Rocks - Science topic

I assume that you are referring to the Burgers vector as being either [100], [010], or [001]. Because rock salt has cubic symmetry, <100> directions are equivalent in that structure.

Terrigenous rocks: Derived fom land or continents, mainly used to discriminate the source of sediment in (coastal) matrine environments

Detrital rocks: composed of fragments and particulate matter derived from pre-existing rocks by erosion, weathering and laid down after transport or left in situ. Classification is used when when present in rocks at a an amount of > 50 % detrial matter

Clastic rocks: composed of fragments of prexisting rocks.

The particles can be minerals or lithoclasts of different grain size from shale to conglomerate (pelite, arenite, rudite) or a regolith. Applicable to all three categories. Transport, compaction and diagenetic alteration are no modifier or reason for differentiation in this tripartite scheme

HGD

Ali Al.Qassab Thank you for your response! I have created the following pseudosection from a metapelite. I know from other research that the area of study has undergone two different metamorphic phases a prograde and a retrograde. Is it safe to assume that those two areas in the diagram represent the two different phases?

The mineral assemblage of the rock is:

Qtz+Pl(Ab)+Mica(Ms)+Bt+Gt(Alm)+St+Sil

I think it can be possible in ophiolite peridotites.

I think it can be possible diamond ore deposits in ophiolites.

Ever since I received my degree in geological engineering, it has been my main goal to understand the geology of any surface area. Experience so far shows that it is easy to understand.

Regards,

Laszlo

It should be the other way round. HREE is concentrated in Y-bearing regimes and hosted by xenotime. When the HREE are scavenged from the system the relative amount of LREE can also go up.

HGD

you can deploy Copilot Absolutely! Heavy Rare Earth Elements (HREE) deposits are typically associated with specific types of parent rocks. Here are some of the best-known parent rocks for HREE ore deposits:

### 1. **Alkaline Igneous Rocks**

- **Description**: These rocks are rich in alkali metals like sodium and potassium. They include nepheline syenites, trachytes, and peralkaline granites.

- **Examples**: The Kvanefjeld deposit in Greenland and the Strange Lake deposit in Canada are notable examples.

- **Minerals**: Common HREE-bearing minerals in these rocks include eudialyte, loparite, and fergusonite.

### 2. **Carbonatites**

- **Description**: These are igneous rocks composed predominantly of carbonate minerals.

- **Examples**: The Mountain Pass deposit in the USA and the Bayan Obo deposit in China are famous for their REE content.

- **Minerals**: HREEs in carbonatites are often found in minerals like bastnäsite and monazite.

### 3. **Hydrothermal Deposits**

- **Description**: These deposits form from hot, mineral-rich fluids that precipitate minerals in fractures and pores of rocks.

- **Examples**: The Browns Range in Australia is a significant hydrothermal HREE deposit.

- **Minerals**: Xenotime is a common HREE-bearing mineral in these deposits–xenotime ...](https://pubs.geoscienceworld.org/gsa/geology/article/46/3/263/526711/Hydrothermal-formation-of-heavy-rare-earth-element).

### 4. **Ion-Adsorption Clays**

- **Description**: These are weathered granitic rocks where REEs are adsorbed onto clay minerals.

- **Examples**: Southern China is known for its ion-adsorption clay deposits.

- **Minerals**: REEs are typically adsorbed onto minerals like kaolinite and halloysite.

### References

1. **[Rare Earth Element Deposits of Alkaline Igneous Rocks](https://www.mdpi.com/2079-9276/6/3/34)**

2. **[Hydrothermal Formation of HREE Deposits](https://pubs.geoscienceworld.org/gsa/geology/article/46/3/263/526711/Hydrothermal-formation-of-heavy-rare-earth-element)**

3. **[Conventional Rare Earth Element Mineral Deposits](https://link.springer.com/chapter/10.1007/978-3-031-31867-2_2)**

4. **[A Classification Scheme for Ore Deposits](https://bu.edu.eg/portal/uploads/Science/Geology/1400/crs-5058/Files/Basem%20Ahmed%20Zoheir_Ore%20geology%20course_lecture%2001.pdf)**

5. **[Rare Earth and Critical Elements in Ore Deposits](https://pubs.geoscienceworld.org/segweb/books/edited-volume/1998/chapter/16271168/Characteristics-and-Genesis-of-Ion-Adsorption-Type)**

These parent rocks are crucial for the formation of HREE deposits, and understanding their geology can help in the exploration and extraction of these valuable elements.

Good luck

I think it can be possible uranium bearing rocks in Eastern part of Iran.

I think soliceous carbonate rocks have been formed in ocean floor must be answere of this question.

I think it can be possible if rifting had been active at the past geology times in that area.

Dear Doctor

Go To

[ABSTRACT: We report for the first time the geochemistry of rare earth elements (REE) in the weathered crusts of I-type and calc-alkaline to high-K (shoshonitic) granitic rocks at Mamasa and Palu region, Sulawesi Island, Indonesia. The weathered crusts can be divided into horizon A (lateritic profile) and B (weathered horizon). Quartz, albite, kaolinite, halloysite and montmorrilonite prevail in the weathered crust. Both weathered profiles show that the total REE increased from the parent rocks to the horizon B but significantly decrease toward the upper part (horizon A). LREE are enriched toward the upper part of the profile as shown by La/YbN value. However, HREE concentrations are high in horizon B1 in Palu profile. The total REE content of the weathered crust are relatively elevated compared to the parent rocks, particularly in the lower part of horizon B in Mamasa profile and in horizon B2 in Palu profile. This suggests that REE-bearing accessory minerals may be resistant against weathering and may remain as residual phase in the weathered crusts. The normalized isocon diagram shows that the mass balance of major and REE components between each horizon in Mamasa and Palu weathering profile are different. The positive Ce anomaly in the horizon A of Mamasa profile indicated that Ce is rapidly precipitated during weathering and retain at the upper soil horizon.]

Dear Doctor

Go To

[Abstract

This article presents a description of Rare-earth elements (REE) which are a collection of seventeen metals that have distinctive and varied chemical, magnetic, and luminescent properties that make them strategically important in a number of high-technology industries. Consequently, the REE are increasingly becoming more attractive commodity targets for the mineral industry. This paper presents a comprehensive review of the distribution, geological characteristics and resources of Australia's major REE deposits. REE are generally associated with igneous, sedimentary, and metamorphic rocks in a wide range of geological environments. Elevated concentrations of these elements have been documented in various heavy-mineral sand deposits (beach, dune, marine tidal, and channel), carbonatite intrusions, (per)alkaline igneous rocks, iron-oxide breccia complexes, calc-silicate rocks (skarns), fluorapatite veins, pegmatites, phosphorites, fluviatile sandstones, unconformity-related uranium deposits, and lignites. The dissemination and deliberation of REE in these deposits are influenced by various rock-forming processes including enrichment in magmatic or hydrothermal fluids, separation into mineral species and precipitation, and subsequent redistribution and concentration through weathering and other surface processes. The lanthanide series of REE (lanthanum to lutetium) and yttrium show a close genetic and three-dimensional association with alkaline felsic igneous rocks, however, scandium in laterite profiles has a closer empathy with ultramafic/mafic igneous rocks. The highest level of the cataloguing comprises four general 'mineral-system association' categories, regolith, basinal, metamorphic, and magmatic, which in turn contain sixteen 'deposit type' members, namely: regolith-carbonatite-associated; ultramafic/mafic rock-associated; basinal-heavy mineral sand deposits in beach, high dune, offshore shallow marine tidal, and tidal environments; phosphorite; lignite; unconformity-related; metamorphic-calc-silicate; and magmatic-(per)alkaline rocks; carbonatite; pegmatite; skarn; apatite and/or fluorite veins; and iron-oxide breccia complex.]

This is a very broad question. HREE can be found in a wide array of rocks, and sediments. Monzanite (Ce,La,Y,The)PO4 is a phosphate member of the REE. It is highly radioactive and can contain up to 20% ThO2. Because this mineral is associated with SiO2 and other heavy elements - it is fairly resistant to weathering and is often found in sand deposits.

It can be derived from granites, aplites, pegmatites, and many different metamorphic rocks.

This is just one example of many.

The question should narrow down which mineral(s) you are after. Then the answers will be more precise.

Thanks for the comment John.

The classification of a rock should not be associated to its origin. Never. We should have the possibility to give a name to a rock independently on where it has been collected, what is its age, who collected it, the associated tectonic setting and, definitively, what is its petrogenetic origin. A rock should be classified based on petrography and, if available and if necessary and if useful, on its geochemistry. That's all. This is the first principle of the IUGS classification of rocks.

What you write is correct, but it is not directly linked to the choice to classify a mantle rock ultimately to an igneous origin. I agree with you that most of the peridotites and pyroxenites have a mantle origin (i.e., they crystallized from a magma ocean), but you should agree with me that their petrography is almost always typical of metamorphic rocks. All the classical articles dealing with the petrography of igneous rocks use terms exclusive of metamorphic rocks (granoblastic, pyrometamorphyc, mosaic, heteroblastic, and so on).

The problem is indeed here: we know that mantle rocks have a mantle origin, but their ultimate aspect in thin section is typical of metamorphic rocks. IUGS reccommends to use petrography as the first step to classify a rock as igneous or metamorphic. Following this rationale, most of the mantle rocks should be classified as metamorphic. Of course nobody would accept to delete peridotites and websterites from the igneous rock family, but I believe that it is important to write in the third edition of the IUGS book some comment stating that there is a great difficulty to classify this kind of rocks as igneous, considering their metamorphic textures. Harzburgites, dunites, lherzolites, wehrlites, olivin websterites, websterites and pyroxenites will remain in the igneous rock classification scheme, but some "caveat" has to be reported.

A last comment on your last phrase. I am sorry, but I disagreee with you. A metamorphic granite is no longer a granite, but it becomes as a metagranite (i.e., a metamorphic rocks with an igneous origin). It could be classified as gneiss or a migmatite, for example, but certainly a metamorphic granite is no longer a granite, otherwise we would have no metamorphic rocks at all.

Cheers,

michele

I think it can be uranium ore deposits.

I an sure kimberlites are correct answer to this question.

I think ca bearing rocks such as basalts and gabbros must be best candidate.

Hi Harald,

the problem is that real basalts do not have plagioclase/feldspars as low as 0.65, as instead reported in the QAPF diagram. Typical basalts (meaning >99% of the basalts) have plagioclase/feldspars >0.99 (practically = 1, i.e., have no alkali feldspars). We were simply proposing to think about this problem, reducing the width of the field of basalts. We were also wondering if anybody ever found foid-bearing andesites (which actually appear in the QAPF double triangle).

Cheers,

michele

I think Gold in ophiolites can be remaining of gold in syprus type massive sulfide that before serpentinization have formed in mid ocean ridge basalts in ophiolite.

I think it is not so correct for all of igneous rocks.

DEAR SHAHAB

GOOD MORNING AND THANK YOU FOR YOUR DETAILED REPLY. PLEASE READ CAREFULLY THE WHOLE ARTICLE ATTACHED TO THIS QUESTION, IT WILL GIVE ANSWERS TO ALL OF THE POINTS THAT YOU RAISED. REGARDING RECENT DIAMOND FINDINGS IN GREECE, MPOSKOS & KOSTOPOULOS 2001 HAVE FOUND UHP MICRODIAMONDS IN THE GREEK RHODOPE MASSIF (SEE PHOTO ATTACHED). THE ARTICLE IS ONE OF THE MOST CITED DIAMOND-RELATED PETROLOGICAL ARTICLES (WITH 337 CITATIONS).

BEST REGARDS

IOANNIS

Magnesite forms as an economic mineral in ultramafic rocks through the process of carbonation, where magnesium-rich minerals (e.g., olivine or serpentine) react with carbon dioxide-bearing fluids. This typically occurs under low to moderate temperatures (50–200°C) and high CO₂ concentrations in a hydrous environment. Magnesite deposition is often associated with hydrothermal systems, where fluids percolate through ultramafic rocks, promoting the transformation of magnesium silicates into carbonates. Tectonic settings like mid-ocean ridges, subduction zones, or ophiolite complexes provide the necessary fluid-rock interactions for its formation. Economic deposits are often linked to large-scale fault systems that enhance fluid circulation and carbonation reactions.

I THINK OPTION NUMBER 1 SOUNDS BETTER. IT IS DIFFICULT BUT NOT IMPOSSIBLE. LIKE MANY PETROLOGICAL TERMS, THE TERM PICROBASALT IS USED DIFFERENTLY BY EVERY GEOLOGIST. HOWEVER, YOU CAN ALWAYS FIND SOME OVERLAP IN THE DEFINITION.

BEST REGARDS

IOANNIS

Dear Gholamreza Fotoohi Rad ,

It's not worth getting too involved because it will confuse the healthy idea.

The classical earth theory is perfectly applicable to the Geology of Iran Therefore, I think the petrological description is clearer than the current one.

Regards,

Laszlo

I think acidic tuffs can be best candidate for good bentonites.

The big difference is the bulk rock composition (chemistry) of metapelites and mafic rocks that control the mineral parageneses. Cheers, Paola

I think if past tectonic has changed many times it is possible.

Regarding your first question, it is generally safe to crush and mill rock samples for geochemical analysis. The degree of safety depends on the specific machine, plate specifications, and the hardness of the rock being processed. To elaborate further, steel is a relatively hard material and can effectively pulverize most geological materials without undergoing significant corrosion, minimising the risk of contamination.

Regarding your second question, it is important to note that this is the standard procedure for pulverizing samples for geochemical analysis. While steel contains iron, contamination from other elements is typically minimal and often negligible for trace and rare earth element analysis. Even in extreme cases where the grinding plate undergoes slight corrosion, the additional iron content would be relatively small. It's important to remember that most geochemical analysis machines, such as XRF, quadrupole ICP, etc., have inherent measurement errors. Therefore, it's essential to strive for good analysis rather than aiming for perfection. If you have a pulveriser from a reputable brand that is suitable for grinding materials of the desired hardness, I recommend using it for your analysis.

I think it is possible yes.

I think because of magma composition is very suitable for accumulation of Cu in these magmas.

I think it can be possible.

In the name of Allah.

Hello dear Dr Fotohi.

Rocks that originate from the melting of the continental crust, such as alkaline granites, are usually more enriched in rare earth elements than other igneous rocks. Of course, these types of rocks usually show enrichment in light rare earth elements such as cerium, lanthaium and neodymium. Apatites of hydrothermal origin, such as apatites of Kiruna-type iron deposits, show enrichment of light rare earth elements. Marine sedimentary apatites (phosphorites) show enrichment of heavy rare earth elements. In general, rare earth elements geochemically have a close relationship with uranium and thorium.

I think it can be.

One type of gives host to U (hot granite) being well differentiated the others not. The process is too complex so as to be anwered with a simple answer only because in many cases it is not the granite, proper, but igneous rocks associated with the granite such as pegmatite, lamprophyres and veins of different composition that have gentically no link to the hosting granite except undergoing faulting and jointing.

HGD

See my comments on your question concerning Ne syenites

HGD

Ne syenites are deposits in their own rights and mined already as a non-metallic deposit. They are targeted upon for REE deposits and to a lesser extent Nb/Ta. They may be considered as unconventional concentrations of Be, U, Th, Al, Ga and Ti (currently not held to be economic)

HGD

Diamond (or micro-diamonds) in meta-ophiolites have been found in the NW Alps. The occurrence of diamonds depends on the tectono-metamorphic evolution that the rock has suffered. Not necessarily it can be found in ophiolite. Up to now, it has been found within garnet in metasediments.

I think it must be in alkali granites with high silica and high alkali feldspar.

Dear Michele Lustrino

I see that I arrived pretty late at the discussion, but I would like comment. I would agree with the point made by Harald G. Dill about classification schemes, but, in this case, where, despite purely descriptive origin, the name is now very closely associated with the process, I believe that adopting your proposal would end up creating more confusion, instead of creating more clarity. I would follow what you said in your answer to Dalibor Matýsek, i.e., classify "igneous" eclogites as ultramafic rocks with clinpyroxenite or garnetite compositions.

Cheers

Caio

Gholamreza Fotoohi Rad

Diatreme (volcanic vent): When hot material escapes from the Earth's interior in an eruption, the vent of the volcano and the feeder pipe below fill with breccia as the eruption wanes. The resulting structure is called a diatreme or volcanic vent. Much research has clarified the mechanism of diatreme formation. Studies of the minerals and rocks contained in some diatremes have shown that they only form at great depths - about 100 km or more - within the upper mantle. There is a diatreme in the legendary Kimberley Mines in South Africa, one of the largest diamond mines in the world. This diatreme is composed of peridotite, an ultramafic rock composed mostly of olivine and pyroxene. It also contains diamonds, which are formed from carbon under high pressure in the mantle with mixed fragments of mantle rock picked up by the magma as it rose to the Earth's surface. This diatreme is seen as if a well had been drilled into the mantle to a depth of 300 km. The fragments that the magma picked up as it rose provide the only direct evidence of the upper mantle material, which is composed mainly of peridotite.

I think it can be .

I think it can be about 60 percent.

I think it can be possible about 70 percent.

I think it is possible about 70 percent.

All physical-chemical characteristics, excluding rock color, e.g., hardness of the minerals and their texture and structure play a part. The ultimate stage when grinding is executed is paramorphism, simply explained when a minerals changes is X structure without any cheimical change. This might happen frequently with sulfides such as a change in the X lattice of pyrrhotite and wurtzite/sphalerite. Wurtzite which is a common ZnS in Andenian volcanc- and subvolcanic-related base metal deposits is metastable and grinding it for XRD powder diffraction in a mortar already triggers its conversion into sphalerite. I made this unexpected process during my Ph.D. studying wurtzite in Pb-Zn-Cu deposits in SW Tuscany, where wurtzite forms the so-called "blenda fibrosa" (German: Strahlenblende) DILL, H.G. (1979) Die Strahlenblende von Accesa (SW-Toskana, Italien). - Mineralogy and Petrology, 26: 271-278.

The only way out this dilema is a single-X-XRD investigation (Weißenberg Method). More than 90 % of the wurtzite was "paramorphosed" due to my handling it in a porcellain mortar. It leads to misleading interpretations of the physical regime. Please, check-out this phenomenon in those cases where different minerals or different X structure occur with the same chemical composition, especially in the class of sulfides and arsenides

HGD

dear Ioannis

The classification of lamprophyres, lamproites, and kimberlites has been a topic of ongoing discussion within the International Union of Geological Sciences (IUGS). Here are some key points from recent proposals and discussions:

These proposals aim to create a more accurate and comprehensive classification system that can be widely adopted by geologists.

Is there a specific aspect of this classification that interests you the most?

1: Integrating Ultramafic Lamprophyres into the IUGS Classification of Igneous Rocks 2: Classification of Lamprophyres, Lamproites, Kimberlites

This is one of the problem we are facing with.

michele

DEAR GHOLAMREZA

GOOD MORNING. IRAN IS SET AWAY FROM CRATONS AND PERI-CRATONIC MOBILE BELTS IN AN OROGENIC ENVIRONMENT. HOWEVER, UNCONVENTIONAL DIAMOND DEPOSITS IN SIMILAR ENVIRONMENTS HAVE BEEN FOUND IN BORNEO, THE URALS, NSW, CALIFORNIA, BURMA, THAILAND, VICTORIA, TASMANIA, IRELAND, N. ALGERIA AND SUMATRA. DO YOU KNOW FOR ANY MENTIONS OF DIAMONDS FROM IRAN? I KNOW OF AN ANCIENT GREEK DIAMOND RING FROM NEARBY AFGHANISTAN BUT THE DIAMOND SOURCE WAS PROBABLY INDIA.

BEST REGARDS

IOANNIS

Thank you for your response, professor. My inquiry seeks to explore how silicon, which can be derived from sand, can react with water under specific conditions to produce hydrogen. While sand, primarily composed of silicon dioxide (SiO₂), does not inherently contain hydrogen, I am interested in investigating cost-effective methods in which sand plays a role in facilitating or catalyzing the extraction of hydrogen.

I think it will be possible diamond bearing peridotites in west and Northwest of Iran.

I have solved many such problems using FRAC3D-VS, which is available free and has many related publications. This is just one example of many. Note: RG will no longer animate GIFs but your web browser can.

I think any mineral ore deposit can be in any tectonic environment with attention to past 28 years my field geological works.

It is the wide range of Paleozoic through Cenozoic ironstones

(1)Continental Fe deposits

(1)Eluvial –alluvial Fe placer deposits

(2)Fluvial-lacustrine and bog iron ores

(3)Claybandsand blackbands

(4)Laterite („Ferrites“), bean and karst Fe ores

(5)Residual Fe related to evaporites

(2)Marine Ironstones

(1)Oolithic ironstones(Minette-/ Wabana types)

(2)Detritaliron ore deposits

Marine Fe placer deposits

HGD

Thank you for your opinion. the rock includes fragments of volcanic and intrusive rocks like gabbro and basalt. I attached more photos.

In order for the cement to be sulphate resistant, the C3A content should not exceed 5 per cent. It is also desirable that the C3S content of the clinker should not exceed 50 %. The source of iron is iron-containing components. The source of iron can also be grinding balls and armour plates of ball mills, which are gradually eroded by abrasion during the grinding of the raw material mixture and fall into the raw material mixture. This increases the iron content of the raw material mixture for roasting.

Introducing "lots of physics" with "small data" in reservoir engineering applications is not only feasible but also potentially very effective, particularly in scenarios where data is scarce or incomplete. Reservoir engineering, which deals with the extraction of hydrocarbons from subsurface reservoirs, has traditionally relied on extensive data-driven approaches, often necessitating large datasets for accurate modeling and simulation.

Feasibility of Combining Physics with Small Data

Challenges and Considerations

Thank you.

Thank you.

Dear Gholamreza: your question should be more specific. Which metallic deposits are you talking about? Cr, Ni, PGE; or Cu-Pb-Zn-Au-Ag, or Sn-Nb-Ta, or Li-Be, or Hg-As, etc.? In general volcanic and metavolcanic rocks, tuffs and/or lavas, are progidal in volcanogenic massive sulfides, rich in Cu-Pb-Zn ores, and epithermal Au-Ag-Se-Te deposits; large stratiform gabbroic intrusions abound in magmaticm seggregation deposits, such as chromitites or PGE-reefs; most leucogranites have usually associated skarns, greisen or pegmatites riddled with rare elements, such as Li, Be, Nb, Ta, U, Sn, W and so on; carbonatites are a great source of REE, Nb, Sr and Ba. As you can see your question covers vast topics, it is like a whole course in metallic ore deposits. Regards. Sebastian.

P-wave is a compressional wave, meaning it propagates through both the solid rock matrix and the fluid within the pores. When water saturates the pores of a rock, the overall bulk modulus (a measure of a material's resistance to uniform compression) increases because water is more incompressible than air. This higher bulk modulus allows the P-waves to travel faster through the rock.

Hi Suresh - Not sure I know the precise answer because there are many carbonate surfaces in the pore system of a carbonate rock. Different types of surfaces as well as the effect of capillary pressure between the wetting and non-wetting phase in combination with the geometry of the surfaces will undoubtly affect the local thickness of the wetting film. But if you look at capillary pressure curves for carbonates (both oil-brine, air-brine and especially air-Hg capillary pressure curves) and take into account that many oil-brine and air-brine capillary pressure curves are not truly equilibrium curves (it takes too long time to reduce the water saturation due to the low relative permeability to water), then you can extract the irreducible water volume equal to the pore surface water. And if you combine the pore surface volume with the pore surface area (from tomography or BET), then you can estimate that the average thickness of the wetting phase at irreducible water saturation is around 5 nm in carbonates. This is of cause an average value and will be larger in the corners of the pore system and smaller on the flat pore walls away from the corners.

As the recorded Amott water and oil wettability clearly is a function of the maximum hydrocarbon saturation in the pore system I expect that when you reach this minimum average wetting film thickness the film will break/penetrated by the hydrocarbon phase that then may locally change the pore wall wettability and park the irreducible water in the corners.

Did this answer your question?

Most diamonds are found in Archaean rocks [0ver 2.5 billion years old]. There is no evidence of rocks of this age in western Afghanistan.

For more details of diamond-bearing rocks, consult: 'GEOLOGY – Vol. IV – Diamonds, Kimberlites, and Lamproites' by Paolo Nimis, and "Recent Advances in Understanding the Geology of Diamonds" in 'Gems & Gemology, Winter 2013, Vol. 49, No. 4.

An early exploration core should, ideally, be without a break. Things that might be missed in a 'one foot' gap include a thin volcanic tuff (for dating), or an unconformity etc. Spacing can increase with confidence and expectations.

Thanks for the comment Felipe.

Many are the aspects in the classification of igneous rocks that need to be revised. What you report is certaingly worth of note, but out of place in this thread. We need to open a new discussion topic.

Note, however, that IUGS cannot go too much in detail. No comments on the petrogenesis is required, because in this case it will be impossible to reach a consensus. We only need simple tools to give "to each rock its proper name" (as Albert Streckeisen wrote nearly fifty years ago).

Cheers,

Michele

Dear Joannis,

this is actually what is proposed. To define a rock as ultrapotassic we propose to follow the suggestion of Foley et al. (1987), i.e., K2O >3 wt% and K2O/Na2O >2, as in the scheme proposed in this thread. In addition we should consider also MgO >3 wt%, to exclude that the relatively high K2O could be simply an effect of prolonged fractionaly crystallization of K2O-poor mineral assemblage. For example, K2O-rich trachytes of the Phlegrean Fields volcano cannot be considered as ultrapotassic, because strongly fractionated melts with very low MgO.

Note that the original definitions for ultrapotassic rocks considered K2O/Na2O ratios be >3. Foley et al. (1987) reduced this ratio to 2 to include several rocks in the "ultrapotassic" family.

I did not find any word referring to "timanite" or "doiranite" in the Le Maitre (2002) book.

At the end I underline that "pyribole" is not a mineral name reccommended by IMA, so I would not quote it in the new edition of the book.

Cheers,

michele

Uranium occurs in association with almost every rock type, may be in small quantity. The most non-preferable rocks for uranium mineralisation are believed to be limestone and basic/ultrabasic rocks. Now, exception are there when you have deposits in these rocks. But off-course sandstones are the best to host good grade and large tonnes deposits.

Dear Michele and IUGS Task Group on Igneous Rocks,

About 10 years ago, as part of en effort to create a standardized nomenclature for rock classification in the Chilean Geological Survey, we reviewed the IUGS plutonic rock systematics as published in Le Maitre et al. (2002). In the area of gabbroic rocks, we found there are issues, so I support your effort to reexamine the system. Having said that, the work of Le Maitre et al. is the culmination of more than 4 decades of work by hundreds of petrologists. It is a monumental piece of work that has no parallel for the classification of metamorphic and sedimentary rocks and deposits. I believe making changes should be done thoughtfully, with great care and deliberation.

First, I wish to offer some friendly criticism of your original post. I think you have inaccurately represented the current IUGS definitions for gabbro and diorite. The definitions you cite are taken from the glossary section of Le Maitre. The glossary is a compilation of 1637 terms that include both obsolete terms and terms that are accepted for use in the IUGS system. The petrological descriptions of the accepted terms are inconcise and frequently inconsistent with the definition of the same term as expressed in the main text of Le Maitre. For example, for diorite there is no mention of the common mafic minerals in the definition of diorite where defined on page 24 of the text, and for gabbro there is no mention of accessory minerals in its definition.

Although not specifically stated in the introduction to the Le Maitre glossary, I believe that the language used there indicates that the part that precedes “now” is describing the generally accepted definition prior to the IUGS work, and that the part that follows “now” is referring to how it is NOW defined in the new IUGS system, which is usually followed by citing a diagram or section of the main text where one can find a more complete definition. This writing structure is repeated for most of the IUGS accepted terms in the glossary where the paragraph ends with a final sentence that begins “Now defined . . .”

On page 24 of the text, the separation of gabbro and diorite is straightforward and unambiguous. Both have a QAP modal composition that places them in field 10 of the QAPF diagram and a color index of >10%, but diorites have plagioclase with an An0-50 content and gabbros (sensu lato) An50-100. The use of visual aids, such as the QAPF diagram is helpful, but it is also desirable to have a verbalized version of the definition that does not require referencing a diagram, particularly for use in a glossary, for example. So, combining the information in the QAPF diagram (including information in the figure caption) and the text description of Field 10, I think a current complete IUGS definition would be:

Gabbro (sensu lato): a relatively coarse-grained plutonic rock with a QAP modal composition of <5% quartz and >90% plagioclase in the feldspar fraction, color index >10% and <90%, and plagioclase with An50-100 composition.

Diorite: a relatively coarse-grained plutonic rock with a QAP modal composition of <5% quartz and >90% plagioclase in the feldspar fraction, color index >10% and <90%, and plagioclase with An0-50 composition.

Le Maitre et al go on the explain that the definition for gabbro above actually pertains to a group of rocks that can be referred to as Gabbroic rocks or Gabbro (sensu lato), and that this group includes gabbro (sensu stricto), norite, gabbronorite and troctolite.

The text descriptions of gabbro, norite, gabbronorite and troctolite are very brief, but again, a more concise definition can be extracted from the ternary diagrams of figure 2.6 (pg. 25). For example, a complete IUGS definition for gabbro (sensu stricto), incorporating the definition above for gabbroic rocks and the information contained in the Plag-Px-Ol, Plag-Opx-Cpx and Plag-Px-Hbl ternaries would be:

Gabbro: a relatively coarse-grained plutonic rock with a QAP modal composition of <5% quartz and >90% plagioclase in the feldspar fraction, color index >10% and <90%, An50-100 plagioclase, and a Plag-Px-Ol-Hbl modal composition of 5-90% clinopyroxene, 10-90% plagioclase, <5% olivine, <5% orthopyroxene and <5% hornblende.

A similar exercise can be conducted with the other terms for gabbroic rocks in Le Maitre with the following result (to avoid repeating the definition of a gabbroic rock each time, I begin each definition with “a gabbroic rock with . . .”):

Norite: a gabbroic rock with a Plag-Px-Ol-Hbl modal composition of 5-90% orthopyroxene, 10-90% plagioclase, <5% olivine, <5% clinopyroxene and <5% hornblende.

Troctolita: a gabbroic rock with a Plag-Px-Ol-Hbl modal composition of 5-90% olivine, 10-90% plagioclase, <5% pyroxene and <5% hornblende.

Gabbronorite: a gabbroic rock with a Plag-Px-Ol-Hbl modal composition of 5-90% pyroxene where clinopyroxene and orthpyroxene are in almost equal amounts, 10-90% plagioclase, <5% olivine and <5% hornblende.

Hornblende gabbro: a gabbroic rock with a Plag-Px-Ol-Hbl modal composition of 5-90% hornblende, 10-90% plagioclase, <5% pyroxene (OPX+CPX) and <5% olivine.

Note that since the last rock type is principally composed of hornblende and plagioclase and has <5% pyroxene, the term gabbro here is used in its sensu lato meaning.

Comparing the above definitions, which I believe are a more accurate representation of the IUGS systematics presented in Le Maitre et al, to your proposed new definition for diorite, gabbro and related rocks, I must confess that I prefer the existing IUGS definitions. I see numerous problems in your proposed definitions.

For example, why do you exclude anorthite plagioclase from the definition of gabbro? Secondly, cccessory minerals, such Fe oxides, should not be part of the definition for gabbro. Your description as a plagioclase-clinopyroxene rock indicates to me that you are intending to define a gabbro sensu stricto. As in all other cases of plutonic rocks these rocks are defined modally in the IUGS system and yet only Field 10 in the QAPF diagram is cited in your definition. No mention is made to the grabbroic rock ternary diagrams where the modal composition of a gabbro sensu stricto is defined in Le Maitre.

You present various other terms such as gabbronorite, hornblende gabbro and quartz gabbro under the same definition. Each of these is a distinct variety of gabbroic rocks that I think deserves a separate treatment and full modal composition description. Also, you introduce a new term, oxide gabbro. As far as I am aware there is no plutonic rock term in the current IUGS system that uses oxides as an essential mineral for defining a rock name. Hornblende is a hydrous mafic mineral and yet your definition says hydrous mafic minerals are very rare constituents in gabbros; and so what about hornblende gabbros?

The current IUGS definition of a gabbronorite is a gabbroic rock with subegual clinopyroxene and orthpyroxene. Your proposed definition describes it as a gabbro with >5% orthopyroxene. This a would cover the entire orthopyroxene gabbro field in the Plag-Opx-Cpx ternary of Le Maitre et al, effectively replacing this term with gabbronorite. Is this change justifiable or desirable?

In our work, the issues that we discovered with the gabbroic rock classification in Le Maitre, largely concern the brevity of which the subject is treated and, in some cases, a lack of representation of some gabbroic terms in the gabbroic rock ternary diagrams of Figure 2.6. As a result, the modal definition of some gabbroic rock terms is ambiguous. This could be rectified by constructing additional ternary diagrams that cover these terms.

Additionally, there is no text description of Field 10* in the QAPF diagram, which covers quartz gabbro, quartz diorite and quartz anorthosite. So, it is unclear if quartz gabbros can likewise be subdivided into quartz norite, quartz gabbronorite, etc. A search in Google Scholar indicates that these terms are being used in the petrologic literature, so it would be helpful if the new publication covers them as well.

As stated above, I believe there is a benefit to generating a glossary of the accepted IUGS terms that does not require referencing a ternary diagram, but as a supplement to the ternary diagrams and descriptions in the main body of the text. In any case, as plutonic rocks varieties are now defined modally by their essential mineral constituents, I think is is necessary to verbalize these modal limits in any glossary definition that is provided.

Best regards,

Andrew Tomlinson

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Best regards,

Jorge

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