphorescent and sensitive that it emitted light by the heat of the hand."

In his "Magic of Jewels and Charms" (1916), available on Google books, Kunz wrote:
"... A chlorophane is also found in microlite localities of Amelia Court House, Virginia. The writer made a series of experiments and noted that some of these specimens emit a phosphorescent light at low temperature. The material occurs in Siberia, and Pallas describes a specimen from this locality. When subjected to the heat of the hand, it gave out a white light, in boiling water a green light, and when placed on a burning coal a brilliant emerald-green light, visible at a considerable distance. Similar phenomena have been observed by the writer, who has found that very slight attrition, even the rubbing of one specimen against another in the dark, will produce phosphorescence [Kunz, Gems and Precious Stones of North America, 2nd ed., New York, 1892, p. 183]."

The Edinburgh encyclopaedia, Vol. 13, 1832, by Sir David Brewster, available on Google books, writes about fluorite in general:
"When two fragments are rubbed against each other, they become luminous in the dark. When gently heated, or laid on glowing coal, it phosphoresces, (particularly the sky-blue, violet-blue, and green varieties) partly with a blue, partly with a green light. When brought to a red heat, it is deprived of its phosphorescent property. The violet-blue variety from Nertschinsky, named Chlorophane, when placed on glowing coals, does not decrepitate, but soon throws out a beautiful verdigris-green and apple-green light, which gradually disappears as the mineral cools, but may be again excited, if it is heated; and this may be repeated a dosen of times, provided the heat is not too high. When the chlorophane is exposed to red-heat, its phosphorescent property is entirely destroyed. Pallas mentions a pale violet blue variety spotted with green, from Catharinenburg [modern Ekaterinburg, Urals, Russia - M.H.], which is so highly phosphorescent, that, when held in the hand for some time, it throws out a pale whitish light; when placed in boiling water, a green light; and exposed to a higher temperature, a bright blue light."

So, based on all those writings, can we conclude what is really the defining characteristic for chlorophane - thermoluminescence alone or a combination of thermoluminescence and triboluminescence? And what color of thermoluminescence, as it depends of the heating temperature?

Sorry, Robbins (1994) says red is typical "of most of the chlorophane" in general, he wasnt referring specifically to the Amelia material for which he does not give a specific daylight color. He does say that the name "chlorophane" was given to fluorite that gave off green light when heated, this was before UV lamps were around. So it appears that the daylight color is irrelevant to the definition.

Michael, thanks very much for that research & reply!! It would seem that chlorophane was know prior to 1832 or so. The chlorophane in our collection from the Barringer, the Badu, and the unnamed pegmatite near Inks Lake are all DARK purple (almost black) and the response to around 75 to 80 degreesC is blueish green. I haven't tried other temps....

SO, without complete analysis of the substance it would seem that the defining characteristics of chlorophane would simply a fluorite that is thermoluminescent or tribolumenescent - regardless of its non-excited color. The fluorescent reaction of Weardale material to sunlight would not move it into the chlorophane arena....

Don

Don,
It looks like all chlorophanes are reported as thermoluminescent green, while triboluminescence is reported for some common fluorites. Based on that, I would argue that green thermoluminescence is still the defining characteristic, with or without triboluminescence. The daylight color can be different.
Shall we vote?

Michael

That was easier than I thought...

This is not true. I have a piece I have repeatedly heated, maybe 6-10 times, I didn't really count, and it glows each time. But my piece is not from that locality.
Harold Moritz (2) Wrote:
-------------------------------------------------------
> Two points of caution, sunlight exposure destroys
> the fluorescence, so immediately put it in
> containers upon collection and keep it out of the
> light. Heating also destroys the fluorescence. So
> if you are going to heat a piece to demonstrate
> the thermoluminescence, use a piece you care to
> sacrifice. Once cooled, it will no longer
> fluoresce or thermoluminesce.

Well what ever the conclusion is about chlorophane, it should be added to Mindat's chlorophane page along with the references.

Rock Currier
Crystals not pistols.