Learning is an everyday event for a slummer like
me. For example, take the element
cerium! Before today, what did I know
about cerium? Turns out not much. I knew that: it was named after the dwarf
planet Ceres; 2) cerium oxide is used in polishing high quality glass lenses,
and as a final polish for some lapidary specimens; 3) it is “probably” a Rare
Earth Mineral (REE); and 4) somehow it is used in gas (the lantern gas, like
Coleman) mantles. Other than those
factoids my knowledge about cerium was pretty sparse.
OK, Ceres is the largest planet, or “object” that is
positioned between Mars and Jupiter in the asteroid belt (that factoid came
from my early 1960s era astronomy class).
In turn, Ceres was named after the Roman Goddess of agriculture and fertility.
Cerium oxide is both unstable Ce2O3
and stable CeO2 and the latter is often referred to as cerium(IV)
oxide and is the type used in polishing compounds.
Cerium is a lanthanide element—one of the 15 metallic
elements with atomic numbers 57-71. This
group also contains elements not overly familiar to non-chemists such as
neodymium and europium.
Pretty amazing to me is that cerium is much more
abundant in the earth’s crust than lead or tin and despite the REE moniker is
not very rare. As for lantern mantles, I
fail to understand the chemistry but mixing thorium oxide with cerium oxide and
coating the silk mantles produces a very white light. I suppose today very few “younger persons”
know how to properly install a mantle in a “gas lantern!” Of course, as a kid I knew next to nothing
about burning whale blubber oil but did know how to “trim a wick” in a kerosene
lamp!
I have learned that in nature cerium seems to never
occur as a stand- alone element and that most cerium is produced from mining
and refining the
Rare Earth Minerals monazite (cerium + lanthanum + REE + thorium + PO4) and bastnäsite (REE + cerium carbonate fluoride). I have a couple of specimens of the above minerals but was surprised to see a specimen of the REM parisite offered for two bucks at a mineral store in Tucson. I did not have the slightest idea what parisite was when I found the specimen in an isolated drawer of thumbnails. But due to what Phillip Caputo (2013) calls the MD (Magic Droid), I soon learned much and for that low price will pick up most anything that is not in my collection!
Rare Earth Minerals monazite (cerium + lanthanum + REE + thorium + PO4) and bastnäsite (REE + cerium carbonate fluoride). I have a couple of specimens of the above minerals but was surprised to see a specimen of the REM parisite offered for two bucks at a mineral store in Tucson. I did not have the slightest idea what parisite was when I found the specimen in an isolated drawer of thumbnails. But due to what Phillip Caputo (2013) calls the MD (Magic Droid), I soon learned much and for that low price will pick up most anything that is not in my collection!
So, parisite is a rare-earth carbonate with fluorine, or Ca(REE)2(CO3)3F2. Well, that last statement is sort of a
generality because mineralogists “in the know,” and with an XRD or some other
gizmo providing analytical information, use parisite as a general term and designate
the minerals parisite-(Ce), parisite-(Nd) and parisite-(La) depending on the
“domination” of these REE. And then it
becomes quite easy to confuse parisite (any type) with lanthanum-dominant
specimens of bastnäsite, synchysite, and röntgenite,
And, so its goes.
Photomicrograph of a banged-up and chipped parisite crystal. Note partial hexagonal faces at arrow. Height of crystal ~1.3 cm. |
Therefore, the question then becomes, what is the correct name for my
purchased specimen. I am going to settle
on parisite-(Ce) [CaCe2(CO3)3F2],
not because I have a XRD in my back pocket, but because MinDat has stated the
cerium variety is the mineral species at the Snowbird Mine in Montana, the home
of my small collected crystal.
Parisite is not what one would call a spectacular mineral, nor a museum
piece, but one that is mainly of interest to rockhounds. It seems only to occur as definite crystals
and not as massive or encrusting forms.
Parisite belongs to the Hexagonal Crystal System and commonly occurs as
double hexagonal pyramids that at times appear to be prismatic. However, the crystals are not prime specimens
and often are striated and very “rough” looking. Crystals are often brown or amber in color
but at times range down to brownish-yellow to yellow. Specimens are very brittle, are
transparent to translucent with a yellow-white streak, and have a sub-vitreous
to greasy luster. Hardness has been
measured as ~4.5 (Mohs). Almost all
crystals are small in size and I suppose 3 cm. would represent a very large
specimen.
Metz and others (1985) describe the Snowbird Mine as occurring in “a
lenticular, rare earth- and fluorite-rich quartz-carbonate body with a
pegmatitic texture, which intrudes Belt Supergroup metasediments [late
Precambrian] at the Idaho-Montana state line west of Missoula, Montana…the
U-Th-Pb parisite ages (71.1 + or - 1.0 m.y.) indicate emplacement during the
Late Cretaceous, probably associated with the intrusion of the nearby Idaho
batholith.”
REFERENCES CITED
Metz, M.C., D.G. Brookins, P.E. Rosenberg and R.E. Zartman, 1985, Geology
and geochemistry of the Snowbird Deposit, Mineral County, Montana: Economic
Geology, vol. 80 no. 2.
Caputo, P., 2013, The longest road: overland in search of America from
Key West to the Arctic Ocean: Henry Holt and Company, New York.
I had only one hard-and-fast
rule: avoid interstates. They are predictable and boring and their uniformity
somehow erases changes in landscape; you can drive six hundred miles, from forests
into deserts, and feel that you haven’t gone anywhere. In a sense, you haven’t. You have no idea about the lives of the
people in the towns and cities you’ve bypassed at seventy miles an hour. Phillip Caputo
No comments:
Post a Comment