Questions tagged [mineralogy]

questions relating to the scientific study and identification of minerals.

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31
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3answers
7k 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 ...
22
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2answers
1k 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 ...
20
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2answers
2k 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 ...
18
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1answer
2k views

What are these metallic nodules that were found at low tide on the UK south coast?

Smooth spherical crystalline metal nodules Outside and inside surface does not scratch with a knife blade Inside lustre brassy, radially striated metallic crystals radiating from a lumpy centre at the ...
17
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2answers
676 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 ...
17
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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
15k 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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1answer
118 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 "...
13
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1answer
3k 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 ...
13
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3answers
4k 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 ...
13
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1answer
25k 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 ...
13
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1answer
221 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 ...
12
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5answers
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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 ...
12
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1answer
70 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 which the ...
12
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1answer
593 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 ...
11
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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
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1answer
121 views

Why would India have so much thorium on it's beaches?

The recent BBC News article Why India Wants to Turn it's Beaches into Nuclear Fuel includes the passage: The tropical beaches of India probably bring to mind sun-dappled palms, fiery fish curries ...
10
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1answer
7k 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: ...
10
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1answer
3k 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
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2answers
325 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 ...
9
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1answer
253 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 ...
9
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1answer
343 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, ...
9
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1answer
142 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 ...
9
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1answer
251 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 ...
8
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4answers
3k 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 ...
8
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2answers
2k views

What is this blue rock?

I am trying to identify a rock my husband found.The rock was found in Columbus Ohio about 20 feet (6 m) down. It is about the size of a basketball and extremely heavy (90 lbs) and difficult to cut ...
8
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1answer
864 views

Rock ID: shiny, very hard, black rock from Louisiana, USA

I have had this for over 20 years and I still don't know what it is. I found it on top of the ground by my dad's workshop in our yard in Louisiana. I don't know how it got there. It weighs 6 pounds 7 ...
8
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1answer
1k 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 ...
8
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2answers
608 views

Identification of dark red, metallic mineral

I recently found this mineral crystallised within quartz at a rock crushing plant. Because of this I have no idea where this rock came from as material is transported to the site from a variety of ...
8
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1answer
3k 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 ...
8
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2answers
668 views

Rock ID: Large, heterogeneous, magnetic rock in Cascade Range, Washington, USA

I found this rock in a glacial till in north central Washington State, on the east side of the Cascade Range. The dark round crystals are roughly 1 inch (2.54 cm) by 2 inch (5.08 cm) in size. The ...
7
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3answers
2k 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 ...
7
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2answers
726 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 ...
7
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2answers
332 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 ...
7
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1answer
357 views

Mineral Rock Identification

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 ...
7
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1answer
1k 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 ...
6
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5answers
181 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...?
6
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1answer
207 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 ...
6
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1answer
576 views

What are the blue spots in this rock?

The rock is 4 inches (~10 cm) long. The vendor claims this rock is from K2. Are the blue spots real or painted on?
6
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1answer
101 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 ...
6
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3answers
653 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 ...
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?
6
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1answer
99 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 ...
5
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1answer
318 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
155 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
279 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 ...
5
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2answers
2k 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
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2answers
175 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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1answer
308 views

What kind of light blue stone is this?

My son found this stone on the beach on the island Crete. It was a one of its kind, no other visible stone on the beach was the same. We asked the locals, but they did not know this stone. It's about ...
5
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1answer
188 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 ...