Questions tagged [minerals]

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22
votes
3answers
22k views

Where can obsidian be found?

Where is obsidian found? Is it typically found on the surface or underground? If underground, how far under (meters or feet would be perfect)? Also, is it found everywhere on Earth, or just in areas ...
17
votes
5answers
32k views

Why do gold deposits form only in certain areas of the earth?

In the map above you can find that most elements are spread evenly throughout Earth's crust and that they are available all around the Earth. However, gold can only be found in certain areas of the ...
17
votes
2answers
16k views

What determines a mineral's hardness?

Mohs Hardness Scale is basically a measurement of the hardness of a material, or more specific, a rock or mineral. But I have never been able to figure out why some minerals are harder than others.
16
votes
3answers
28k views

How do geologists find ore deposits?

From my research, there is lots of information on how to extract ore, but I can't find any information on how these ore deposits are found in the first place, apart from 'looking for surface ...
16
votes
2answers
19k views

Why does the colour of amethyst fade if exposed to too much light?

It is well known that the purple hue that is characteristic of the amethyst quartz ($\ce{SiO2}$) will fade if the crystal is exposed to light for a prolonged period of time. What is the underlying ...
14
votes
3answers
6k views

How and where do double-terminated crystals form?

How and where do double-terminated crystals form? Most terminated crystals form by 'growing' out of a rock. Which causes one side to be flat,(or whatever the shape of the rock it 'grew' out of was ...
12
votes
2answers
2k views

Is it possible for a natural fluorescent mineral to glow from the sun's rays?

I have been searching certain fluorescent minerals, such as Andersonite, and all websites are saying how the mineral will glow if exposed to Ultraviolet light. Does enough ultraviolet light come ...
11
votes
1answer
2k views

Why do most opal deposits occur in Australia?

According to the Wikipedia page about opals, this hydrated amorphous silica based gemstone is most commonly found in Australia, with according to the page, over 90% from Australia. Opal from Coober ...
10
votes
1answer
5k views

What kind of minerals have no cleavage plane?

Why does quartz have no cleavage plane and halite does? What do I need to know about the specific mineral so that I can decide whether it has cleavage or not? I need some kind of rule.
9
votes
1answer
336 views

What is the geologic origin of Cryolite, and could there be more?

Cryolite is a mineral of aluminum (Na$_3$AlF$_6$). The only known natural deposit was found in Ivittuut, Greenland. It was mined from 1854 to 1987 and yielded 3.7 Mt of Cryolite ore. Basically my ...
8
votes
2answers
1k views

What is meant by phase-change in mantle?

Phase transition usually means changing from liquid to solid phase. But in geology literature we come across transitions from one mineral to other mineral. For example olivine-spinel transition at 410 ...
7
votes
1answer
2k views

How do hematite and magnetite form?

I want to understand the conditions under which hematite $\ce{Fe_2O_3}$ and magnetite $\ce{Fe_3O_4}$ form in nature. The linked Wikipedia articles explain various conditions under which they form, but ...
6
votes
1answer
966 views

Plotting a mineral stability diagram

I'm trying to figure out how to plot the stability of 4 minerals — $\ce{CaCO3}$, $\ce{CaSO4}$, $\ce{CaMg(CO3)2}$, and $\ce{CaMg3(CO3)4}$ — with axes of $\mathrm{ln}\,a_{\ce{Mg^{+2}}}$ vs $\mathrm{ln}\,...
6
votes
2answers
227 views

Can I just walk around Greenland with a UV light and find rare Earth minerals on the ground?

The NPR.org news article and podcast Greenland Is Not For Sale. But It Has The Rare Earth Minerals America Wants is interesting, and it includes a few large GIFs (too large to post here) that appear ...
6
votes
2answers
2k views

Why are most minerals so rare?

There are 4,660 known minerals, so why are most of them so rare? Is it to do with the structure of minerals?
5
votes
1answer
252 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
votes
1answer
2k views

Why is streak different from color?

Many minerals have a streak that's surprisingly different from it's outward color. Why is this? What causes the optical properties to change if the mineral is powdered? Thanks!
5
votes
2answers
386 views

Muscovite with pleochroic halos?

Is it possible to find pleochroic halos in muscovite ? I would have said that it must be biotite (also, in PPL it is brown!), but then.. why does it have interference colors so similar to muscovite ? ...
5
votes
2answers
193 views

Is this classification of mineral formation environments correct?

I am writing an app for students that consist in 180 sheets of the most common minerals on Earth's Crust. One of the fields of the sheets is environment of formation. It is important to me to ...
5
votes
2answers
3k views

How does quartz form in calcite veins?

This question might be a bit silly, but I have to ask since I am very curious and I did not find any good answer. I visited two places, where quartz crystals (var. smoky quartz) occurs - and both ...
5
votes
2answers
676 views

Were all of Earth's minerals created before Earth's formation, during, or after?

I've heard that during the accretion of proto-planets that formed the earth, 60 minerals were created through the reactions of atoms and molecules in the nebula. Do these first minerals still make up ...
5
votes
1answer
144 views

Strange coating in old lime mine shaft

Near Prague,Czech Republic is old lime mine. Most of it is closed but one short transport tunnel under one hill is publicly accessible. Tunnel has profile around 2,5x2,5m and it's slightly bended and ...
5
votes
1answer
828 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
votes
2answers
654 views

Mining iron or metals in nature

Upon watching all the videos from PrimitiveTechnology on Youtube, I've decided I would try something similar. I know how to make clay and use this to make an oven. I also know how to make charcoal. ...
5
votes
1answer
543 views

How does palingenetic fusion occur in rock?

As far as charnockites are concerned, granitic charnockites are formed due to palingenetic fusion and metasomatism, while granulitic charnockites are formed due to high grade metamorphism. When I ...
5
votes
2answers
130 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 ...
4
votes
4answers
100 views

How is it possible for rocks to be trapped within another type of rock?

More specifically, I would like to know how the rocks in these pictures have formed: If this is because magma has melted and trapped the other rocks inside, do they have a different melting point ...
4
votes
2answers
149 views

Are there minerals that can't scratch each other but have different hardness on Mohs scale?

So I was reading here that Mohs scale is not transitive and therefore could not overcome the comparative phase in order to be turned into a measurement procedure. As it is written in the webpage, &...
4
votes
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
votes
2answers
118 views

Database of mineral with images for a neural network application

I'm diving into data science and I'm looking for a complete database of minerals. I downloaded the csv file from http://rruff.info/ima/ . It contains 5516 lines of data but it does not have images or ...
4
votes
1answer
32 views

Why is Melanterite white or colorless?

I've read that melanterite (FeSO4*7H2O) is colorless or white and gets to be green to blue with increase in Cu2+ impurities. But from my chemistry experience I know that iron sulfate is green when in ...
4
votes
2answers
3k views

What are the most common minerals at the Earth's surface?

I know how to find out the first few most common minerals, and I know how to find a list of 6800 minerals that one geologist found as a microscopic grain in this one meteorite. I can't seem to find a ...
4
votes
1answer
40 views

Is there any mineral that survives hard degree metamorphism?

When a protolith enters in metamorphism, the minerals transform in other new stable minerals while the pressure and/or temperature increase. Is there any mineral that would not be affected by a high ...
4
votes
1answer
104 views

History of the Arctic Ocean

Much of the Arctic Ocean is fairly shallow compared to other oceans. There must have been times in the past during severe ice ages that a lot of what is now the ocean bed was above sea level. When was ...
4
votes
1answer
89 views

Is there a table with decomposition temperatures of common minerals?

I am about to perform a Loss On Ignition test on a material I know that contains among on things kaolinite, which will release water at 500 $^oC$. However, I tried finding a table with decomposition ...
3
votes
2answers
3k views

Are there any areas on Earth with purplish-colored soil/sand/rock/land?

This sort of comes from my related question, but only sort of. Are there any areas on Earth with purplish-colored soil? The purple tint would come from some mineral, perhaps deposited by rivers or ...
3
votes
3answers
2k views

Dissolved minerals

I have a question that I am confused about. If a mineral (say limestone) was added to a groundwater system, say like an aquifer and is completely dissolved in solution, can it ever be a solid again ...
3
votes
1answer
78 views

How can the 'crystal cleavage' of apatite have a four-digit number?

On Wikipedia's page for apatite, the crystal cleavage is listed as [0001] or [0101], which I assume are Miller indices.... But how can there be four numbers/digits instead of two, like there usually ...
3
votes
2answers
591 views

I found this strange spherical stone in Gillette Wyoming. I have no idea what it is. Please help. [closed]

These are recent pictures of it. It’s heavy, I see small minerals that catch the light in it, very bumpy, spherical, doesn’t seem to be magnetic, I was falling down a deep trench and kicked it up at ...
3
votes
1answer
2k views

What's the difference between cleavage and fracture?

I see both terms refereing to fractures on crystals or minerals, so I wonder if they could be considered synonymous. If no, what's the difference between both terms?
3
votes
1answer
329 views

Preservation of clay items

I have a general question which may sound naive: archeologists eg in Ancient Greece take a lot of information from preserved pottery they found. What physical attributes of ceramic items made of clay ...
3
votes
1answer
276 views

Differentiate a rock and mineral

How to differentiate between a rock and a mineral by merely looking at it as a thumb rule?
3
votes
1answer
53 views

What questions to ask to students from a mineral guide dataset?

I am programming an app that consist in 180 mineral sheets of interest for geology students. My database have the following fileds: Identifier Name Name 2 Type Class Formula System Environment1 ...
3
votes
1answer
237 views

Cleavage of minerals

What is the difference between 3-dimensional cleavage and cubic cleavage? I think, they are the same, but I am not sure about if I was right or not.
3
votes
1answer
51 views

Hyperspectral Detection of Ore

How can I use hyperspectral satellite imagery to remotely detect copper or any prespecified mineral deposit in general? Where can I find a database of the absorption and reflection bands of various ...
3
votes
1answer
636 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 ...
3
votes
1answer
80 views

What causes this white coloration of the ground in Gilf-Kebir?

It seems, these white blotches are reflective enough that they caused oversaturation of a spot of image taken from a satellite at the L1 lagrangian point (click to open at max resolution, the purple ...
3
votes
0answers
23 views

Can geochemical anomalies of stream sediment samples be used directly for mapping targets?

We know that geochemical dispersion in stream sediment is much widespread, facilitating discovering mineral targets in a regional scale. However, we also know that there should be discrepancy in space ...
3
votes
0answers
28 views

Looking for videos/GIFs of petrification/permineralization

Do you know of any good animations, videos, or GIFs of petrification/permineralization? For some students verbal and written explanations don’t work, they don't always visualize well. So it’d be ...
3
votes
0answers
146 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 ...