Questions tagged [minerals]

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17
votes
2answers
13k 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.
15
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2answers
16k 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
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3answers
26k 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 ...
13
votes
3answers
5k 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
5answers
20k 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 ...
11
votes
2answers
1k 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
1k 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
4k 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
275 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
379 views

Mineral Rock Identification [closed]

Went out hiking after some heavy rains and came across an area that looked like broken glass sticking out from mud. On a closer look this is what we found. Not sure what it is and would like to know ...
6
votes
1answer
822 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
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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
173 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
2answers
313 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
1answer
506 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
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
1answer
127 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
2answers
174 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 ...
5
votes
2answers
173 views

Rock Identification: clear, hues of yellow/orange. Washington State [closed]

I purchased this rock at an estate sale along with some rose quartz. The sellers had no information on it. My husband was able to break it today with a hammer, but I have no idea what the material is. ...
5
votes
1answer
214 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
622 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
334 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
90 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
1answer
78 views

Unidentified mineral found in France [closed]

(I am not a native english speaker, so I'm not really aware of the specific terminology.) A few years back, I found an unidentified rock on a beach in Normandie (France). It looks and feels (texture-...
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
2k 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
94 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
58 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 ...
4
votes
1answer
147 views

Can anyone identify this stone? [closed]

I found this rock at the weekend in the forest of Haigh Hall, Standish. It seems to be a solid mass of fibrous material. I have given it a scrub with warm water and a toothbrush just to get rid of ...
3
votes
2answers
2k 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
1k 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
2answers
337 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
89 views

What is this rock I found being sold in a store? [closed]

I was recently on vacation in Hawaii and while there, entered a rock and mineral type store where I saw the rock below. I forgot to ask what it was while I was there and I am unable to go back and do ...
3
votes
1answer
966 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
158 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
2answers
101 views

I don't know what this rock is [closed]

I got this rock a year ago at a mineral and fossil event, and there was a stand where they where selling 'mystery packages', boxes full of different fossils and minerals. I bought one, and figured out ...
3
votes
2answers
80 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 ...
3
votes
1answer
275 views

Mineral identification; black & metallic [closed]

During a recent trip to the Portuguese island of Madeira, I found a couple of interesting rocks on a beach. Both the rocks pictured in this question contain the same black mineral. I first guessed ...
3
votes
1answer
187 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
2answers
151 views

Pinkish quartz like. Help identifying and if it is worth anything? [closed]

I recently purchased a home, in the fireplace surround that I tore down were several rocks (quartz) that I thought were unique. I am looking for identification help and if they were worth anything. ...
3
votes
1answer
44 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
331 views

heavy, brown, rock with crystals, please help identify [closed]

please help identify this rock. it is heavier than most. dark brown color. picture is shown with streak test. found in Philadelphia pa. at home demolition site. crystals seem to be different type and ...
3
votes
1answer
523 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
76 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
129 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 ...
2
votes
2answers
1k views

Melting point of minerals

Looking at this website, I can see the melting point of the following minerals: http://hyperphysics.phy-astr.gsu.edu/hbase/Geophys/meltrock.html Apparently at a temperature of 1200 °C, all the ...
2
votes
1answer
325 views

Deadly minerals

I would like to go into mineral excavation as a hobby. What deters me is the fact there are quite a few deadly minerals/ores out there. My question is how likely is it there are those deadly ores in ...
2
votes
2answers
141 views

How to genetically classify a mineral resulted from weathering?

I am writing a mineral guide for smartphones which classifies minerals according to their formation environment. From sugestions on this related question, I changed the classification to: ...
2
votes
2answers
123 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 ...