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Questions tagged [mineralogy]

Questions relating to the scientific study and identification of minerals.

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33 votes
3 answers
12k views

Why do felsic materials have lower melting points than mafic?

It is clear from Bowen's reaction series that more felsic minerals have lower melting points than mafic minerals. As far as I know, the same is true of quenched glasses. Felsics have a higher degree ...
foobarbecue's user avatar
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22 votes
3 answers
23k 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 ...
Kultid_Games's user avatar
22 votes
2 answers
4k views

In what geological situations can I find gold?

I've heard that gold ore is often associated with quartz veins. What geological processes enable gold particles to naturally cluster together like this? What characteristics/properties should I look ...
Paul's user avatar
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22 votes
2 answers
3k views

Peak phosphorus - what are the sinks?

The minable phosphorus reserves are limited. Where is the mined phosphoprus landing, what are the global phosphorus sinks? I would assume that most phosphorus is used for fertilizer and ultimately ...
mart's user avatar
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21 votes
2 answers
2k views

Why are minerals found in "large" quantities and not scattered throughout the earth as individual atoms?

Heavier elements are created in stars. After stars die they scatter these heavier elements throughout the universe. These elements eventually gather to form planets. But why do we find "chunks" of ...
Zac Patterson's user avatar
18 votes
5 answers
48k 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 ...
Nirvik Baruah's user avatar
18 votes
3 answers
19k 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.
Azzie Rogers's user avatar
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17 votes
2 answers
21k 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 ...
Kenshin's user avatar
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16 votes
3 answers
31k 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 ...
Ben Hollier's user avatar
15 votes
1 answer
695 views

Why would India have so much thorium on its beaches?

The recent BBC News article Why India Wants to Turn its Beaches into Nuclear Fuel includes the passage: The tropical beaches of India probably bring to mind sun-dappled palms, fiery fish curries and ...
uhoh's user avatar
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14 votes
3 answers
7k 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 ...
Azzie Rogers's user avatar
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14 votes
1 answer
184 views

In what sense did the Oklo reactor "trap" its own nuclear waste?

A number of popular writings on the natural fission reactor at Oklo, Gabon (e.g. here) state that some of the energetic byproducts (krypton and xenon, presumably 85Kr and 133Xe) of the reactor were "...
senshin's user avatar
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13 votes
1 answer
4k views

Can ultrasounds be used to map the density of large underground regions?

This question arose from a related one at Physics.SE, along with my own personal quest to better understand mineralogical prospecting. I want to know if some kind of ultrasound machine can determine ...
DrZ214's user avatar
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13 votes
1 answer
40k views

What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?

There are two groups of elements that are frequently mentioned when discussing incompatible trace elements. They are the high field strength elements (HFS or HFSE) and the large ion lithophile ...
Gimelist's user avatar
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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 ...
Petr Hykš's user avatar
13 votes
1 answer
910 views

Why does halite have perfect cleavage at the (110) plane?

Why doesn't it cleave nicely along the (100) or (010) or any other planes? What determines its cleavage plane? I know it has something to do with the fact that it crystallizes in face centered cubic ...
Tamás's user avatar
  • 515
13 votes
1 answer
338 views

Why does aragonite form in one case and an acetate in another?

If I add acetic acid to limestone, I can get calcium acetate crystals to grow but if I add acetic acid to dolomite, supposedly I can grow aragonite which is a form of calcium carbonate. Why would I ...
Chris Winchell's user avatar
12 votes
1 answer
81 views

Why are titanium oxides lumped in with magnetite for the purposes of analyzing water bubble nucleation?

I was reading a bit about the fluid mechanics of volcanoes to further understand some of the dynamics of "magma wagging" from my earlier question. From [2]: Heterogeneous nucleation, in ...
jonsca's user avatar
  • 1,079
11 votes
1 answer
9k views

How do you use the streckeisen (QAPF) classification ternary diagram to identify igneous rocks based on chemical rock composition?

I have been given the following diagrams: and and a database that is structured like this: ...
Avi Mosseri's user avatar
11 votes
1 answer
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 ...
user avatar
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 ...
Marijn 's user avatar
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10 votes
1 answer
6k 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.
Tamás's user avatar
  • 515
10 votes
1 answer
274 views

Simplest formula of a calcium phosphate mineral?

I had a homework question: Given the formula: $$\ce{Ca}_x\ce{(PO4)}_y\ce{OH}$$ Find the lowest possible values of $x,y$ and state (look up) the mineral name. Based on the anion charges ...
Mecury-197's user avatar
9 votes
2 answers
454 views

How are paleomagnetic polarities determined?

In magnetostratigraphic logs various chrons are distinguished with either normal or reversed polarity, with the magnetic north pole at the geographic north and south pole, respectively. How and why ...
hugovdberg's user avatar
  • 2,672
9 votes
2 answers
1k views

Will the sea get saltier forever?

The sea wasn't always salty. It's been getting saltier over millions of years as minerals dissolve. Is there a natural limit to this process, or the will the sea keep getting saltier forever? Is there ...
spraff's user avatar
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9 votes
1 answer
504 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 ...
DrZ214's user avatar
  • 2,185
9 votes
1 answer
10k views

Is it theoretically possible to artificially create amber?

It is said of amber that it requires thousands of years of time and much pressure to produce amber from tree resin. This was also said of diamond as well, but we now produce artificial diamonds by ...
Cyberherbalist's user avatar
9 votes
1 answer
555 views

How does the composition of volcanic rock change as it makes its ascent towards the surface?

A schematic for the fluid mechanics of a volcano is represented below. Graciously borrowed from Figure 1 of the reference cited below From the caption of that figure: During explosive eruptions, ...
jonsca's user avatar
  • 1,079
9 votes
1 answer
168 views

What makes the conditions at the core/mantle boundary ideal for aluminum to combine with other elements besides oxygen?

Recently, steinhardite was accepted as a new mineral by the International Mineralogical Association. It's quite an interesting story in its own right. There's an interesting article in New Scientist ...
jonsca's user avatar
  • 1,079
8 votes
1 answer
2k views

How are spherulitic structures formed in basalt rock?

After having studied the thin sections of basalt under the microscope, I have come across many spherulitic structures occurring in clusters. How can this happen? Is it due to devitrification or is ...
Prashant Terkar's user avatar
7 votes
3 answers
3k views

The different types of plagioclase

The fractions of albite $\ce{NaAlSi_3O_8}$ and anorthite $\ce{CaAl_2Si_2O_8}$, which I call $\ce{Ab}$ and $\ce{An}$ in the following list, present in a plagioclase are often used to define it in the ...
Self-teaching worker's user avatar
7 votes
2 answers
445 views

What is serpentinization, in the context of disappearance of surface water on Mars?

The recent paper in Nature The divergent fates of primitive hydrospheric water on Earth and Mars (Nature 552, 391–394 (21 December 2017) doi:10.1038/nature25031) has been linked by many recent news ...
uhoh's user avatar
  • 7,072
7 votes
2 answers
2k 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 ...
Sarah Szabo's user avatar
7 votes
1 answer
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 ...
Tyler Durden's user avatar
  • 1,804
7 votes
2 answers
420 views

Acidity of rock

I read that the acidic character, or, better, persilicic character of a rock is determined by a content of more than $65\%\ \ce{SiO_2}$. A rock is defined, by the texts available to me, as ...
Self-teaching worker's user avatar
6 votes
5 answers
382 views

Which Earth minerals would Moon colonists miss the most?

In my science-based novel, Moon colonists need to return to Earth to collect some rare or absent mineral(s) Ideally, something they could derive from seawater. Which minerals might they be...?
Bob Goddard's user avatar
6 votes
1 answer
501 views

Are there probably decent oil fields located in the middle of the ocean?

I did a google image search for a world map of offshore oil. Surprisingly I found virtually nothing. I had to search country by country for such maps. I noticed most if not all were located very near ...
DrZ214's user avatar
  • 2,185
6 votes
1 answer
123 views

Does muscovite occur as a contact metamorphism mineral?

Does muscovite occur as a contact metamorphism mineral, with dacitic intrusion into dacitic rocks?
Muharrem Yavuz's user avatar
6 votes
1 answer
100 views

Why is the Lunar crust anorthite?

The primordial Lunar crust is mostly calcic plagioclase. However, why did the Lunar Magma Ocean produce so much anorthite, why not a feldspar of a different composition, like albite or orthoclase for ...
Andy's user avatar
  • 61
6 votes
1 answer
183 views

If the study of "minerals" is covered by inorganic chemistry

I am wondering what field studies "minerals", such as the minerals in Wikipedia's list. I keep thinking that perhaps it would be covered in inorganic chemistry (list of inorganic compounds wiki), but ...
Lance's user avatar
  • 269
6 votes
3 answers
2k views

What are the dominant elements that oxygen is bonded to on earth?

Elements are found in different minerals and chemical compounds on earth. Oxygen is dominantly found in silicate minerals which, aside from silica, contain other elements. One way of looking at the ...
haresfur's user avatar
  • 4,419
6 votes
2 answers
312 views

Is the association of fluorescent minerals calcite, fluorite, and apatite with fluorescent rare-Earth minerals a coincidence?

If I understand this answer and this comment correctly, minerals like calcite, fluorite, and apatite are "commonly associated with (Rare Earth Element) REE deposits", and like some REEs also fluoresce ...
uhoh's user avatar
  • 7,072
6 votes
2 answers
3k 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?
Kate's user avatar
  • 111
6 votes
2 answers
1k 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 ...
Phillip Allen's user avatar
6 votes
1 answer
155 views

Identifying trichroic crystal systems

An unknown mineral shows three distinct pleochroic colours. Explain what observations you need to make in order to decide which crystal system it belongs to. If it has three pleochroic colours this ...
bon's user avatar
  • 2,211
6 votes
0 answers
99 views

Why does asbestos grow in a hierarchy of separable fibers of separable fibrils; why don't they stick to each other or grow into each other?

Wikipedia's Asbestos begins: Asbestos (/æsˈbɛstɒs, æz-, -təs/) is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, ...
uhoh's user avatar
  • 7,072
6 votes
0 answers
65 views

Formation of Hematite on Mars via Perchlorates as an Oxidizer

Hematite on Mars is generally thought to have formed either in pools of water or from volcanic activity. A comment to the answer to the question: How do hematite and magnetite form? states that ...
Fred's user avatar
  • 24.7k
6 votes
0 answers
74 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 ...
Henry's user avatar
  • 111
6 votes
0 answers
1k views

Could this be pyroxene twinning ? (thin section)

I found this beautiful euhedral pyroxene crystal in thin section today. There is one thing that I can´t explain though. In crossed polarizers, the crystal shows two different interference colors, ...
Petr Hykš's user avatar
5 votes
1 answer
315 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 ...
Durge's user avatar
  • 53