Questions tagged [mineralogy]

questions relating to the scientific study and identification of minerals.

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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 ...
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45 views

What processes cause basalt to form a columnar structure? [duplicate]

I have run across many pictures of rocks that look like almost perfectly carved columns. For example: the Twyfelfontein Organ Pipes, the Basaltic Prisms of Santa Maria Regla, and the waterfall ...
3
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2answers
128 views

Why do buoyantly rising mantle minerals melt, yet buoyantly rising atmospheric waters condense?

In the mantle, minerals contained in buoyant plumes of rock undergo phase changes from solid to liquid (decompression melting). In the atmosphere, waters contained in buoyant plumes of air undergo ...
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3answers
401 views

Why are there craters on the moon?

The Earth's moon is in synchronous rotation around Earth. The question: Why are there craters on the lit side of the moon and the dark and of which are not parallel with crater schemes on Earth?
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1answer
617 views

How gold deposits can be formed in Himalayas?

I have heard that gold is found in the water coming out of glaciers in Skardu region of Pakistan. Given that this area is part of Himalaya, what processes could result into ores of gold in this area?...
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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 ...
3
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1answer
385 views

Identification of mineral

I recently visited a quarry site and brought home a rock sample that had two clusters of cubic crystals on its surface. I am unsure what the mineral is, I think it may be fluorite but I am not certain....
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1answer
139 views

To find hardness in Mohrs scale [closed]

Except diamondת which mineral is having high hardness in Mohr scale. A Oxide B silicate C carbonate D phosphate
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1answer
81 views

How can a crystal habit be round?

I am confused how hematite can have a "botryoidal" habit when its crystal structure is trigonal, which is an angled structure. How can an angled crystal present itself as rounded? If a botryoidal ...
4
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558 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, ...
4
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2answers
260 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 ? ...
2
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1answer
151 views

Is there any mineral identification techniques that works for all minerals?

Are there any Mineral Identification Techniques that work for all minerals(Non-Metallic/Metallic), so that an electronic device could be made to distinguish between all minerals?
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392 views

I have found this structure in thin section. What is it?

I have been observing a nepheline specimen under polarized light and found some interesting places. I have taken several images. The first shows a micro-geode with parallel polarizers, second with ...
5
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2answers
174 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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216 views

What is solidus and liquidus temperature of granite?

My understanding is that because a rock is composed of variety of minerals, so it does not have fix melting point, rather there is a range below which whole rock is solid and above which whole rock is ...
8
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4answers
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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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1answer
494 views

Help…would like to find out what kind of rock this is. [closed]

Not too sure what kind of rock this is, very interesting looking. Anyone have an ideas. Was found north of the badlands, South of Rapid City.
2
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1answer
62 views

Did we find cinnabarit?

We searched for cinnabarit in an abandoned mine (Google Maps, in Békásmegyer, Hungary). We collected these samples, but as we are not geologists, we are not sure what we found. Pictures about the ...
2
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1answer
163 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
42 views

Is there any covalent crystals that can be easily synthesized?

I am looking for a kind of crystal that can be artificially made at relatively low temperatures (below 1500 degree Celsius) and relatively quickly (not geological time). The product is ideally ...
2
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1answer
83 views

Voronoi-like pattern in metal samples

What is this pattern in the samples' surface called and how/why is it formed? I remember having seen a similar pattern in galvanized sheets. Photos of metal samples from Wikimedia Commons (here and ...
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1answer
240 views

Why do manganese nodules have different constitution than sea water?

Analysing the constituents of manganese nodules, we find that the relative proportion of minerals differs from that of the surrounding sea water. Can someone explain to me why the proportion of the ...
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1answer
656 views

What is the difference between mineral groups and series?

It seems to me when reading about minerals, groups and series are spoken about interchangably in similar types of contexts. Is there a difference? If so, what?
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 ...
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1answer
591 views

Is porphyritic texture always indicative of a 2 stage cooling process?

Is porphyritic texture always indicative of a 2 stage cooling process? Can't the phenocrysts and groundmass be formed at the same time depending upon the chemical constituents forming the rock? The ...
4
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2answers
397 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 ...
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0answers
85 views

Is it ok to use biology microscope for gemological purpose?

Is it ok to use biology microscope for gemological purpose? What's the difference?
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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 ...
6
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3answers
650 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 ...
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3answers
154 views

Connection between microbes and serpentinite?

Serpentinite belongs to the serpentine group. This group of minerals are metamorphic minerals caused a special process called serpentinization. Serpentinization created serpentinite on the Earth's ...
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1answer
70 views

What type of mineral is this? [closed]

My grandfather found this thing.
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1answer
856 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 ...
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3answers
739 views

What kind of rock or mineral is this?

I found this rock or mineral in our backyard, and I'm having a hard time trying to figure it out. Does anyone know exactly what this thing is
3
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1answer
89 views

How do cations control the crystal structure of silicate minerals?

Beyond the obvious fact that in many of the silicate subtypes they play an ionic 'glue' like role by bonding the tetrahedra units together; how do cations control the structure of a silicate and how ...
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28 views

Can humidity changes induce stacking-sequence changes?

My understanding is that some minerals with layered crystal structures will reversibly absorb water with changes in humidity. Are there any minerals where this reversible absorption leads to a ...
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2answers
666 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 ...
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 ...
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2answers
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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 ...
3
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1answer
409 views

Significance of crystal classes in crystallography

I am studying crystals and I learned that there are 32 crystal classes with well-described data regarding symmetries. I have visited a few sites and am having difficulty determining the significance ...
4
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1answer
138 views

Online resources for geographical distribution of minerals

I'm trying to find the geographical distribution and availability of mineral Brannerite. Is there a resource online to know or query where a certain mineral is found? On the link page, they mention ...
4
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1answer
205 views

What type of gem is this?

I was wondering what type of stone this is. I tested it on Mohs hardness scale. It scratched quartz. I found it at Crystal Cave in Kutztown, Pennsylvania. They were selling bags of gems you could sift ...
4
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1answer
1k 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 ...
5
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1answer
447 views

Icelandic rock I am trying to identify

This is a rock that I picked up from underneath a melted segment of Glacier in east Iceland. It is not unusually heavy or light for it's size. I can scratch the surface away with a penny. The ...
13
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1answer
220 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 ...
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1answer
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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 ...
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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 ...
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2answers
331 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 ...
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 ...
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648 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 ...
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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: ...