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Questions tagged [geochemistry]

The science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems.

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1 vote
1 answer
160 views

Does anyone know what the mineral of the year 2023 is?

I have been collecting every mineral of the year since 2012, and I have not found anything on last year's mineral.
4 votes
1 answer
46 views

What is a good definition for "lattice bound" and is iron within octahedral sites of illite considered lattice bound or interstitial?

The title pretty much says it all. I cannot find a satisfactory definition of "lattice bound", just a number of examples of it being used in literature. For example, in this paper about ...
5 votes
2 answers
787 views

Where does molecular hydrogen in the atmosphere come from?

This figure from Wikipedia's Atmosphere of Earth shows a hydrogen fraction of 0.000055 percent by volume. Question: Where does molecular hydrogen in the atmosphere come from? Does this come directly ...
0 votes
0 answers
9 views

Dependancy of acid strength and volume to the column size: Column Chromatography

Is there a way to theoretically estimate the changes to be made to the acid strength and volume when the length and the inner diameter of the column capillary and hence the resin volume are changed? ...
4 votes
1 answer
68 views

Simple explanation of what "preferential lattice expansion due to excessive magnesium adsorption", means

In the context of crystal growth, particularly saddle or baroque dolomite development, what does "preferential lattice expansion due to excessive magnesium adsorption" mean in practical ...
4 votes
2 answers
140 views

Likely air composition in cave only accessible from underwater?

I recently stumbled upon images of the Cosquer cave in France, famous for being a recently discovered Paleolithic decorated cave. The entrance to the cave now is more than 30m below the waterline and, ...
2 votes
5 answers
7k views

Are fossil fuels really formed from fossils?

Hydrocarbons have been found in great abundance elsewhere in the solar system where there is unlikely to be evidence for life past or present. No fossils involved. Petroleum and natural gas wells ...
11 votes
2 answers
3k views

What is the Calcite Compensation Depth and what is its significance for carbonate deposits?

What is the Calcite Compensation Depth (CCD) and what is its significance for carbonate deposits?
3 votes
0 answers
35 views

Does each volcano have a fingerprint?

Thinking about arc volcanism in a region, and there are two neighboring composite volcanoes 50 km apart from each other. Do you expect any differences about their products (lavas, pyroclastic deposits)...
2 votes
1 answer
435 views

Stratigraphy of limestone applied to the Great Pyramid of Giza

The Great Pyramid of Giza is made from blocks of limestone quarried from the Giza plateau. The pyramid is composed up of about 200 layers, with individual blocks varying in thickness from 20 to 60 ...
2 votes
2 answers
355 views

How is the difference in crust and mantle composition explained?

We know that the composition of the crust is SiAl and SiMa and the one of mantle is mostly ophiolites, but why? Which are the geological processes that make this difference exist?
5 votes
2 answers
238 views

Why does calcium occur together with felsic rocks and magnesium with mafic rocks if calcium is denser than magnesium?

Felsic rocks contain a lot of sodium, potassium and calcium (and a great deal of aluminum), while mafic rocks consist of a lot of magnesium with iron.... Why is this? Why is magnesium (z=12) in the ...
4 votes
1 answer
5k views

What is the difference between chalcophile and siderophile elements?

As it is described (W. M. White, Geochemistry): Siderophile elements have an affinity for a metallic liquid phase and chalcophile elements have an affinity for a sulfide liquid phase. What ...
4 votes
1 answer
130 views

Why don't most organisms use magnesium in their shells and bones if it is lighter and more common than calcium?

Magnesium is one of the most abundant elements in the Universe and on Earth.... So why is it not used in the forms of Magnesium Carbonate and Magnesium Phosphates (Hydroxyapatites, etc.) to make ...
4 votes
1 answer
180 views

Why does decreasing surface alkalinity increase surface pCO2?

According to Takahashi et al. (1993), pCO2 (partial pressure of CO2) in the surface ocean changes due to 4 surface variables: temperature, salinity, total carbon (dissolved inorganic carbon, DIC) and ...
4 votes
2 answers
192 views

Why are ionic bonds considered the "dominant" type in minerals?

I'm just starting out in geology and I keep reading that ionic bonds predominate among minerals. However, the majority of minerals are silicates and the silicate ion has covalent bonds, so they ...
3 votes
1 answer
197 views

What is the reason that some elastic constants are negative?

In this table of elastic constants, indices m = 1 and n = 4 result in negative values. What could the reason be?
1 vote
0 answers
51 views

Estimation of rare earth elements in the SUAC complex

I am currently competing in a case study competition a part of which has asked us to estimate the amount of Nd, Pr, and Dy in the SUAC complex (Sung Valley Ultramafic-Alkaline-Carbonatite) in electric ...
1 vote
1 answer
272 views

Interpretation of Phanerozoic CO2 levels graph

I used to talk with a family friend who often sent me links to Nobel Prize winners, claiming that climate change is a myth. Last week, we had a disagreement over a link referencing a Nobel Prize ...
2 votes
2 answers
259 views

Is this why oceans are salty?

From noaa.gov's Ocean facts: Salt in the ocean comes from rocks on land. The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air. This causes the ...
1 vote
0 answers
55 views

Co variance of isotopes in geochemical amplications

I recently heard that the d98Mo isotope is not different from the d238U isotope in redox processes e.g. in black shale events. But I can't find any evidence except the figure from Zhang et al. ...
3 votes
1 answer
109 views

If the universe (and our galaxy) has about twice as many oxygen atoms as carbon ones, why does Earth have 300 times as many oxygen atoms as carbon?

A (relatively) recent 'Sky & Telescope' magazine feature story mentioned how little carbon the Earth has, and how some scientists' models predict we should somehow have even less.... So I looked ...
10 votes
5 answers
7k views

Are there minerals which are not been found on earth but which are still possible to exist?

On Earth we find many kind of minerals, a lot of them are silicates. How much different kind of minerals would there be on Earth? But are there Fe minerals found in meteorites which do no occur on ...
16 votes
3 answers
1k views

What processes produced the basalt columns of the Giant's Causeway?

The Giant's Causeway is, according to the Wikipedia page was formed during during the Paleogene Period, Antrim was subject to intense volcanic activity, when highly fluid molten basalt intruded ...
7 votes
2 answers
164 views

Why is hydrogen formation in serpentinisation an exothermic reaction?

In the process of serpentinisation, protons act as oxidising agents for ferrous ions, which results in the production of dihydrogen gas. How is that possible? Dihydrogen being a strong reductor, I ...
3 votes
0 answers
77 views

Can $\ce{CaCO3}$ shells contribute to $\ce{CO2}$ emissions in volcanoes within subduction zones?

CaCO3 dissolves below the Carbonate Compensation Depth (CCD). However, this paper suggests that some CaCO3 can exist below the CCD. My question arises from a discussion in this answer. The question is ...
4 votes
2 answers
269 views

Why is there gold in the earth's crust?

I would naively assume that when the earth was formed and still molten, all the heavy stuff such as gold would have sunk to the centre, so almost nothing would remain in the earth's crust where humans ...
11 votes
2 answers
260 views

What oxidised the soil on Mars?

What exactly was it in the ancient Martian atmosphere that made it red? Was it water, molecular oxygen or something else?
13 votes
3 answers
7k views

What is the white coating "patina" we often see on deposited chalcedony/agate?

Me and some of my friends were wondering what exactly is the white coating we can see on chalcedony that has been deposited by a river during quartenary (and so the original material is damaged and ...
1 vote
1 answer
43 views

Is it possible that the rainbow sand dunes in Death Valley, California were formed by some massive mining in the ancient past? [closed]

I know there is a mainstream answer that thinks the rainbow sand dunes they be explained geologically... I just want to know if it's possible to form those colors and those dunes from mining? And if ...
1 vote
1 answer
74 views

Does granite and basalt behave differently in different atmospheric pressures?

We all know that the oxygen levels increase and decrease as well as the temperature, so I believe it's safe to assume atmospheric pressure changes as well... And since granite and basalt are formed ...
2 votes
2 answers
4k views

How do I convert an element measurement to oxides?

So, I did some measurements in ICP-OES and the results were given to me in elemets. However, I need to convert the results to oxides. After some googling I found out that I need to use simple ...
26 votes
2 answers
3k views

Why does phosphate rock contain uranium?

I have been doing some research on the issue of phosphogypsum pollution. Phosphogypsum is a waste by-product formed with the "wet process" method of extraction of phosphoric acid out of ...
45 votes
2 answers
12k views

Why is NaCl so hyper abundant in the ocean?

Why is sodium chloride far and away the most abundant salt dissolved in ocean water? Its two constituent ions do have a very high frequency in the crust of the earth, but they are far from the most ...
4 votes
0 answers
32 views

Reason for finding low boron levels in clayey soil with high organic matter?

I've read from various University Extension sites (e.g., here and here) that boron levels would be deficient in sandy soils with low organic matter. This would suggest that boron levels would be ...
3 votes
0 answers
189 views

Causes of high calcium levels in sandy alluvial soils

When soil calcium is high: High levels of soil calcium may be expected when there is substantial calcium carbonate bedrock from which the soil has weathered. Calcium levels can be high in agricultural ...
2 votes
0 answers
18 views

Searching for Geochemical Threshold for PTE's of Spain

Where can I find a table with the geochemical threshold for potentially toxic elements in the soils of Spain? I only have seen a decree with organic compounds for Spain.
15 votes
1 answer
844 views

Does the heating of the oceans due to greenhouse effect negate the acidification due to increased CO2 levels?

As I understand, the dissolving of carbon dioxide leads to increased acidification of the oceans, and thus increased atmospheric CO2 levels would lead to more dissolution in the oceans and thus ...
2 votes
0 answers
38 views

Under which conditions would you see the MOST lake effect precipitation?

It's well known that the Great Lakes produce large amounts of precipitation in the Fall. When cold polar air moves over the lakes it causes large amounts of relatively warm moist air to rise, ...
12 votes
1 answer
2k views

Why do Volcanoes give out so much Sulphur Dioxide and Carbon Dioxide?

From my understanding, the mantle is in a highly reduced state, so I can't understand why a volcano would give off a highly oxidised gas such as sulphur dioxide. Carbon dioxide is too an oxidised gas ...
1 vote
0 answers
39 views

Help me find a certain type of crystallographic notation

I was looking through wikipedia a few weeks ago while half asleep, reading articles about rocks and their chemical compositions. I then came across a certain crystallographic notation which I had not ...
2 votes
1 answer
655 views

Why is silver found mainly in lead

Apparently according to the Parkes Process silver is 3000 times more soluble in zinc than in lead. So why is it that most silver is obtained from galena? Edit: “ Silver mainly occurs as a contaminant ...
2 votes
0 answers
26 views

Calculate original volatile content of a degassed mineral

A lunar apatite sample has a relatively low OH content of 5 ppm, but a an elevated D𝛿 of 11,000‰ (vs. SMOW). Assuming that water had an original figure of around -100‰ or so, how do I estimate the ...
0 votes
1 answer
66 views

Is experience abroad important for your career?

I'm just finishing my Bachelor's degree in Geochemistry at a German university and will soon start my Master's degree, but I've been wondering for a few weeks whether a stay abroad (1 semester or even ...
1 vote
1 answer
479 views

What does fugacity mean in the context of geology?

I am reading about water in the Lunar mantle, however it mentions fugacity a lot. What does it mean in this context?
4 votes
2 answers
41 views

Calculating/estimating volatiles based on other representative samples

I am currently working on a set of geochemical data representing calc-alkaline igneous intrusions from central Canada. The samples were analyzed in ~2013-2014. These samples have been tested for LOI ...
3 votes
2 answers
116 views

Where is basalt in the Goldich dissolution series?

In relation to this experiment: https://www.remineralize.org/rem_publications/action-of-microorganisms-in-basalt-powder/ It is said that applying basalt rock dust to soil can improve soil fertility ...
10 votes
2 answers
1k views

Composition of Martian Crust

Does the composition of the crust of Mars roughly correspond to that of the crust of Earth. That is, is the elemental abundance in decreasing order silicon, oxygen, aluminum, etc.?
4 votes
0 answers
80 views

Kinetic or equilibrium fractionation from 2H and 18O in evaporation and condensation?

Is the isotope fractionation that occurs during evaporation of surface water equilibrium fractionation or kinetic fractionation? I mean, evaporation can be described by Rayleigh fractionation, but I ...
1 vote
0 answers
17 views

What chemical or physical parameters altered during the usage of buffered versus unbuffered extractant for leachability of a soil or sediment?

Toxicity characteristic leaching procedure (TCLP) is an extraction method to simulate a soil or sediment leaching. The method employed two extraction fluids - one is a buffered solution of acetic acid ...

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