Creedite (light purple) from the Cresson Pit, Cripple
Creek Mining District. Width of photo ~5
cm.
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Creedite [Ca3SO4Al2F8(OH)2-2H20]
is a rather uncommon, hydroxyhalide mineral (minerals with a Halide Group
anion—chlorine, fluorine, bromine, iodine--- plus the hydroxide radical) that
has a Colorado mine as its type locality.
Creedite is often the result of fluorite oxidation so it is not
surprising that the mineral was first discovered (1916) and described from the fluorite
mine at Wheel Gap near Creede, Colorado; hence, it picked up its name from the
topographic quadrangle. The creedite crystals are found in a fluorite-barite
vein in a Tertiary lava flow intermixed with tuffs of predominantly rhyolitic
and quartz latitic composition (Eckel and others, 1997).
Most creedite specimens that I have seen occur as
acicular, prismatic and radiating crystals although some are granular
aggregates while others form as druses (Monoclinic Crystal System). The most
colorful of the specimens are purple to violet or orange in color although many
are colorless to white; some blades are included with various minerals. The
acicular crystals are vitreous and transparent to translucent and all have a
white streak and are quite brittle.
Crystals are fairly soft but determining that property is somewhat difficult
(~4.0 Mohs). Creedite seems restricted
to areas where hydrothermal solutions were rich in fluorine and later oxidation
of fluorite produced the mineral. I
could not locate information on the “coloring” of creedite. However, I presume it is allochromatic and
small amounts of impurities will impart the color.
Above three photomicrographs are of clear acicular
crystals of creedite from the Navidad Mine.
Width of photomicrograph ~ 1.4 cm.
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Mass of radiating creedite crystals from Navidad Mine.
Width of photomicrograph ~2.5 cm.
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I have two creedite specimens marked Navidad Mine,
Abasolo, Rodeo, Mun. de Rodeo, Durango, Mexico, and two more specimens
collected from the Rodeo Mine in the same general vicinity. In fact, MinDat.com indicates that the
correct location name is the Navidad Mine and “Mina Abasolo” and “Mina Rodeo”
are “misnomers derived from the nearest village and municipality.” The mine(s) produce large quantities of
industrial-grade fluorite derived from a fluorine-rich hydrothermal
solution. After the formation of the
fluorite into veins the area was faulted and brecciated and some created vugs
then held the peach-orange, radial groups of creedite (Megaw, 2013). At times a cube or two of fluorite are
intermixed with the creedite blades and some sort of an orange-peach clay
mineral actually held the creedite groupings and at times is included within
the creedite crystals.
I also have a beautiful cluster of light purple,
prismatic creedite crystals surrounded by black botryoidal goethite from the
famous mines at Santa Eulalia District, Mun. de Aquiles Serdán, Chihuahua,
Mexico. Unlike the Navidad mines, the
Santa Eulalia mines were sulfide producers: lead, zinc and silver with minor
tin and copper and a few others. Also
unlike Navidad, Santa Eulalia minerals are the result of
dissolution-precipitation in host Cretaceous limestone beds or skarns
(Carbonate Replacement Body) with fluids from nearby Tertiary intrusive rocks. The several stages of fluorite depositional
events produce a variety of crystal shapes and colors. The creedite then is a result of later
oxidation, by meteoric waters, of the fluorite.
Santa Eulalia has been one of Mexico’s chief producers of silver, lead
and zinc. Above from Megaw, 1990.
The most interesting specimen of creedite in my
collection was picked up at the recent Pikes Peak Gem and Mineral Show. Although creedite was first discovered/named
from a Colorado mine, the mineral is not all that common in mines of the
state. In fact, the 1997 edition of Minerals
of Colorado (Eckel and others) did not list a single locality for creedite
other than the original discovery site.
Therefore, it was of great interest that in 2001several creedite
specimens were found in the Cresson Pit near Victor in the Cripple Creek Mining
District. From what I understand, a Colorado mineral dealer was able to obtain
much/most of the limited supply and offered specimens for sale at the 2003
Denver Show. I was not living in
Colorado at that time but have not seen Cripple Creek creedite for sale at
other shows; therefore, I was happy to obtain this specimen. Carnein and Bartos
(2005) and Cook (2008) described the Cripple Creek occurrence in the Mineralogical Record and Rocks and Minerals: “Specimens consisted
of radiating groups of colorless/white, bluish-purple, lavender, and
pinkish-purple crystals to 1 cm associated with blue, white, and yellow
celestine, botryoidal pink rhodochrosite, gearksutite, and pyrite.”
The specimen in my collection has nice sprays of
mostly light purple to clear crystals of creedite, very tiny cubes of scattered
pyrite, white massive gearksutite, a few micro cubes of clear fluorite, perhaps
some tiny white crude crystals of celestine, and perhaps other minerals including
barite. However, I could not locate
rhodochrosite as noted in the original find and description.
Very nice examples (G) of the alumino-fluoride
gearksutite. Width of photomicrographs ~7mm.
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The most interesting mineral, other than the creedite,
is gearksutite, a fairly rare hydroxyhalide—a complex alumino-fluoride:
Ca[Al(F,OH)5(H2O)].
Most descriptions of gearksutite describe it as being a dull, earthy,
white-looking, soft (2.0 Mohs) chalk-like mineral often forming nodules. However, 1) under SEM magnification the
mineral is composed of minute fibers that actually are lath-shaped crystals
(Mineral Data Publishing, 2016); 2) it also occurs as minute, vitreous
crystalline “balls” that sometimes show radiating crystals.
Submillimeter crystals of “something”, per celestine (C?) along with
tiny cubes of pyrite (P). Width of
photomicrograph ~7 mm.
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Possible celestine (C?) along with botryoidal gearksutite
(G?). Width photomicrograph ~7 mm.
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The unknown (?B) mineral. It seems bladed or platy sort of like
barite. Width photomicrograph ~7mm.
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As best that I can determine (information below from
MinDat.com), gearksutite forms: 1) as an alteration product of cryolite [Na3(AlF6)]
or pachnolite [NaCa(AlF6)-H2O] or fluorite [CaF2];
2) from low temperature, late stage hydrothermal solutions rich in fluorine; 3)
as “wall rock” alteration, at the type locality; 4) from slag rich in halogens
at some locations in Austria; 5) from an alumino-fluoride breccia pipe in Virginia;
6) replacing an elpasolite [NaK2(AlF6)] + weberite [Na2Mg(AlF6)F]
mixture which was a replacement product of primary prosopite [CaAl2(F,OH)8];
and in Kazakhstan, 7) during interaction of HF (produced by pyrite oxidation in
fluorite matrix) with concretions of [of the aluminum clay minerals] allophane
or caoline [kaolinite].
What all this indicates to me is that gearksutite is a
late stage mineral that can form in a number of fluorine-rich environments, is
fairly rare and tough to identify, and whose actual mode of formation is way
above my pay grade. Never-the-less, I am
happy to have acquired the specimen.
I thank Professor Bob Carnein (a real mineralogist) from
the Lake George Gem and Mineral Club for his information about the Cresson Pit specimens.
Additional information about some aspects of the Cresson Pit appear in
an October 2014 Posting on the Carlton Tunnel and December 2015 Posting on
Cripple Creek Scripophily. And, Cook (2008)
pointed out that in “summer 2007, narrow vugs lined with small colorless to pale
purple creedite crystals were found in the Henderson molybdenum mine, Clear
Creek County” Colorado.
REFERENCES
CITED
Carnein, C. R., and P. J. Bartos, 2005. The Cripple
Creek mining district, Colorado: Mineralogical Record v. 36.
Cook, R.B., 2008, Creedite: Cresson Mine, Cripple
Creek Teller County, Colorado: Rocks & Minerals v. 83, issue 5.
Megaw, P.K.M., 2013, Mexican Fluorite: Rocks and Minerals, v. 88, issue 2.
Megaw, P.K.M., 1990, Geology and geochemistry of the
Santa Eulalia mining district, Chihuahua, Mexico: Ph.D. Dissertation, The
University of Arizona.
Mineral Data Publishing, 2016, Gearksutite: www.HandbookofMineralogy.com.
I
write to understand my circumstances, to sort out the confusion of reality, to
exorcise my demons. But most of all, I write because I love it!
Isabel Allende
Isabel Allende
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