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Mineral of the Month--January Fluorite Calcium Fluoride CaF2
Fluorite: A Global Quest for the Perfect Crystal by Ken Casey
Now, how does this apply to our purple fluorite specimens? Well, it is the play of
color that excites most students, scientists, and hobbyists. It seems as magic to
illuminate a fluorite cube with an invisible beam of light and observe a bright emanation
of dayglow colors; especially, if the emanating color is different from the
daylight color of ones specimen. Without its discovery, we would only marvel
at the myriad hues we observe in daylightif that is not enough! To proceed, let
us properly define our application of fluorescence. Fluorescence in minerals
is the result of bombarding the mineral with invisible ultra-violet light waves. This
releases visible light waves (photons) of different wave lengths (colors) from the
mineral.[xxv]
There are two major delineations of UV light for our model: longwave and shortwave.
A collector can purchase, borrow, or share a dedicated UV lamp that may one or two
outputs, covered by a purple glass, known as Woods glass. Each output will
produce either a longwave, or a shortwave light. A minerals fluorescence may
behave differently under each wavelength. Most simply, for
our purposes, [f]luorite fluoresces best under the long wave U. V. light. This
usually produces a blue light. In our long wave case the green fluorite fluoresces
blue.[xxvi] Many Fluorites fluoresce a
blue-violet color due to traces of europium; this is usually best under longwave UV.
Fluorite also fluoresces green, yellow, red, and white. Some will fluoresce one color
under short-wave, a second color under longwave, and even a third phosphorescence. Other
activators in Fluorite include Yttrium, Samarium, and some organic impurities.[xxvii] For example,
[f]luorite from Weardale fluoresces brightly purple while fluorite from Derbyshire
rarely fluoresces.[xxviii] Certain electrons in the
mineral absorb the energy from these sources and jump to a higher energy state. The
fluorescent light is emitted when those electrons jump down to a lower energy state and
emit a light of their own.[xxix]
Sometimes the fluorite will glow for several seconds after the UV lamp is turned
off. This bonus light is termed phosphorescence. With this
application we can further enjoy our perfect specimen! In
addition to discovering the cause of color, geologists have also linked the particular
impurities or trace elements to particular colors of light emitted by exposure to
ultraviolet light (fluorescence), and to certain associations with desired metal sulfide
ores to be mined commercially. In fact, a fluorides paragenesis (or conditions
of creation) can be linked to this effect. The fluorescent effects are gauged by
prospectors as indicators of the geochemistry of the minerals to be mined. When fluorite
is not the desired mineral to be mined in commercial quantities, even as a gangue mineral
can be used as clue to the presence of desired metal sulfide ores. [G]angue
and ore minerals in many instances are genetically related. For example, the
presence of a dark purple fluorite may indicate the availability of uranium, lead, or zinc
ore bodies nearby.[xxx] Two Russian
mineralogists, Ganzeyev and Sotskov, stated in a 1976 article on the composition of their
native fluorites that: Overall, the trace REE's encountered in the highest
concentrations were ytterbium (Yb), cerium (Ce), samarium (Sm), and lanthanum (La), in
that order. Also found in fluorite were europium, terbium, lutetium, and strontium (not a
REE, but tested for anyway).[xxxi] And that
the amounts of trace REE's
corresponded with the conditions under which the fluorite crystallized.[xxxii] Quarries in our area that have purple Fluorite Though our
clubs interest leads us more toward the collection of crystal specimens, rather than
the raw geology that has created them, a basic understanding of the natural processes that
govern their formation can aid us in prospecting for the finest specimens. For
example, by finding even a bit of massive purple fluorite running in a vein of white
calcite from a southeastern Pennsylvania limestone quarry, we can ascertain that a
possible association of other desirable minerals could be close by. Various pink and
white dolomite saddles, multi-faceted clear calcite crystals, and even some cubes of
pyrite perched upon the two could be the vug-find of the day, if one searches with
aplomb. As a matter of
fact, we discovered a bonanza of such finds at our November 20, 2004 fieldtrip to Kurtz
Quarry in Denver, PA. Bob, Karissa, Joe, John, Tim, Guy and Wendy reaped the
benefits of a basic geologic knowledge of the quarry. Eric and Jake found the nicest
pyrite/calcite vein Ive seen in awhile!
Other Pennsylvania quarries offer similar possibilities. In 2004, we have visited a
few: the Kurtz Quarry in Denver, the
Binkley-Ober Quarry in East
Petersburg, PA, Meckleys Quarry
in Mandata, and a NEFTA trip to Doylestown, PA.
Known locations of others are: Oak Hall Quarry, College Township, PA and the Ormrod
Quarries of Heidelberg Cement. Our VP of Fieldtrips, Bob Asreen, is working to setup
an excursion to Martin Limestones Burkholder Quarry in Lancaster County. The Nittany Mineralogical Society has reported finds of
some handsome fluorites there. This is just in our own backyard! Crystallography
Fluorite shares
a common, visible crystal structure with such minerals as Pyrite. It
crystallizes in the Isometric System and usually forms cubes, octahedrons (less likely),
and rarely dodecahedrons (12-sided figures). Often nature combines the forms into
twinned, interpenetrating cubes, or cubes with their corners modified. One could
speculate that since iron pyrite (FeS2) forms cubes like our predominantly
purple fluorite (with trace amounts of iron oxide) that fluorites tendency toward
forming cubes in our local area would be worthy of investigation. For more on Fluorite, see: http://www.mindat.org/min-1576.html. On recent
fieldtrips, we have found mainly purple cubes, measuring about 1-5 mm. It is
possible, that upon future adventures, we will come across larger, green cubes for
sampling. Once You Have Them
One you have
them, what next? Well, there are many means of enjoying and sharing your most
excellent specimen of fluorite. The first thing is to prepare your crystals for
viewing. That is best done with a very soft-haired brush, as fluorite scratches
easily (Mohs Hardness Scale
of 4). Though insoluble in water at temperatures collectors use, brushing with water
can dull the luster of the crystal faces, Im told by fellow collectors. Or,
soak them in water and dish soap for a few days.[xxxiii]
The use of acids is ill advised. Next, its
up to you. You can display it at home, show it at our next club meeting, or junior
members and teachers could show it as an educational tool. Trading or selling your
specimen is entirely up to you. And, if you deem yourself generous enough to give it
away or donate to a school or museum, you reap the intrinsic rewards of sharing. Some folks go
one step further, and process their finds into stonework or jewelry, using lapidary
techniques. Being relatively soft, fluorite takes shaping and polishing easy enough.
Though somewhat fragile, it makes for brilliant cut stones, vases and vessels,
spheres, and most popularly today, beads. Once you have collected the perfect specimen of fluorite, you may never go back to the ordinary, less colored and less-photoactive minerals. Thanks for joining me on our adventure. If you are in the neighborhood, drop by one of our meetings to discuss this article and more. (We meet the second Monday of every month, except July and August.) Until we can meet upon the frozen shores of Antarctica, Happy Rockhounding to you on every continent.
Links
Museums & Galleries
World Famous Locales
UK
Illinois State Geological Survey
Geobit 4: FluoriteIllinois State Mineral, November 7, 2003, ISGS.
January 5, 2005 Wright, C. L., and Rakovan, J. COLOR, ITS CAUSE, AND RELATION
TO REE CHEMISTRY AND Miller, Benjamin L. Lehigh County
Pennsylvania Geology & Geography, Fourth Series Bulletin C39. Pennsylvania Department
of Internal Affairs, Topographic and Geologic Survey: 1941. Lehigh University
Digital Library, PA. 2 Jan. 2005 Aber, Susan Ward Course
Lecture: GO 340 Gemstones & Gemology: Visual Properties. Hurlbut, Jr., Cornelius, and Klein,
Cornelis, Manual of Mineralogy (after James D. Dana), 19th Bean, Rachel Course Lab: Geology
202a: Mineralogy: Lab 3: Mineral Colors. Bowdoin College. Deer, W. A., Howie, R. A., and
Zussman, J. An Introduction to the Rock Forming Minerals. Hagemann, Steffen Geology 364:
Ore Genesis Lecture Notes: Hydrothermal Alteration Barnes, John H. Rocks and Minerals
of Pennsylvania, Education Series 1, 4th series. Read, Stephen E., Cooper, Alan F., and Walker, Nicholas W.
Geochemistry and U-Pb Rocks and Minerals of
Kentucky: Fluorite. Kentucky Geological Survey, University of Fluorite Mining.
Illinois State Historical Society, Springfield, IL. 4 Jan. 2005 Specimen #M255. Mt. Lily Gems,
Burnsville, NC. BERTELLE, M., LEOTTA G., CALOGERO,
S., Universitą di Venezia, Venezia, Italy; Eastern Minerals Team. "USGS
Fact Sheet: MRDS Quarterly Reports: Commodity Inventory Ward, Paul. Cool Antarctica:
Human Impacts on Antarctica and Threats to the Environment - Leach, David. Sediment-hosted
base-metal deposits. U. S. Geological Survey, USGS Jolyon, Ralph. Fluorite.
Mindat.orgThe Mineral Database. Croydon, Surrey, London, Gem & Mineral Miners, Inc.
Fluorite: Mineral Information Page. 14 Jan. 2001. 2 Jan. 2005 Abramowitz, Mortimer (Oympus
America, Inc.), Johnson, Ian D., Parry-Hill, Matthew J.,Flynn, Cross, Bob. Fluorescence in
Minerals
. San Jacinto College. 3 Jan. 2005 Fluorescence in
Minerals. Minershop.com. 30 Dec. 2004 Macolm, Gavin. Mineral
Gallery: Fluorescence in Minerals. UK: The Russell Society, 2003. Amethyst Galleries, Inc. The
Fluorescent Minerals. 2002. 28 Dec. 2004 Thorsten, Christian.
CR-Scientific Minerals & Earth Science newsletter, HTML archive Rylands, C. J. P. The Rock
Candy Mine: Plates of Fluorite, Barite and Quartz!. 1997. Photo, Graphic & Literary Credits With our grateful thanks to: Dick Nelson (c/o IC Minerals) © 2005 All contributions to this
article are covered under the copyright protection of this article Reproduction of this article must be
obtained by express written permission of the author, [i]
Illinois State Geological Survey Geobit 4: FluoriteIllinois State
Mineral, [ii] C. L. Wright and
J. Rakovan, COLOR, ITS CAUSE, AND RELATION TO REE [iii]
Benjamin L. Miller, Lehigh County Pennsylvania Geology & Geography, Fourth [iv]Susan
Ward Aber, Course Lecture: GO 340 Gemstones & Gemology: Visual [v]
Cornelius Hurlbut, Jr. and Cornelis Klein, Manual of Mineralogy (after James D. [vi]
Rachel Bean,Course Lab: Geology 202a: Mineralogy: Lab 3: Mineral Colors. [vii]
W. A. Deer, R. A. Howie, and J. Zussman, An Introduction to the Rock Forming [viii]
Steffen Hagemann, Geology 364: Ore Genesis Lecture Notes: Hydrothermal [ix]
John H. Barnes, Rocks and Minerals of Pennsylvania, Education Series 1, [x] Miller, p. 449. [xi] Stephen E.
Read, Alan F. Cooper, and Nicholas W. Walker, Geochemistry [xii] Rocks and Minerals of Kentucky: Fluorite. Kentucky Geological
Survey, [xiii] ISGS, 7 Nov. 2003. [xiv] Fluorite Mining. Illinois State Historical Society,
Springfield, IL. 4 Jan. 2005 [xv] Specimen #M255. Mt. Lily Gems, Burnsville, NC. [xvi] M. BERTELLE, G. LEOTTA, S. CALOGERO, Universitą di Venezia, Venezia, [xvii] Eastern
Minerals Team, USGS Fact Sheets: MRDS Quarterly Reports:
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November Mineral of the Month: Stilbite | |||
October Mineral of the Month: Celestite | |||
Members, Want to see your name in print? Want to co-author, contribute, or author a whole Mineral of the Month article? Well, this the forum for you! And Members, if you have pictures, or a story you would like to share, please feel free to offer. We'd like to post them for our mutual enjoyment. Of course, you get full photo and author credit, and a chance to reach other collectors, hobbyists, and scientists. We only ask that you check your facts, give credit where it is due, keep it wholesome for our Junior Members watching, and keep on topic regarding rockhounding. You don't even have to be experienced in making a webpage. We can work together to publish your story. A handwritten short story with a Polaroid will do. If you do fancier, a text document with a digital photo will suit, as well. Sharing is the groundwork from which we can get your story out there. Our club's webpages can reach any person surfing the net in the world, and even on the International Space Station, if they have a mind to view our website! We are hoping for a possible tie-in to other informative programs upon which our fellow members might want to collaborate. Contact any officer or board member with your suggestions. For February or March 2005, we are looking for contributors on "Agate", to tie-in with this year's March Show theme: "The World of Agates." ____________________________________ All of the Mineral of the Month selections have come from most recent club fieldtrips, thus far. If you have a suggestion for a future Mineral of the Month, please e-mail me at: kencasey98@yahoo.com, or tell me at our next meeting.
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Photos
by: Dick Nelson, Isaias Casanova, Eric Greene, Chris Thorsten, Karissa Hendershot, Ken
Casey, NSF, NGS
Drawings by: Ken Casey
Article and content contributed by permission of author(s) © 2004-5.
This page last updated: February 19, 2011 10:14:43 AM
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