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Minerals Featured in 2011
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Scolecite, Sangamner, Ahmadnagar District, Maharashtra, India |
January 2011 Scolecite from India. This month’s mineral is an uncommon
zeolite group mineral from India that can forms delicate, lovely,
colorless-to-white blades, as seen in the photo to the left. These long,
thin crystals are an external manifestation of the internal structure of the
long, aluminosilicate chains that comprise scolecite, as our write-up
discusses. It also explains scolecite's origin as a secondary mineral in
volcanic host rocks, the difficulty of collecting this fragile mineral, the
unusual properties of the zeolite-group minerals, and why mineralogists
recently revised the system of zeolite classification and nomenclature.
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February 2011 Azurite from Arizona.
We're very excited about this month!
We're featuring azurite, a colorful, hydrous copper carbonate from Arizona’s
famed Morenci Mine. Our write-up explains azurite’s mineralogy, its use as
both an ornamental stone and an early ore of copper, and the history and
technological development of one of the world’s greatest copper mines.
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Azurite, Morenci Mine. Morenci, Greenlee County, Arizona |
Axinite-(Fe), New Melones Lake near Copperopolis, Calaveras County,
California. Two Gold-level specimens shown here.  |
MARCH 2011 AXINITE-(FE) from California. The September-October
1982 issue of the Mineralogical Record contained an article on a new
find, stating: "In the fall of 1981, very fine Ferroaxinite specimens
were collected from the spillway adjacent to New Melones Lake near
Copperopolis in Calaveras county. Since its discovery, this locality has
produced some of the finest ferroaxinite specimens ever found in North
America." We are delighted to have obtained a nice lot from this find!
(The name of the mineral has been changed from Ferroaxinite to
Axinite-(Fe) in the intervening years.) Gold-level specimens are much
smaller than usual--small crystals on small matrix, most about 1" to 2".
We're mounting the smaller pieces on the Acrylic squares we offer, which
makes then much showier. |
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APRIL 2011 KYANITE from Brazil. Our kyanite specimens
were collected at the Capelinha Mine near Capelinha in the Jequitinhonha
Valley in the Brazilian state of Minas Gerais, which is one of the
world’s premier sources of mineral crystals and gemstones. Our specimens
were obtained as a by-product of mining pegmatite gemstones. In the
early Paleozoic Era some 490 million years ago, the present-day surface
of Minas Gerais was buried to a depth of about 12,000 feet. The basement
rock, which consisted of highly metamorphosed gneiss, schist, and
quartzite, was intruded by granitic magma that created gemstone-bearing
pegmatites and provided the pressures that formed our kyanite crystals
in the adjacent schist. Capelinha has three pegmatite gemstone mines,
the Capelinha, Campo do Boa and Fazenda Rubin Pimenta mines, which are
worked by both open-pit and underground methods. These mines yield
crystals of topaz, titanite, and the tourmaline mineral elbaite. In
their search for gemstones, pegmatite miners remove large quantities of
surrounding schist, which sometimes contains well-developed, blue
kyanite crystals. This is just a portion of what you will read in this
month's write-up! |
Kyanite, Capelinha Mine, Jequitinhonha Valley, Minas
Gerais, Brazil |
Rhodonite, San Martín Mine, Huallanca
Bolognesi Province, Ancash Department, Peru We
were very excited about the gorgeous
specimens we will be sending you in May! And we are not
exaggerating--the May-June 2007 Mineralogical Record calls these
"Gorgeously deep pink aggregates of bladed rhodonite crystals." Since
these are exceptional, gorgeous, and rare, they are especially
valuable--and as a result, our specimens on all levels were
significantly smaller than usual. |
MAY 2011 RHODONITE Our rhodonite specimens
were collected at the San Martín Mine at Chiurucu, Huallanca District,
Bolognesi Province, Ancash Department, Peru. Huallanca District, with an
average elevation of 6,000 feet and covering 337 square miles, is 80
miles east of the Pacific Coast and 125 miles north-northeast of the
national capital of Lima. Local mineralization was emplaced following
the crustal fracturing that accompanied the uplift of the Andes some 60
million years ago. Mineral-rich, hydrothermal solutions surged upward in
multiple phases into fractures within quartz-monzonite and granitic
country rock to precipitate an array of minerals in complex vein
systems. Both the Incas and the colonial Spanish mined silver at
Huallanca. Zinc mining became prominent at Huallanca in the 1960s when
several underground mines were developed, including the San Martín Mine,
a small, multi-metal operation that produces zinc and lesser amounts of
silver, lead, and copper. Crystals of rhodonite, a gangue mineral at the
San Martín Mine, gained popularity with collectors in the early 1990s.
Miners found major rhodonite pockets in 1991, 1995, and 1997, and again
in 2007 when our specimens were collected. The San Martín Mine has since
closed and is unlikely to reopen. The write-up we will be sending along
with the beautiful rhodonite specimens contains much additional
information, including a special section on "Decorative Stones" like
rhodonite. |
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JUNE 2011
AEGIRINE Our specimens were collected at a recently recognized,
classic locality for aegirine—Zomba Mountain in the Chilwa Alkaline
Province in the Zomba District of the Southern Region of the
southeastern African nation of Malawi. The origin of our specimens is
linked to the formation of the East African Rift System, a series of
long, narrow, north-south-oriented depressions in the Earth’s surface
and Africa’s most prominent geological feature. When the rift began to
form some 65 million years ago, crustal fracturing was accompanied by
the emplacement of numerous igneous intrusions and widespread extrusive
(volcanic) activity. At present-day Zomba, Malawi, these intrusions
consisted of nepheline syenite, a granite-like, igneous rock that
solidified from alkaline (silica-poor) magma. The final sections of
these intrusions to solidify were zones of residual magma that were
enriched with quartz and unusual and rare elements. This residual magma
eventually formed dikes that solidified into nepheline syenite
pegmatites containing pockets of well-developed mineral crystals. Today,
these pegmatite dikes outcrop on the faces of sheer, 2,000-foot-high
cliffs. After these cliffs yielded their first specimens in the late
1980s, they were quickly recognized as a classic locality for aegirine.
The write-up has a special section on the Great Rift Valley, considered
by some geologists to be Earth's most interesting geological area. The
aegirine forms primarily as long thin blades, similar to stibnite, but
shiny black rather than metallic gray. Gold-level members will receive a
single long thin blade about 2.5 to 3.5" in length. We do have some
specimens consisting of aegirine with cream-colored crystals of blocky
microcline, which we will be making available to Platinum members. |
Aegirine, Mount Malosa, Zomba
district, Malawi |
Aquamarine with black tourmaline, Erongo Mountain, Usakos and
Omaruru districts, Erongo Region, Namibia |
JULY 2011
AQUAMARINE Our aquamarine specimens were collected at Erongo
Mountain in the Usakos and Omaruru districts, Erongo Region, Namibia.
Erongo Mountain, a prominent, semicircular mountain 18 miles in
diameter, is located in west-central Namibia about 125 miles northwest
of the national capital of Windhoek. The origin of our specimens goes
back 135 million years ago to the late Jurassic Period when a volcanic
system subsided and collapsed to form a caldera. This fractured caldera
was then intruded by magma that emplaced the alkaline (silica-poor)
Erongo granite formation. This intrusion solidified very slowly, leaving
pockets of residual magma that were enriched with such unusual elements
as tin, tungsten, boron, fluorine, and beryllium. In areas where gases
created cavities, final solidification of the residual magma took place
on a mineral-by-mineral basis with the growth of large, well-developed
crystals. The write-up you will receive with your aquamarine crystal
will have lots more information, including a special section on the
unique element berylium. The aquamarine crystals are smaller than what we typically send Gold- and
Platinum-level members. |
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AUGUST 2011
DOLOMITE Our dolomite specimens are from the Shangbao Pyrite Mine in Leiyang
County, Hengyang Prefecture, Hunan Province, People’s Republic of China.
The Shangbao Pyrite Mine is located 15 miles southeast of the city of
Leiyang in a historic iron-mining region. In 1972, several small,
iron-sulfur mines were consolidated into the Shangbao Pyrite Mine, which
used a combination of open-pit and underground mining methods to extract
pyrite ore as a source of both iron and sulfur. Shangbao exploits a
skarn-type pyrite deposit that formed through the contact metamorphism
of limestone and dolomitic limestone. Mineral specimens from the
Shangbao Pyrite Mine first reached international markets in the 1980s.
When Shangbao ceased commercial operations in 1995, it was one of the
world’s few remaining mines that still exploited pyrite as a source of
iron. Immediately after the mine closed, a group of former pyrite miners
formed a syndicate and leased parts of the mine specifically to collect
specimens. Our specimens were recovered from a skarn pocket that was
opened in 2008. The write-up you will receive with your dolomite
specimen will have lots more information, including a special section on
the unique element magnesium. |
Dolomite, Shangbao Pyrite Mine, Leiyang County, Hengyang Prefecture,
Hunan Province, China |
ANHYDRITE, Naica Mine at Naica, Municipo de Saucillo, Chihuahua,
Mexico |
SEPTEMBER 2011
ANHYDRITE Our specimens are from the Naica Mine at Naica, Municipo
de Saucillo, Chihuahua, Mexico, an area that is 230 miles south of El
Paso, Texas. Spanish prospectors discovered the Naica multi-metal
deposit in 1794 and mined it for silver. The Naica Mine has operated
more-or-less steadily for more than 200 years and produces lead, zinc,
and smaller amounts of silver, copper, and gold. Its historic production
exceeds 40 million tons of ore. Naica is Mexico’s oldest producing mine,
its leading source of lead, and southern Chihuahua’s biggest private
employer. Naica first became recognized in the 1970s as a source of
mineral specimens, initially for crystals of fluorite and pyrite. In
1981, miners blasted into a fault that was lined with thousands of flat,
square-terminated, pale, blue-gray anhydrite crystals that established
Naica as a classic locality for anhydrite. In 2000, Naica miners
discovered a natural geodic (geode-like) cave now known as La Cueva de
los Cristales Gigantes (the Cave of the Giant Crystals). Our write-up
includes a special section on this amazing discovery! |
OCTOBER 2011
BARITE Our barite specimens were collected at Cerro Huarihuyn (also
spelled Warihuayin) in the Miraflores District, Huamalíes Province,
Huánuco Department, Peru. Located in central Peru, the remote Miraflores
District covers 1,214 square miles and has 3,700 residents and an
average elevation of 8,000 feet. It is 200 air miles north-northeast of
the national capital of Lima and 125 air miles east of the Pacific
coast. Miraflores is not a major mining district, but is rather one of
many lesser-mineralized areas of the greater Andes region. Spanish
prospectors first visited what is now the Miraflores District in the
late 1500s, discovering mineralized outcrops that were of insufficient
size and richness to warrant mining. Our barite specimens were collected
at Cerro Huarihuyn (Huarihuyn Mountain), an 8,835-foot-high mountain
that is really a “hill” by Andean standards. Barite specimens from Cerro
Huarihuyn first reached international markets in the late 1990s, but
attracted little interest. Then in spring 2005, barite specimens
(including ours) with water-clear transparency and superb crystal
development were collected in quantity.
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Barite, Cerro Huarihuyn, Miraflores,
Huamalíes Province, Huánuco Department,
Peru. Two photos representing typical Gold-level specimens that Club
members will receive.
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Atacamite, Mt. Gunson, Stuart Shelf area of the Andamooka
Ranges-Lake Torrens region of South Australia, Australia. |
NOVEMBER 2011
ATACAMITE Copper ore was discovered at Mt. Gunson in 1875;
production began in 1899 from an open pit called the Main Open Cut.
Production increased sharply during World War II to help satisfy the
critical Allied demand for copper. Mt. Gunson shut down after the war as
ore grades and metal prices declined. The mine reopened in 1970 on a
larger scale with a new flotation-separation concentrator to treat
lower-grade ores. In 1974, the Cattlegrid Deposit, the source of our
specimens, opened adjacent to the Main Open Cut. By the time the
Cattlegrid Pit shut down in 1986, it had produced 7.2 million metric
tons of ore grading 1.9 percent copper that yielded 127,000 metric tons
of copper and 62 metric tons (more than 1.9 million troy ounces) of
silver. The Mt. Gunson copper deposit lies within a rift valley and is
part of South Australia’s Stuart Shelf-Adelaide Geosyncline Copper
Province. These copper deposits formed early in the Proterozoic Eon some
1.5 billion years ago when copper-rich hydrothermal solutions surged
upward from basement rock into an overlying formation of layered
sediments that is now known as the Stuart Shelf. Atacamite formed when
shallow deposits of copper-sulfide minerals oxidized in the presence of
chlorine ions from saline lake-bed evaporite minerals. Current
geological exploration has revealed a massive ore body grading almost
three percent copper along with lesser amounts of silver, lead, zinc,
and bismuth. Full-scale mining at Mt. Gunson will resume in 2014.
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DECEMBER 2011
CARNELIAN Our specimens were mined by a company that has extensive
gemstone mine and quarry holdings in Madagascar and also explores for
new deposits. It has operated in Madagascar since the early 1980s, is a
major employer of Madagascans, and operates two schools in remote mining
areas to benefit local children. The Amberjeby quarry is in a formation
of heavily weathered, volcanic rock. When this rock was emplaced, it
contained numerous barren vesicles that later filled with groundwater
solutions rich in silica and hematite. These solutions eventually formed
silica gels that solidified into the reddish carnelian variety of
microcrystalline quartz. As erosion and weathering reduced the basalt
formations into a coarse earth and gravel, the harder, more resistant
carnelian survived as nodules dispersed through the sediments. Mining is
conducted mainly by shallow digging, with blasting employed only when
necessary. |
Carnelian, Amberjeby, near the seaport city of Mahajanga in the
Boeny Region of northeast Madagascar. |
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Would you like to to receive all the minerals we've featured
in 2011? Order a 1 Year Silver-Level membership including January 2011-December
2011 for $72 (12 months
for the price of 9)
Would you like receive all twelve minerals we have featured
in 2011? Choose a 1 Year Gold-Level membership including January 2011 to
December 2011 for $275 (12 months
for the price of 10)
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Would you like receive all twelve minerals we have featured
in 2011? Choose a 1 Year Platinum-Level membership including January 2011 to
December 2011 for $600 (12 months
for the price of 10)
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