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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129 views

What does 5,000,000 tonnes of CO2 look like?

Reading a news article Probe after Gorgon releases millions of tonnes of greenhouse gas, I am confused. CO2 is a gas, right? Gases are not very dense, right? So what does 5MT of the stuff look like?...
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220 views

Carbon's role in ocean acidification

This might seem like a basic question, but I'm a little confused about the effects on ocean acidification of different carbon compounds. I have heard that increased levels of carbon dioxide in the ...
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1answer
198 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 ...
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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/...
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1answer
678 views

Please help in understanding redox buffers

I'm trying to gain a firmer conceptual understanding of how redox buffers work in petrology, specifically how oxygen fugacity influences mineral crystallization. While I understand the mathematical ...
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Reason for higher content of Iodine and Copper than Iron in Seawater?

Does mineral weight contribute to the prevalence of minerals in seawater? Why is there five times more copper in seawater than Iron? Why is there 4000 times more strontium in seawather than Iron, ...
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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 ...
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1answer
375 views

Is the iron on Earth's crust a leftover of the Iron catastrophe, or it was brought back by volcanoes?

When pondering the hypothesis of the Iron catastrophe, that seem to be widely accepted nowadays. It surprises me that currently the crust still contain a significant amount of Iron (5.6% in weight). ...
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1answer
293 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 ...
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65 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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34 views

Formation of dolomite

What are the kinetic barriers to dolomite precipitation? Does it precipitate out in solution as quickly as Calcite does?
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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.
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Pyrite oxidation

How much pyrite has to be oxidized to produce a sulfate concentration of 15 mM? If the solution initially has a pH of 8, roughly what would the pH drop to if there is no buffering of acidity?
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1answer
82 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 $PM_{2.5}$ ...
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1answer
579 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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2answers
113 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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1answer
163 views

What controls the acidity of the ocean?

I have learned that: coral reefs are made up mostly of calcium carbonate coral reefs are mainly distributed in the tropical zone The calcium carbonate will be decomposed in the reaction as ...
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144 views

Mass balance for calculating mantle composition

I've seen some problem sets given without answers / solutions regarding how to calculate the composition of the mantle given solar composition (and assuming the same would apply to the Earth). For ...
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1answer
52 views

Effect of reducing conditions on melting point

I've been reading a paper(*) looking at the deep carbon cycle and it mentions a key process that the authors refer to as "redox melting". According to the paper, reducing conditions increase the ...
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2answers
169 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 ...
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2answers
287 views

Analyzing composition of a mineral using SEM

If I have a mineral in which I did a SEM analysis on and got the data (elements and their wt% with Std. Dev., MDL, atomic % oxide % and k ratio) how would I go about quantifying the sample's ...
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139 views

Dolomite and calcite precipitation

In an engineered wetland, there is groundwater flow from an aquifer with a chemical composition that is rich in magnesium, calcium and sulfate. We are finding that the aquifer is consistently ...
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2answers
123 views

Limitations on mineral precipitation from solution

If the solubility constant for a mineral is exceeded and, thermodynamically, a mineral is favored to precipitate in solution, are there any factors that may limit this from happening? Perhaps kinetics?...
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1answer
652 views

Gypsum saturation index

I did some geochemical modelling and found groundwater samples I have are saturated with respect to the mineral gypsum. I need some help with interpretation, more information is given below. The ...
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57 views

calculation monocationic elements

How to calculate of the number of monocationic millimoles? If I have concentrations of: $SiO_2$, $TiO_2$, $K_2O$, $MgO$, $MnO$, $Na_2O$, etc. How can I get $Na^+$, $Mg^{2+}$, $Mn^{2+}$ ..? This is ...
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1answer
51 views

Saharian calima dust, apart of Fe2O3 does contain FeO?

It is repeated often that Saharan calimas are fertilizing often Atlantic ocean. But I suppose that most of Saharan dust contains Fe2O3 and not FeO. Am I right?
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3k 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 ...
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231 views

Abiogenesis: Formation of Lipids from Montmorillonite

I have been really interested in scientific hypotheses regarding abiogenesis, particularly the lipid-world hypothesis. However, I could not find information on the chemical pathway that leads to the ...
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1answer
614 views

Crystallization path of diopside-wollastonite-silica systems

Can someone please explain to me (or give a source) how the crystallization diagram of the diopside-wollastonite-silica system looks. I am a new learner of geology and trying to learn ternary systems.
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1k views

Where can fluorite be found on Long Island, New York?

I'm interested in fluorite (Since Fluorine is my favorite element, and I wanted a sample of it, even if bonded, but I don't want to buy it; that would be no fun), and I'm curious if it can be found on ...
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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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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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Does perchlorate(rocket fuel) and jet fuel make the salt and ground water near Cape Canaveral dangerous?

I've gotten into paddle surfing and I'm looking for a place to live and surf. I've been looking at an buying a condo in Cocoa Beach because of it’s proximity to Orlando and Cocoa’s decent but ...
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3answers
1k views

Can you measure BOD/COD real time using any sensor?

There is a requirement to measure BOD/COD in a wastewater treatment plant in real time. Is it possible? And if so are there any sensors available in the market for it? COD: Chemical Oxygen Demand BOD:...
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2answers
416 views

What fraction of Earth's crustal material survives the supercontinent cycle?

I know that things are not as simple, but for the sake of argument I'll assume a supercontinent cycle of $\sim$400 Myr periodicity is active on Earth. If that is the case, then my naive ...
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1answer
449 views

What “g” would be needed to keep helium on Earth?

I know that helium is a very light and rare gas on Earth because Earths gravity is not strong enough to keep it. Instead, helium and hydrogen are rising through the atmosphere and escape into outer ...
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1answer
1k 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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1answer
2k 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 ...
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1answer
82 views

What negative side effects would occur if silicate mining were used to artificially lower atmospheric CO2 concentrations?

As one half of the naturally occurring Carbonate–silicate cycle, carbon dioxide is naturally removed from the atmosphere by the chemical reaction: CaSiO$_3$ + 2CO$_2$ + H$_2$O → Ca2+(aq) + 2HCO$_3$-(...
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459 views

Diamond at the core of Jupiter

Arthur C. Clarke, who correctly guessed there would be liquid water on Europa, posited a diamond core for Jupiter. Is this possible?
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389 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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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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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 ...
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1answer
101 views

Dolomite in deep-water environment

Is it possible that dolomitization occur in deep-water environment? If it possible, how?
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4k 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 ...
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Weathering of silicates

I am trying to find a relationship between the silicate-rich rocks weathering products. For example I've found information regarding gabbro weathering in which, according the consulted source, in 100 ...
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1answer
181 views

Ions & elements, which is the correct terminology to use when discussing chemical compounds in Earth Science?

Different textbooks use different terminologies when discussing the same chemical compounds, for example when discussing the minerals... Elements / Compounds Sulfide minerals consist of metallic ...
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1answer
154 views

Melting basalt on the lunar surface - what would the resulting material be like?

The idea is to melt the fine-grain portion of basalt regolith using a large Fresnel lens, and let it cool to a solid. The lens would track along a tamped bed of material leaving a molten puddle ...
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1answer
130 views

How much coal does it take to generate oil?

I'm going to be doing a presentation for grade school children, and I'd like them to get a feel for how much source rock it takes to make oil. It takes about a 10 foot layer of swamp debris to make ...
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85 views

Would you see a correlation between detrital zircon age and grain shape?

If one was to quantify the shape (particularly roundness) of detrital zircon grains, would there be a correlation between the age of the detrital zircon grains and their shape? For example, if the ...