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Questions tagged [crystals]

A solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

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Possibility of naturally cut diamonds

Is there a chance that diamonds may naturally occur as any of the geometric shapes in such a way that it is naturally brilliant and cut? Obviously, I am not expecting really sophisticated cuts but ...
Dr. user44690's user avatar
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What stone/crystal is it? [closed]

I found this stone/crystal when I walked down the street few days ago. I picked it up since it looks very different with other stones in the area, I am really curious about what stone/crystal it is, ...
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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
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5 votes
1 answer
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What is this fossil? What is this crystal?

My daughter found this fossil while walking through the Swabian Jura, in Southern Germany. She asked me about it, but I have absolutely 0 clue about geology. The crystal part is 3cm in diameter, but ...
Eric Duminil's user avatar
6 votes
2 answers
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When diamonds "migrate" from deep underground to the surface, do they maintain pressure inside when there is no more pressure outside? If so, how?

From Science News' A mineral found in a diamond’s flaws contains the source of some of Earth’s heat: A tiny bit of rock trapped inside a diamond is now opening a brand-new window into what the planet’...
uhoh's user avatar
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4 votes
1 answer
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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 ...
Kurt Hikes's user avatar
5 votes
4 answers
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Sources or strategies for stone identification

I have a bunch of semi-precious stones here, but I am not very learned in geology etc and I would like to have some way to know what kind of stones they are. As far as I understand question about ...
Ergative Man's user avatar
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Can crystal lattices be analogue? [closed]

This question might turn out to be more about physics then geology so apologies in advance if that is the case. Years ago I read something that said in crystals "atoms have finite positions along the ...
Tailspin's user avatar
2 votes
1 answer
2k views

Geode-like rock but it's empty inside. Why does this happen?

I found this geode-like rock (spheroidal shaped with empty spheroidal cavity inside) near Dickson Tennessee, USA. Comments suggest that this is in fact geode, but it is empty and featureless inside. ...
Kendra's user avatar
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2 answers
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What does the unit cell of petitjeanite look like?

The question in Chemistry SE What is the crystal structure of bismuth oxyhydroxyphosphate (BOHP)? is about a catalyst synthesized by accident. A link in this comment points to the page https://www....
uhoh's user avatar
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3 votes
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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?
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6 votes
1 answer
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Does Xenon really covalently bond to oxygen within quartz?

Wikipedia's Xenon; occurrence and production says Within the Solar System, the nucleon fraction of xenon is $\small\mathsf{1.56 \times 10^{-8}}$, for an abundance of approximately one part in 630 ...
uhoh's user avatar
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2 votes
1 answer
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An oblique-square-prism crystal?

Does any mineral crystallize in the shape of an oblique square prism? If so, what crystal system (monoclinic, cubic, hexagonal, etc.) would such a mineral fall under?
resplaine's user avatar
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Crystallography: The shape of axial divergent profiles

I don't know if crystallography related topics go into this stack exchange, so sorry if that's wrong here. My question concerns the characteristic shape of axial divergent powder patterns. According ...
Justanotherchemist's user avatar
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1 answer
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I need help with these geode like rocks [closed]

I found these rocks in my pasture and was excited because I thought I had found some geodes. The rocks were in a sandy bank and looked like eggs sticking out of the bank. I am located in Ness County ...
Michelle Tillitson's user avatar
3 votes
1 answer
349 views

What kind of rock or stone is this? Where did it come from? [closed]

I found this on the side of the road in Oregon, i think it was left or forgoten about thats why it was left there but it has crystal pockets, multiple colors, some smooth sides, perfect circles and ...
Olivia Dick's user avatar
1 vote
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Electric permittivity of quartz

I'm performing an educational experiment on the piezoelectric effect in quartz, and it would be useful for me to know its electric permittivity. I've been told that the quartz sample that I have is ...
sbs95's user avatar
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2 answers
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What type of yellow-green stone is this? [closed]

It's greenish yellow with white. Got it in a mixed stone package from Amazon. No luster, I'd say a 7 in hardness, it doesn't look homogeneous.
Cheyenne's user avatar
1 vote
1 answer
258 views

is this a rose quartz

pink quartz looking stone 19 pounds found in a vehicle in new york state
m0mmy1225's user avatar
4 votes
1 answer
904 views

Applications of differential/integral calculus in crystallography (teaching undergraduates)?

I'm a mathematics professor who is seeking to find interesting, application-driven ways of teaching freshmen college students differential/integral calculus. I am in no way versed in crystallography ...
Sinister Cutlass's user avatar
4 votes
1 answer
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Can the formation of gypsum evaporites (sand roses) be simulated in the lab?

Has the process of formation of sand roses been simulated in laboratory conditions, or does it take too long?
HannesH's user avatar
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3 votes
2 answers
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A few questions about glass

A glass, as I understand it, is a material whose solid phase is amorphous and which undergoes a glass transition when heated. My train of thought - and therefore my questions - began with obsidian. ...
MT_Head's user avatar
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1 answer
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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 ...
user6253's user avatar
0 votes
1 answer
2k views

Why there are no sharp corners in nature?

I have read some articles explaining why rounded corners are more aesthetically pleasing, like this one and it all makes perfect sense but my question is: Why does nature not have sharp corners? What ...
ruslaniv's user avatar
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18 votes
2 answers
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Is this ice cover real - and what circumstances are required to make it?

The title says it all... I assume it requires very slow freezing sheltered from the wind. Undercooled water, maybe? A Reddit thread talks about Delaunay triangulation, but that does not explain how ...
Jan Doggen's user avatar
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4 votes
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What is the name for a ABC hcp lattice that is squeezed along the direction vertical to the ABC planes?

I am trying to classify a bravais lattice. It is a hexagonaly close packed lattice with (ABC) planes, that is fcc, but it is squeezed along the stacking direction, so perpendicular to the planes. Just ...
Dominik's user avatar
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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
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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
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7 votes
2 answers
19k views

Why are there no crystals with 5-fold symmetry?

They say you can't pack objects like pentagons or octagons such that they fill up space entirely and that that's one reason there is no 5-fold or 8-fold rotational axis. Are you telling me you can ...
Tamás's user avatar
  • 515
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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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
  • 2,842
23 votes
2 answers
21k views

Why do crystals, like quartz and diamonds, form in different colors?

Some crystals, like quartz and diamonds, form in a variety of different colors. For example, quartz can be clear, 'foggy', pink, yellow, and even blue. What happens during the crystal's formation to ...
Azzie Rogers's user avatar
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