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Posts tagged with "Mineralogy"

New Mineral(s)

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There are by now nearly 4000 known minerals. An astounding number of about 30 to 50 new minerals are described and one or two minerals are discredited each year, so the number is rapidly increasing. One of the recently discovered minerals is named in honour of Kazakh President Nursultan Nazarbayev. The new mineral was named Nurnazen -- an acronym of the name and surname of Nursultan Nazarbayev. It is a mineral from the hydrocarbon clusters and has promising scientific and practical uses for medical and chemical technology.

There is of course also a rare mineral named nielsenite (not in honour of me!).





Academics

Krokite, New Mineral Found in Meteorite

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A new mineral has been found in a carbonaceous chondrite meteorite from North-West Africa. The mineral is named Krokite after Alexander N. Krot, a Mānoa researcher known for his achievements in meteoritics. The discovery was announced In the May-June issue of the journal American Mineralogist.



In Danish:




Academics

Rare Earth Elements and Arfvedsonite, Greenland

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All the talk about rare earth elements these days gives me the opportunity to show you one of my mineral photos.



The image shows radiating crystals of arfvedsonite, a sodium rich amphibole. The connections with rare earth elements is that arfvedsonite is an agpaitic minreal, and that the photo is from the Ilímaussaq Intrusion in Greenland. Agpaites are unusually rich in rare and obscure minerals including minerals containing rare earth elements. The agpaitic rocks of the Ilímaussaq alkaline complex and their pegmatites are rich in the rare earth elements, their average rare earth elements content being up to thirty times higher than the average contents in the Earth’s crust. The Ilimaussaq intrusive complex is a large alkalic layered intrusion located on the southwest coast of Greenland. It is Mesoproterozoic in age (the Mesoproterozoic Era occurred between 1600 and 1000 million years ago). The Ilimaussaq Complex formed in a continental rift setting approximately 1160 million years ago. The complex is noted for a wide variety of rare minerals and is the type locality for thirty minerals, including: aenigmatite, arfvedsonite, sodalite, eudialyte and tugtupite - a paradise for mineral collectors.

The plans to mine rare earth elements at Kvanefjeld (or Kuannersuit as it is called in Greenlandish), near Narsaq, are well advanced as a multi-element project. There used to be uranium mines in the area,1958-1980. Until recently, however, the Greenland Ministry for Industry and Mineral Resources practised a zero tolerance policy for uranium mining. Greenland’s government has now amended the standard terms for exploration licences, which will allow development of the Kvanefjeld project for its rare earth elements, uranium and zinc. Greenland Minerals said it can now commit to definitive feasibility studies in 2011, as planned, after the decades-old ban on uranium mining was essentially lifted.

The Kvanefjeld deposit is located on the southwest tip of Greenland and is one of the largest undeveloped multi-element (rare earth elements, sodium fluoride and uranium) occurrences in the world. A pre-feasibility study estimates the mine can produce 43,729 metric tonnes of rare earths oxides and 3895 metric tonnes of uranium a year during a 23-year lifespan.

China now mines 95 % of the world’s rare earth elements, which have wide commercial and military applications and are vital to the manufacture of products like mobile phones, motors for electric vehicles, large wind turbines and guided missiles. To the alarm of its trading partners, China imposed increasingly tight export quotas on rare earths in the past two years, citing growing domestic demand and environmental concerns. In July 2010, Beijing reduced its export quota for rare earths for the second half of the year by 72 %.

The rest of the world is now of course looking for new/other rare earth elements resources, and on this background the Greenland deposit is important.





Academics

Microbial Dolomite in Abu Dhabi

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Half or more of the world's oil is produced from carbonate reservoir rocks (limestone or dolomite). Porosity is an important issue for reservoir rocks. Dolomites are normally less porous than limestones at shallow depths, but they retain their porosity better during burial and are less affected by compaction. What I am getting at is that the oil industry is deeply interested in dolomite research. It is therefore no surprise that a paper like “Microbial Dolomites from Carbonate-Evaporite Sediments of the Coastal Sabkha of Abu Dhabi and their Implications” is published in a journal like the “Journal of Petroleum Geology”

Formation of dolomite may sound simple. You take some limestone, which consists of calcite (CaCO3) and add some Magnesium (Mg) to get dolomite CaMg(CO3)2), a process used to be called dolomitization. A problem is that this doesn't seem to work in the lab. The assumed chemical reaction will not take place at low temperature and atmospheric pressure. Calcium carbonate does not react with magnesium cations in solution at room temperature: no conversion of limestone into dolomite is therefore possible under conditions typical of the earth's surface. (Instead you may possibly end up with a magnesium rich limestone - “magnesium limestone”). No reaction can be measured to take place at room temperature between calcium carbonate and magnesium sulphate or magnesium chloride in solution. A working trick is to add the right bacteria to your mixture.

If the water is slightly alkaline, dolomite formation might take place via a reaction a bit like this:

Mg2+ + HCO3 + CaCO3 <--> CaMg(CO3)2 + H+
with the necessary bicarbonate (HCO3) supplied by bacterial sulphate reduction.

Past studies have shown that microbially-mediated dolomite formation may be associated with activity of sulphate reducing bacteria. This bacterial sulphate reduction, combined with oxidation of organic matter, results in increasing alkalinity, promoting dolomite precipitation. Sadooni and co-authors show that dolomite in recent sabkha sediments from Abu Dhabi appears to be initiated in what they call “micro-niches” or small isolated nucleation sites. The dolomite occurred in nucleation sites such as pores in foraminiferal tests (popularly known as shells) and micro-depressions between clay mineral plates. Local anoxia (oxygen depletion) at these sites may permit microbial sulphate reduction and dolomite formation. Combination of neighbouring micro-niches in porous carbonate sediments would lead to dolomitization of an entire section.

The study suggests that “microbial” dolomite may be more widespread than has been previously recognised.

I wonder whether dolomite formation is at all possible without some sort of microbial mediation, but have no answer ready for that.

I understand that the exact role of microbes in dolomite formation is not fully understood, but it is suggested that during bacterial sulphate reduction, organic matter is oxidised, and the alkalinity increases promoting dolomite formation. As sulphate is consumed MgSO4 (magnesium sulphate) becomes disassociated and Mg++ comes available for further dolomite formation.


Reference:
Sadoon et al.
Microbial Dolomites from Carbonate-Evaporite Sediments of the Coastal Sabkha of Abu Dhabi and their Implications
Journal of Petroleum Geology, Vol. 33(4), October 2010, pp 289-298





Academics

Malachite, Congo, and the Copperbelt

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Later this year (on 30 June 2010) the Democratic Republic of the Congo will celebrate its 50 years of independence. The DR Congo, previously known as Zaire, is immensely rich in natural resources and is thought to be, by all accounts, the wealthiest country on earth in regards to natural resources. The country is potentially rich but partially ruined. It is a long story of power, money and natural resources - i.e. abused power, money into the “wrong pockets”, and income from mining of natural resources spent on warfare.

Reasons enough to show you one of my treasures from Katanga, Congo - a hand specimen of malachite.



Malachite is a copper carbonate found in oxidised zones of copper deposits. Limestone, or dolomite, around the copper deposits will be the source of the carbonate. A large belt of copper deposits - actually called the “copperbelt” - is stretching from Katanga into Zambia. The Copperbelt is one of the richest sources of copper in the world. Cobalt, selenium, silver, and gold are also produced in this belt. The Central African Copperbelt is one of the world's greatest metallogenic provinces containing 34% of the world's cobalt reserves and over 10% of the world's copper reserves.

Most metal ore deposits can in one way or another be related to plate tectonics. In terms of global resources of copper the most important are porphyry copper deposits found in relation to subduction zones. Second in importance are rift related deposits or rift related stratiform deposits, such as the Copperbelt copper deposits. Such deposits tend to contain ore grades that are distinctly higher than typical porphyry copper deposits (as those in the Andes). The copperbelt deposits occurred within the first marine transgressive unit (of shale and sandstone) laid down after a period of redbed sedimentation.



On 11 July 1960 Katanga separated itself from the newly independent Democratic Republic of the Congo. The state was however reunited with DR Congo in 1963. In 1971 Katanga was renamed Shaba, (very appropriately) from the Swahili word for 'brass' (a borrowing from Arabic shabah). Throughout the 1970s a number of insurrections were put down, and he province became Katanga again in 1997.

Congo Provinces:
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Academics



North and South Islands - New Names?

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A move is underway to give New Zealand's two main islands official Maori names as well as to formalise the currently used names North and South.

The New Zealand Geographic Board says it's time to sort out the names for each island after it was discovered no formal names were ever given to the two chunks of land despite more than 200 years of common usage of those names.

The Maori names Te Ika a Maui for the North Island and Te Wai Pounamu for the South Island appeared on early official maps and documents, but from the 1950s that Maori names of the two main islands stopped appearing on official maps.

Maori know North Island as Te Ika a Maui or "the fish of Maui", based on a legend about how the god Maui hauled the island up from the sea while fishing.

The Maori name of South Island was Te Wai Pounamu, which means "place of greenstone" after the island's outcrops of jade, from which tribes traditionally crafted weapons and jewellery.

New Zealand greenstone (or New Zealand jade) is either the mineral nephrite (Maori: pounamu) or bowenite (Maori: tangiwai.) Nephrite is obtained from the Taramakau-Arahura region as river boulders washed down from the parent rock in the Southern Alps; bowenite is found as beach boulders and pebbles at Anita Bay in Milford Sound. Some nephrite is also obtained from the Wakatipu region.

In gemstone quality nephrite is generally known as jade. The name nephrite is derived from lapis nephriticus, which means 'kidney stone' and is the Latin version of the Spanish ‘piedra de ijada’ (the English word 'jade' is indeed derived from the Spanish term ‘piedra de ijada’). Accordingly, nephrite jade was once believed to be a cure for kidney stones.

http://www.telegraph.co.uk/news/worldnews/australiaandthepacific/newzealand/5194535/New-Zealands-North-and-South-Islands-could-be-renamed.html
http://tvnz.co.nz/national-news/maori-names-north-and-south-islands-2662407
http://www.teara.govt.nz/1966/G/Greenstone/Greenstone/en



Core-Mantle Boundary

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Can slabs of oceanic crust descend as deep as to the core-mantle boundary? Is cold mid-ocean-ridge basalt dense enough to sink so deep into the mantle?

Do mantle plumes exist? And if so, can they well up from as deep as the core-mantle boundary?

These and other core-mantle boundary related questions are occupying many earth scientists. They just want to know.

Most of our earlier knowledge of the Earth's interior came from studying seismic waves (after earthquakes). It became clear that the boundary between the core and the mantle was something special. S-waves (secondary wave or shear wave) stopped. They cannot propagate through liquids. Seismic velocity is linked to the density of the medium through which the waves travel. P-wave (primary wave) velocity in general increases with increasing density - In liquids, however, the speed will be less. The core is much denser than the mantle.

When it was discovered that a thin layer directly above the core-mantle boundary had some mysterious properties it had to get a name consistent with the naming of the earth’s layers in the middle of last century. It is now still referred to as the D" ("D double-prime" or "D prime prime"). The D" name originates from the mathematician Keith Bullen's designations for the Earth's layers. His system was to label each layer alphabetically, A through G, with the crust as 'A' and the inner core as 'G'. In his 1942 publication of his model, the entire lower mantle was the D layer. In 1950, Bullen found his "D" layer to actually be two different layers. The upper part of the D layer, about 1800 km thick, was renamed D’ (D prime) and the lower part (the bottom 200 km) was named D" (pronounced "dee double prime"). A layer that produces strange seismic properties.

Research into the mysteries of the D“ layer has advanced spectacularly since 2004, when Japanese researchers found that high temperatures and pressures like those existing in the D” layer transform perovskite, the major mineral in Earth's mantle. The publication in the journal Science of Post-Perovskite Phase Transition in MgSiO3 is seen as a turning point. Since then many papers on this topic have followed. The latest I have seen is Radiative conductivity in the Earth's lower mantle by Goncharov et al. in today’s (13 November 2008) issue of Nature.

The discovery of post-perovskovite has profound implications for the chemical, thermal, and dynamical structure of the lowermost mantle (the D” region). Several major seismological characteristics of the D” region can now be explained by the presence of post-perovskite, and the specific properties of the phase transition provide the first direct constraints on absolute temperature and temperature gradients in the lowermost mantle. A discussion of the current understanding of the core–mantle boundary region can be found in Discovery of Post-Perovskite and New Views on the Core–Mantle Boundary Region by Kei Hirose and Thorne Lay in Elements of June 2008 (DOI: 10.2113/GSELEMENTS.4.3.183 - start downloading of the full article as large pdf-file by clicking here).

The Mg2+ site in post-perovskite is smaller than in perovskite, resulting in a volume reduction of 1.0–1.5%. Unlike perovskite, the post-perovskite phase has a layered structure of the SiO6 octahedra, which may lead to a large contrast in some properties with perovskite.


Scenario for the D” region. The D” seismic discontinuity is caused by the perovskite (Pv) to post-perovskite (PPv) phase transition. Post-perovskite may transform back to perovskite in the bottom thermal boundary layer with a steep temperature gradient. The large low-shear-velocity provinces (LLSVP) underneath upwellings (forming plumes) possibly represent large accumulations of dense MORB-enriched materials. The solid residue formed by partial melting in the ultralow-velocity zone (ULVZ - thin reddish zone on image) might also be involved in upwelling plumes. Such thin (20-40 km) ULVZ-layers are mainly (but not only) found under the Pacific Ocean and under Africa.

http://www.eurekalert.org/pub_releases/2008-11/ci-eht111008.php
http://www.cems.umn.edu/research/wentzcovitch/highlights/science_now_040324.htm
http://olivine.ethz.ch/~artem/NewMinerals.html
http://www.ucsc.edu/news_events/press_releases/text.asp?pid=978
http://www.nature.com/ngeo/journal/v1/n1/full/ngeo.2007.44.html (full paper in HTML)

For my (increasing number of) Scandinavian readers there is review in Norwegian at Geoportalen - http://www.geoportalen.no/planetenjorden/jordensindre/revolusjon/ . The article here by Reidar G. Trønnes, Natural History Museum, Universitty of Oslo, on the Earth’s Interior is somewhat easier to consume, and is well illustrated.

Maybe I ought to add that some of the topics discussed in the (review) papers are still controversial.




Nielsenite

In Greenland I have seen some minerals, that I had never even heard of before. Greenland is a really nice place - in summer! It is a bit difficult to get around as there are no roads connecting the (small) villages. Traffic is mainly by boat or helicopter. A place that I had hoped to visit this summer is the Skaergaard intrusion, but in the end I couldn’t go, because of other obligations. It may be my last chance. The Skaergaard intrusion is a 54.5 million years old world famous layered intrusion at the coast of East Greenland. The intrusion was emplaced during the build up of the regional flood basalts and the initial stages of continental rifting and seafloor spreading in the North Atlantic. The original magma volume was ca. 300 km3.

Here is a report from somebody else's field trip to the Skaergaard intrusion. And here is more information for those interested.

A mineral found at the Skaergaard intrusion is Nielsenite. Nielsenite is a very rare mineral. So far it has in fact only been found at the Skaergaard intrusion. It was found by the Russian Geologist Nikolai S. Rudashevsky in samples collected by a Danish geologist by the name of Nielsen, so Rudashevsky suggested to call it Nielsenite. The mineral is described in a recent publication by Rudashevsky et al. in The Canadian Mineralogist, the journal of the Mineralogical Association of Canada. This was the first detailed description of the mineral. The name Nielsenite was recognised in 2004. Do not expect ever to see Nielsenite with your naked eye. The examples found are so small that you need a scanning electron microscope (SEM) to see the mineral. Many new minerals have been discovered by use of SEM since the 1970-ties, and for the time being something like 50-70 new minerals are discovered per year. When I started being especially interested in minerals there were around 2000 different known minerals. Where will it end? Around 7000? that would be around the same number as of bird species in the whole world - another of my interests - or will it be around 11000? I just don’t know!

The Nielsen in question is of course not Ole Nielsen, but Troels F. D. Nielsen, from the Geological Survey of Denmark and Greenland (GEUS). Troels Nielsen has been very active in the research in the Skaergaard area.

Here are some facts about Nielsenite
Formula: PdCu3
Crystallography: Tetragonal
Hardness: Not determined
Density (computed): 9,527 g/cm3
Streak: Black
Cleavage: None
Colour: Steel grey
Fracture: Conchoidal (or shell-shaped)
Transparency (or diaphaniety): Opaque
Locality: Skaergaard intrusion, 68° N, East Greenland

Explanation of some of the terms:
PdCu3 - Pd is palladium and Cu is copper. Palladium is a rare and lustrous silvery-white metal. So Nielsenite is composed of palladium and copper.
Crystallography - There are seven crystal systems: Cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic and triclinic
Mohs’ scale of hardness goes from 1 (talc) to 10 (diamond).
Streak (also called powder color) is the powder mark left by a mineral as it is drawn across an unglazed piece of porcelain (a streak plate).
Fracture is a term used to describe the shape and texture of the surface formed when a mineral is broken. Fracture differs from cleavage.

Links
In English:
http://www.mindat.org/min-26983.html
http://www.mindat.org/locentry-272687.html
In Danish:
http://videnskab.dk/content/dk/naturvidenskab/mineral_opkaldt_efter_nielsen
http://www.geus.dk/geuspage-dk.htm?http://www.geus.dk/cgi-bin/webbasen_nyt.pl?id=1213005616&cgifunction=form





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