User:Pamela.im/sandbox

Article Evaluation - Corundum

I evaluated the Corundum page. In general, this page contains good information regarding Corundum. However, all the sections in the article are not well developed. There is missing information, and some topics are not clearly defined, making it confusing for a reader that is not familiar with geology or mineralogy. For example, in the "Geology and Occurrence" section, it gives a brief overview of locations where corundum can be found. However, it is missing information on how corundum actually forms, what conditions are necessary for its formation, the different types of deposits that it can be found in, and so on. Another problematic area is the "Structure and Physical Properties" section. It is so brief, and it is seems to be missing information on the crystallographic structure of the mineral.

The main areas that the article is lacking in is an explanation about corundum mining, uses of corundum, where it can be found (in what environments, rock types, etc.), and how it forms. I also strongly suggest adding a section or a brief explanation of the relation between corundum and its 2 gem varieties, ruby and sapphire. A lot of people don't know that ruby and sapphire are a gem variety of corundum; they have the same crystal structure with the only difference being the transition elements replacing Al in the structure to give ruby and sapphire their diagnostic colours. In the talk pages of the article, Wikipedians are even trying to figure out the relation between corundum and its gem constituents, and there seems to be quite a bit of confusion. All the sections in the article also need to be expanded to provide a more in-depth explanation of concepts.

In terms of the information present, I would say everything in the article is relevant to the topic and it provides a neutral standpoint. The references used are okay, but there needs to be more inclusion of scientific papers. This can provide the appropriate background to expand on all the ideas that are missing in the article.

There seems to be no rating in this article. I would give rate it a 5/10 just because it does include some relevant information to the topic.

It is currently part of 5 Wikiprojects: metalworking, geology, rocks & minerals, gemology & jewelry/gemstones, India/ Tamil Nadu.

Rare Earth Elements - Edits

Comments from Sarah You're off to a fantastic start. My only comment is that I'm not sure I'd put the use of REEs for interpreting geological processes under origin.

Calder Patterson and I will be editing the Rare-earth element page.

For the most part, the earlier segments (Introduction to Discovery and early history) are well-written and complete. Regardless, we will review these sections and make sure citations are complete and up to date.

As for the remaining sections, here are our proposed edits:

• The Origins section is missing a lot of information. There doesn't seem to be a proper explanation of the actual origin of REE. The supernova nucleosynthesis of REEs is mentioned, but it would be of interest to the article to explain the relation of this origin to the Oddo-Harkins rule. This rule explains how atoms form through a supernova nucleosynthesis, and can be used to explain the formation of REE including their relative high and low element chondritic abundances. Following, we will add a section explaining the difference between light REE and heavy REE.
• In addition, we want to expand the Origins section to explain how REEs are used for geochemistry. There is no section as of now that mentions how REEs are used as indicators for geological processes. Here we will take into account the importance of REEs for sedimentary, igneous, and metamorphic rocks. We will also include a brief explanation of the importance of REEs in water.
• We believe the Geological Distribution section should be entirely re-written to be in phase with current geologic understanding and terminology - the original writing was done by a physicist in reference to a chemistry textbook, not in a geological context. The chemistry side of the discussion should be included, but should not be the sole focus of this section.
• Depending on how restructuring goes, we might merge the Origin and Geological Distribution sections, as these appear to correlate. For example, we need to add the initial partitioning of elements in protoearth, including an explanation or reference to partition coefficients and incompatibility, and how REEs concentrate by partial melting causing differentiation in different systems. This in turn, reflects the current geologic distribution that we observe in REEs today.
• This section will then culminate into the different REE deposit types. We will give a very brief summary of these, but will primarily link to the primary deposit pages instead. In addition, we will do a review of these pages to make sure they are up to date.
• For the Global rare-earth production section we want to change the focus from China to a more global perspective instead as there appears to be a Chinese bias. We want to add the top 5 producers (maybe include some charts reflecting this). We also want to add an explanation as to why REE are being produced, and the main uses of REE in industry today. We will expand their uses in the production section, but will briefly mention them prior in the introduction. As a result, in the Introduction we will add a sub-heading for the uses of REEs in industry and in earth sciences.
• The production section hasn't been updated since 2010, so we will ensure statistics are up-to-date.

The main goal for us will be to give an earth science perspective to this article, which it is currently lacking.

References to be used (this list is still a work in progress). Reference 3 is available in the library. It is cited in the Rare-earth mineral page, and will be valuable to provide our edits with an interdisciplinary perspective:

Rare-Earth Element - Draft

Geological Distribution - to be added supplementary to the existing section

During the sequential accretion of the Earth, the dense rare-earth elements were incorporated into the inner portions of the Earth. During early differentiation, the rare-earths were largely incorporated into Mantle rocks, leaving the crust depleted in rare-earths. Due to the high field strength and large ionic radius of rare-earths, they are incompatible with the crystal lattices of most rock-forming minerals, so REE will partition into a melt phase if one is present. Light rare-earth elements have larger ionic radii than heavy rare-earth elements, this is called lanthanide contraction, as a result, LREE are more incompatible and will partition more strongly into a melt phase than HREE, which may prefer to remain in the crystalline residue, particularly if it contains abundant Garnet. In allmagmas formed from partial melting, HREE will be more depleted than LREE. Enriched deposits of rare-earth elements at the surface of the Earth are often related to alkaline plutonism, an uncommon kind of differentiated magmatism that occurs in tectonic settings where there is rifting or that are near subduction zones. In a rift setting, the alkaline magma is produced by very small degrees of partial melting (<1%) of garnet peridotite in the upper mantle (200 to 600 km depth). This melt becomes enriched in incompatible elements, like the rare-earth elements, by leaching them out of the crystalline residue. The resultant magma rises as a diapir, or diatreme, along pre-existing fractures, and can be emplaced deep in the crust, or erupted at the surface. Typical REE enriched deposits types forming from these melts are carbonatites, and A- and M-Type granitoids. Near subduction zones, partial melting of the subducting plate within the asthenosphere (80 to 200 km depth) produces a volatile-rich magma (containing high concentrations of CO₂ and water) and with high concentrations of alkaline elements, and high element mobility that the rare-earths are strongly partitioned into. This melt will also rise along pre-existing fractures and is emplaced in the crust above the subducting slab or erupted at the surface. REE enriched deposits forming from these melts are typically S-Type granitoids.

Alkaline magmas enriched with rare-earth elements include carbonatites, peralkaline granites (pegmatites), and nepheline syenite. Carbonatites crystallize from CO₂-rich fluids, which can be produced by partial melting of hydrous-carbonated lherzolite to produce a CO₂-rich primary magma, by fractional crystallization of an alkaline primary magma, or by separation of a CO₂-rich immiscible liquid from. These liquids are most commonly forming in association with very deep Precambrian Cratons, like the ones found in Africa and the Canadian Shield. Ferrocarbonatites are the most common type of carbonatite to be enriched in REE, and are often emplaced as late-stage, brecciated pipes at the core of igneous complexes; they consist of fine-grained calcite and hematite, sometimes with significant concentrations of ankerite and minor concentrations of siderite. Large carbonatite deposits enriched in rare-earth elements include Mount Weld in Australia, Thor Lake in Canada, Zandkopsdrift in South Africa, and Mountain Pass in the USA. Peralkaline granites (A-Type granitoids) have very high concentrations of alkaline elements and very low concentrations of phosphorous; they are deposited at moderate depths in extensional zones, often as igneous ring complexes, or as pipes, massive bodies, and lenses. These fluids have very low viscosities and high element mobility, which allows for crystallization of large grains, despite a relatively short crystallization time upon emplacement; their large grain size is why these deposits are commonly referred to as pegmatites. Economically viable pegmatites are divided into Lithium-Cesium-Tantalum (LCT) and Niobium-Yttrium-Fluorine (NYF) types. NYF types are enriched in rare-earth minerals. Examples of rare-earth pegmatite deposits include Strange Lake in Canada, and Khaladean-Buregtey in Mongolia. Nepheline syenite (M-Type granitoids) deposits are comprised of 90% feldspar and feldspathoid minerals, and are deposited in small, circular massifs. They contain high concentrations of rare-earth-bearing accessory minerals. For the most part these deposits are small but important examples include Illimaussaq-Kvanefeld in Greenland, and Lovozera in Russia.

Rare-earth elements can also be enriched in deposits by secondary alteration either by interactions with hydrothermal fluids or meteoric water. Argillization of primary minerals enriches insoluble elements by leaching out silica and other soluble elements, recrystallizing feldspar into clay minerals such kaolinite, halloysite and montmorillonite. In tropical regions where precipitation is high, weathering forms a thick argillized regolith, this process is called supergene enrichment and produces laterite deposits; heavy rare-earth elements are incorporated into the residual clay by absorption. This kind of deposit is only mined in Southern China, where the majority of global heavy rare-earth element production occurs. Laterites do form elsewhere, including over the carbonatite at Mount Weld in Australia.

---> Stats for the mentioned deposits to come. -Calder

Geochemistry Applications - this will be a new section

The application of rare-earth elements to geology is important to understanding the petrological mechanisms of igneous, sedimentary and metamorphic rock formation. In geochemistry, rare-earth elements can be used to infer the petrological mechanisms that have affected a rock. The importance of rare-earth elements in petrological processes is due to the subtle atomic size differences between the rare-earth elements, which causes preferential fractionation of some elements relative to others depending on the processes at work.

In geochemistry, rare-earth elements are typically presented in normalized "spider" diagrams, in which concentration of rare-earth elements are normalized to a reference standard and are then expressed as the logarithm to the base 10 of the value. Commonly, the rare-earth elements are normalized to chondritic meteorites, as these are believed to be the closest representation of unfractionated solar system material. However, other normalizing standards can be applied depending on the purpose of the study. Normalization to a standard reference value, especially of a material believed to be unfractionated, allows the observed abundances to be compared to initial abundances of the element. Normalization also removes the pronounced ‘zig-zag’ pattern caused by the differences in abundance between even and odd atomic numbers. The trends that are observed in "spider" diagrams are typically referred to as "patterns" which may be diagnostic, or may be used to identify, petrological processes that have affected the material of interest.

The rare-earth elements patterns observed in igneous rocks are primarily a function of the chemistry of the source where the rock came from, as well as fractionation history the rock has undergone. Fractionation, is in turn a function of the partition coefficients of each element. Partition coefficients are responsible for the fractionation of a trace elements (including rare-earth elements) into the liquid phase (the melt/magma) or into the solid phase (the mineral). If an element preferentially remains in the solid phase it is termed ‘compatible’, and it preferentially partitions into the melt phase it is described as ‘incompatible’. Each element has a different partition coefficient, and therefore fractionates into solid and liquid phases distinctly. These concepts are also applicable to metamorphic and sedimentary petrology.

In igneous rocks, particularly in felsic melts, the following observations apply:  anomalies in Eu are dominated by the crystallization of feldspars. Hornblende, controls the enrichment of middle rare-earth elements (MREE) compared to light and heavy rare earth elements (LREE and HREE, respectively). Depletion of light relative to heavy rare-earth elements may be due to the crystallization of olivine, orthopyroxene, and clinopyroxene. On the other hand, depletion of heavy relative to light rare-earth elements may be due to the presence of garnet, as garnet preferentially incorporates heavy rare-earth elements into its crystal structure. The presence of zircon may also cause a similar effect.

In sedimentary rocks, rare-earth elements in clastic sediments are a representation provenance. The rare-earth element concentrations are not typically affected by sea and river waters, as rare-earth elements are insoluble and thus have very low concentrations in these fluids. As a result, when a sediment is transported, rare-earth element concentrations are unaffected by the fluid and instead the rock retains the rare-earth element concentration from its source.

As stated, sea and river waters typically have low rare-earth element concentrations. However, aqueous geochemistry is still very important. In oceans rare-earth elements reflect input from rivers, hydrothermal vents, and aeolian sources; this is important in the investigation of ocean mixing and circulation.

Rare-earth elements are also useful for dating rocks, as some radioactive isotopes display long half-lives. Of particular interest are the 138La-138Ce, 147Sm-143Nd, and 176Lu-176Hf systems.

Light versus Heavy Rare Earth Elements - this will supplementary to information on the site

The classification of light, heavy, and less commonly used middle rare earth elements is inconsistent between authors. However, the distinction is made by atomic numbers; those with low atomic numbers are referred to as light rare-earth elements, those with high atomic numbers are the heavy rare-earth elements, and those that fall in between are typically referred to as the middle rare-earth elements, and are typically between Sm to Ho. Typically, rare-earth elements with atomic numbers 57 to 61 are classified as light and those with atomic numbers higher greater than 62 (corresponding to Eu) are classified as heavy-rare earth elements. Eu is left out of this classification as it has two valance states: Eu+2 and Eu+3. It should be noted that Y is grouped as heavy rare-earth element due to chemical similarities. The differences in atomic numbers between light and heavy rare-earth elements causes differences in atomic radii throughout the different elements, causing chemical variations between the groups. As a result of atomic radii, light and heavy rare-earth elements fractionate differently into crystallizing minerals.

Uses of Rare earth elements - This will be a new section

The uses, applications, and demand of rare-earth elements has expanded over the years. This is particularly due to the uses of rare-earth elements in low-carbon technologies. Some important uses of rare-earth elements are applicable to the production of high-performance magnets, catalysts, alloys, glasses, and electronics. Nd is of interest to magnet production. Rare-earth elements in this category are used in the electric motors of hybrid vehicles, wind turbines, hard disc drives, portable electronics, microphones, speakers.  Ce and La are important as catalysts, and they are used for petroleum refining and as diesel additives. Additionally, Ce, La and Ne are important for alloy making, and are applicable to the production of fuel cells and Nickel-metal hybride batteries.  Ce, Ga and Nd are important for electronics; they are used in the production of LCD and plasma screens, fiber optics, lasers, as well as medical imaging. Additional uses of rare earth elements are as tracers in medical applications, fertilizes, and in water treatment.