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| Mineralia 2011 |
An intransitive verb is an
action verb, for example, suffer. But if
you stick an object with an action verb then the verb becomes transitive. A good
example is Mike suffers (verb) pain (object) in the lumbar region of
his lower back.
The dictionary tells me that pain is a basic bodily sensation induced by a noxious stimulus,
received by naked nerve endings, characterized by physical discomfort.
Yep, I can agree about the pain. A condition called
spinal stenosis is physical discomfort caused by narrowing of the lumbar spinal
column that produces pressure on the nerve roots resulting in sciatica and a
condition resembling intermittent claudication and that usually occurs in
middle or old age. That is correct---it hurts to get old.
But, in today’s world there might be an opportunity to
“fix” the stenosis and so it was I decided to undergo a bilateral lumbar
laminectomy. This procedure removed the
back part (lamina) of the affected vertebra (L 2-4 in my case). A laminectomy
is sometimes called decompression surgery because it eases the pressure on the
nerves by creating more space around them.
And the leg pain sort of disappeared. In on Thursday out on Friday noon with nary a
narcotic “pain killer” down my gullet after dismissal. But there is the LBT—no lifting, bending, or
twisting for several weeks. Shucks, I
can’t mow the lawn, shovel snow or lift a large bag of taters. However, a simple twist yesterday just about sent me through the roof.
But, the state of being weary and restless through
lack of interest, also known as boredom, has struck. It might not have stayed except a giant back
brace (24/7 for 6 weeks) makes my desk chair rather uncomfortable.
So, time to bite the bullet. Bite it really hard since I dug out a box of
specimens from the Ojuela Mine (Mexico) tucked away marked "arsenates" but containing
little other information. I had picked
these up from a dealer at Tucson a couple of years ago and had stuck them in
the “To Do” box. So out they came, and a
couple were really tough to decipher for an ole soft rock person.
The Ojuela Mine in the Mapimi District, Durango,
Mexico, is a polymetallic mine (mostly gold, lead, silver, zinc) with mineral formation in Mesozoic
carbonates. Although the mine produced a
variety of metallic ores, it is best known for other reasons: 1) Santiago Minguin,
the designer of the Golden Gate Bridge, executed the design and construction of
a suspension bridge to the mine that is 1043 feet in length and anchored by two
end towers; 2) beginning in the 1940s specimen mining started producing magnificent
examples of adamite, paradamite, scorodite
and hemimorphite---some of the best in the world. The mine has produced over 100 different
minerals and is the type locality for six minerals.
It seems to be especially rich in arsenate minerals.
So, on to my specimens. One was a piece (~4.5 x 8.0
cm) of limonite/goethite with several beautiful, butterscotch-colored, blocky
crystals of the lead molybdate, wulfenite, perched on the surface. This was an easy one to identify, although it
was not an arsenate. Shucks.
Really nice blocky crystals of wulfenite on goethite/limonite. FOV both ~3.3 cm.
The next jewel in the box (~3.0 x 3.5 cm) indeed was a calcium
copper arsenate, conichalcite (with nice “little green balls), CaCu(AsO4)(OH).
Green conichalcite spherulites; submillimeter in diameter.
Another two specimens (~1.7 x 1.0 cm and ~2.0
x 2.0 cm) took some sleuthing and I am not yet certain about the identification,
but both are arsenates. However, my
guess is: 1) arsenbrackebuschite, a lead iron arsenate;
and 2) the lead zinc arsenate, tsumcorite. Both are “microminerals.”
Arsenbrackebuschite
is a real tongue twister. According to MinDat.0rg
the name originated with the lead manganese vanadate mineral, brackebuschite [Pb2Mn3+(VO4)2(OH)]. That mineral, in turn, was named for the
German mineralogist Luis Brackebuschite.
In arsenbrackebuschite the arsenate ion replaces the VO4 [Pb2Fe3+(AsO4)2(OH)]
and iron replaces the manganese.
Arsenbrackebuschite is
a rather uncommon mineral found in the secondary (oxide) zone of arsenic-bearing,
hydrothermal lead-iron deposits. The
co-type localities are at the Tsumeb Mine in Namibia and the Clara Mine in Germany.
The polymetallic mines at Mapimi have
produced my specimens. In contacting the
dealer at a later date, I was informed that the tiny, poorly formed crystals
had been identified by XRD and confirmed my visual identifications. But the mineral is rare at the Ojuela Mine.
Arsenbrackebuschite is yellow to amber to red brown in
color with some well-formed crystals having a shiny (sub-vitreous) to waxy
luster while mine are more earthy, maybe resinous--and very tiny and indistinct. Some better formed crystals have a hardness
of ~4.5 (Mohs) although it would seem impossible to measure the earthy variety.
It is a tough mineral to identify as even mineral photos on MinDat.org are
measured in millimeters.
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Photomicrograph of poorly formed, yellow-amber, submillimeter crystals of arsenbrackebuschite. The total width FOV is ~6 mm.
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If arsenbrackebuschite is
tough to identify then a hydrated lead zinc arsenate, tsumcorite,
is even more difficult. Here the mineral
has replaced the iron with zinc: PbZn2(AsO4)2-2H2O. Note that OH in arsenbrackebuschite is
replaced by 2 water molecules in tsumcorite.
My chemistry is at an elementary level, but I believe that since the iron
has a 3+ charge and zinc a 2+ charge then in order to balance charges it picks
up an extra hydrogen. I could really use
some help from a reader more learned in chemistry!
I have identified these clove-brown, microscopic crystals as tsumcorite. Width field of view ~11 mm.
Elongated, along C-Axis, double pyramids of submillimeter, light yellow wulfenite crystals.
The type locality for tsumcorite is the Tsumeb Mine in
Namibia and, in fact, the name comes from the mine owner—Tsumeb Corporation. Again, this is one of those rare arsenates that
is found in the oxide zone of arsenic-bearing, hydrothermal, polymetallic mines.
It ranges from yellow-brown, clove brown, red-brown, or orange in color. The tiny crystals are generally prismatic and
elongated along the B-Axis, not the C-axis. These prismatic crystals often occurring
in radiating spherules. The hardness is
~4.5 (Mohs). How did I identify these
ting crystals? I broke off a couple and obtained a yellow streak (I
think). Minerals with a yellow streak
are rare. They also dissolved in
hydrochloric acid. Otherwise is was a
wild guess.
Another non-arsenate mineral that popped up in the
Ojuela specimens was chalcophanite, a hydrated, zinc-iron-manganese,
manganese oxide [(Zn,Fe,Mn)Mn3)7-3H2O]. Again, chalcophanite is a common oxide
mineral in polymetallic deposits.
However, it often is difficult to visually (as are many manganese
minerals) identify since individual crystals are quite small. Crystals are often platey,
soft (~2.5 Mohs), metallic opaque with a color ranging from dark blue to black.
These tiny crystals often form a druse-like coating.
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"Clumps" of chalcophanite with green spherules of conichalcite? Width FOV ~11 mm.
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Perhaps the most beautiful specimen (~10 x 6 cm.) in
my mixed box is a combination of gemmy hemimorphite crystals of all sizes and shapes scattered
over a chalcophanite matrix. Hemimorphite
is a hydrated zinc silicate [Zn4Si2O7(OH)2-H2O]
that occurs in a number of environments, colors, lusters, and for decades was
confused with the zinc carbonate, smithsonite [ZnCO3]. The name comes from doubly terminated crystals
where the terminations have different faces (hemimorphic development). The crystals have a white streak, a vitreous
luster, ~5 hardness (Mohs), are colorless and transparent to translucent, and
come from the oxidized zone of zinc-bearing mineral deposits. With a zinc component
of over 50%, hemimorphite is a minor ore of zinc.
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Gemmy crystals of hemimorphite scattered on a matrix of chalcophanite with a base of goethite/limonite.
In a photomicrograph these submillimeter "white" acicular crystals are scattered over the chalcophanite.
On the reverse of the above specimen there is a vug filled spherules of the copper zinc carbonate, rosasite [(Cu,Zn)2(CO3)(OH)2
]. Length of vug ~1 cm.
Also on the reverse is another mineral. A wild guess is scorodite, an iron arsenate [Fe3+AsO4 · 2H2O].
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The question, at least one of them, is the identity of
some really microscopic mineral aggregates situated on the spherules of chalcophanite. At one time or another I thought perhaps cerussite,
hemimorphite, pyrolusite (but needles are not black), ojuelaite, and perhaps
others. It is a tough call and above my
pay grade to make it!
I learned much from this little exercise, not the
least of which is that submillimeter crystals are very difficult to photograph
with my digital camera. The second is
that many arsenates have been discovered in the last 50 years and are relatively uncommon. The third, life is good: learn to enjoy every minute of
your life. Be happy now. Don't wait for something outside of yourself to make
you happy in the future. Think how really precious is the time you have to
spend, whether it's at work or with your family. Every minute should be enjoyed
and savored.
Earl Nightingale
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