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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6
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1answer
86 views

Mars maar craters explosive style formation gravitational effect

"Maars usually form when magma rises within a fissure and interacts with groundwater. If groundwater ceases to interact with magma at times during the eruption, continued magma ascent to the surface ...
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2answers
482 views

Age of fossils found in rocks

I have heard the claim by creationists that geologists date rocks by the fossils they contain and date fossils by the rocks in which they are found. This supposedly invalidates radiometric ages ...
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3answers
12k views

Why silicon is abundant in earth surface?

What is the reason for having silicon in so large quantity on earth surface?
5
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1answer
319 views

Why is my ♦ hammer (i.e. diamond) so durable, but it can burn? [closed]

For those confused about the title, there's a joke that every moderator has a "diamond hammer" (diamond from the little by the username). In a chat discussion, it ...
5
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1answer
204 views

What are the cubic formations found inside Larimar gemstones?

I recently noticed what appears to be common cubic formations just beneath the surface of Pectolite (Larimar) gemstones. They quite resemble transparent sugar sprinkles. Each formation isn't perfectly ...
5
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2answers
113 views

Molten salt seas on the future Earth

As the sun gets brighter, the oceans are expected to evaporate by the next billion years or so (the vapor slowly gets stripped off into space). The salt, which is less dense than most rocks, will be ...
5
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1answer
394 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.?
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201 views

What is the CI chondrite concentration of REEs/rare metals, in ppm/grams per ton?

I am researching the abundances of rare earth elements and rare metals in meteorite samples, because I want to investigate the notion that asteroids represent abundant stocks of rare resources. The ...
5
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2answers
246 views

Marine and freshwater geochemistry

As rivers flow into the sea, rivers contain a high concentration of calcium and carbonates, and a low concentration of sodium and chlorine, and for marine water it is vice versa. How come?
5
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1answer
298 views

Difference between pyrite oxidation and dissolution

I've seen papers use oxidation and dissolution of pyrite. Are these two processes the same? I was always under the impression that pyrite does not dissolve easily. What is the difference between ...
5
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1answer
83 views

What controls the tendency of trace elements in different particle size fractions?

Trace element atmospheric particles are introduced from different sources, with both anthropogenic and natural origins. By analyzing the concentration levels of 18 elements in samples of $PM_{2.5}$ ...
5
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2answers
115 views

Sulfate salts of magnesium and sodium

What concentrations of magnesium, sodium and sulfate are needed to precipitate solid MgSO4 and Na2SO4 (let's say evaporation is occurring in a system) I'm assuming probably really high because they ...
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0answers
66 views

Chloride and evaporation

I have a layered aquifer with water that contains high concentrations of calcium and sulfate (~400 mg/L Ca2+, ~1300 mg/L SO42-), at 50 cm below ground surface (bgs), 250 cm bgs and 300 cm bgs. The ...
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65 views

Why is seawater saline? [duplicate]

Why is seawater saline and not fresh? Could it be saturated with anything else, like, say, dissolved metal?
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1answer
801 views

What are the implications of the recent discovery that huge oceans exist close to the mantle of the Earth? [duplicate]

I was of the notion that as we get deeper into the Earth, it gets hotter and hotter. If so, how can there be huge oceans (they seem bigger than our Pacific) exist at such a place? If so, what are the ...
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2answers
183 views

Upon breaking apart andesite, what do you get?

I'm aware that andesite consists of about 60 percent silica and as for minerals, pretty sure it's usually pyroxene and plagioclase. What form would these take on if they were to be separated? ...
4
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1answer
11k views

What is the difference between N-MORB, E-MORB and OIB?

What are the differences between N-MORB, E-MORB and OIB with regards to: Tectonic setting Geochemical features There are several types of basalts, but I can't find a clearly explained article.
4
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1answer
170 views

Why is the concentration of highly siderophile elements so uniform in the mantle?

The plot above is about the concentration of siderophile elements in the terrestrial mantle. From the logarithmic plot, we can deduce that the concentration of highly siderophile elements is quite ...
4
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1answer
586 views

Why is uranium only in the crust, really?

As I know, uranium is currently thought that it is mainly in the crust and not in the core or in the mantle. The reason for that it is a siderophile element which means it won't be solved in molten ...
4
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3answers
730 views

What natural phenomena increase stratospheric ozone?

Most of us know that the ozone layer gets depleted due to green house gasses and other factors. Which made me wonder, is there any natural phenomenon that causes an increase in ozone?
4
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1answer
288 views

What are the formula weight and gram-formula unit (gfu)?

I'm reading Shaw's "Trace Elements in Magmas" and in his page 16 he writes the following: ...It is necessary to look at the relationship between $c_i$ and $x_i$, i.e. the weight and molar ...
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1answer
683 views

Is porphyritic texture always indicative of a 2 stage cooling process?

Is porphyritic texture always indicative of a 2 stage cooling process? Can't the phenocrysts and groundmass be formed at the same time depending upon the chemical constituents forming the rock? The ...
4
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1answer
2k views

How can I normalize this chemical analysis to a mineral with 3 cations?

$\ce{FeO}$ = 70 wt% $\ce{TiO2}$ = 30 wt% The molecular weight given of $\ce{FeO}$ = 72, and the mw of $\ce{TiO2}$ = 80. The first step I did was divide each wt% by their molecular weights to get a ...
4
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1answer
74 views

The effect of CO2 concentration on the pH of the ocean

I'm confused about how increased $\ce{CO2}$ concentration in the atmosphere affects the pH of the ocean. The increase in $\ce{CO2}$ concentration means the pH of the ocean will decrease (by several ...
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2answers
231 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 ...
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1answer
2k views

Does ground-to-cloud lightning create crystals as well?

I've read that cloud-to-ground lightning can create fulgurites. Does ground-to-cloud lightning also create crystals within the earth as it surges through the minerals?
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2answers
143 views

What are the natural causes for methane formation?

Natural gas is mostly made of methane ($\ce{CH4}$). Methane can be produced as a result of microbes eating organic matter. But can it also be naturally formed without any assistance from organic ...
4
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1answer
261 views

Source of sub-surface ringwoodite water

I was reading about the discovery of vast amounts of water locked up in ringwoodite (see here). The authors of the study seem to suggest that previous ideas, involving water deposits being delivered ...
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2answers
175 views

Relative dating of granite pluton

In selecting a sample for age-dating of a granite pluton, which site is a better site to collect a sample from, the centre, top or side? Why was this site a better choice? Which dating method would ...
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2answers
570 views

Looking for a complete table of minerals for a database

I am building an open source spatial geochemical/geological observational database for mineral exploration. I need to fill the mineral lookup table. Where can I find a complete list of all minerals ...
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1answer
53 views

Phosphate in the oceans, does it tend to bond with sodium?

Phosphate has a major role in biology and the biosphere. In its "abiotic" form, floating around in the oceans, lets say marine oceans to be specific, does it tend to be in the Na3PO4 form? ...
4
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1answer
72 views

Are the precious metals (silver, gold, platinum) present everywhere throughout the Earth's crust at least in the trace quantities?

Do some rocks, soils, sands or waters exist that contain fewer than one atom of gold per cubic meter or tonne of their mass?
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1answer
81 views

Employment of Volcanologists and Petrologists

What industries or government departments hire volcanologists and igneous petrologists/geochemists in the United States?
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1answer
101 views

Relationship Between Ratio of Atmospheric Gases and Ocean Gases

A version of this question was posted in Chemistry SE and Worldbuilding SE but I've been told it wasn't appropriate to either SE. I was told to give this SE a chance. If you think it doesn't belong on ...
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0answers
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What causes a change in composition from basanite to nephelinite?

Can the change in composition from basanite to nephelinite (i.e. increasing alkalis with decreasing SiO2) be explained in terms of fractional crystallisation, or only by a decreasing degree of partial ...
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100 views

What reactions change seawater composition in hydrothermal systems?

Reactions in ocean floor hydrothermal systems are a significant contributor to the mass balance of several major elements in the oceans, in particular magnesium, calcium, sodium, potassium and sulfate....
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30 views

Can humidity changes induce stacking-sequence changes?

My understanding is that some minerals with layered crystal structures will reversibly absorb water with changes in humidity. Are there any minerals where this reversible absorption leads to a ...
4
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1answer
147 views

Has Earth's atmosphere lost mass throughout the geological ages due to biological $\small\sf{CO_2}$ fixation?

Stromatolites and other organisms have been storing $\small\sf{CO_2}$ in the form of $\small\sf{CaCO_3}$ throughout the geological ages, forming extensive limestone deposits scattered across Earth's ...
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2answers
120 views

Is there a risk with putting out smouldering underground coal reserves? [closed]

According to this Discovery News video about Centralia Pennsylvania and other underground coal fires, there are many smouldering underground coal reserves making the land above it uninhabitable to ...
3
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4answers
209 views

Why is mass fraction always abbreviated wt% and not ma%?

In most geology papers, major elements chemical analyses are expressed as mass fraction of oxides, i.e. SiO$_2$ 64.2 wt%, K$_2$O 4.3 wt%, etc. The mass fraction unit is always abbreviated as "wt%". ...
3
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1answer
76 views

Is it possible to form a diamond-sapphire hybrid?

I've been looking into diamonds recently and was made aware of diamond hybrids where diamond is grown on either a seed diamond or cubic zirconia. I was wondering if it would be possible to do ...
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2answers
1k views

What exactly are enantiotropic and monotropic polymorphic transitions?

Recently, I've been studying the subject of polymorphism and met two important concepts, the monotropic and enantiotropic polymorphic transition types. However, I can't really seem to grasp the ...
3
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1answer
833 views

What is the difference between mineral groups and series?

It seems to me when reading about minerals, groups and series are spoken about interchangably in similar types of contexts. Is there a difference? If so, what?
3
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1answer
73 views

Relation between molecular mass and retention of a gas on a planet

An Introduction to Our Dynamic Planet under section 2.4 "The origins of the atmosphere and hydrosphere"(Page 80) says on the topic of gases escaping from our atmosphere as: Different gases ...
3
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1answer
265 views

Why is Thermohaline Circulation (THC) pivotal to life on Earth?

Thermohaline circulation (THC) is an instance in nature in which oceanic fluctuation of amassity, temperature and sodium matter is observed on a global scale. It is compared to and sometimes called ...
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1answer
35 views

Is CO2 in the Pacific Ocean depleted or enriched in Carbon-13 compared to the Atlantic, and why?

Due to thermohaline circulation, the Pacific water is more 'aged' so there is a higher amount of total dissolved inorganic carbon (e.g. CO2) in the deep Pacific when compared to the Atlantic. However, ...
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2answers
88 views

Iron-nickel phase in pallasite meteorites

I have recently been learning and researching about meteorite types and classification. Pallasites are mainly composed of a 'solid-solution' of olivine crystals and an iron-nickel alloy. My question ...
3
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1answer
581 views

Saturation Index clarification

I have a problem with my project and I was hoping I would find some clarification. I did some modeling with phreeqc to calculate saturation indices and found that calcite was saturated in an ...
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1answer
4k 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 ...
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0answers
56 views

Sulfate reduction

I read a document in which the authors stated "Sulfate and sulfide ( bisulfide and dihydrogen sulfide) both exist within a system just in varying proportions, and aqueous speciation is dependent on Eh/...