Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [crystallography]

questions relating to the arrangement of atoms in solids, such as the ways in which crystal structure influence material properties, or suitable analytical methods e.g. X-ray diffraction and microscopy

1
vote
2answers
36 views

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....
3
votes
1answer
106 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?
5
votes
1answer
89 views

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 $1.56 \times 10^{-8}$, for an abundance of approximately one part in 630 thousand of the ...
2
votes
1answer
45 views

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?
1
vote
0answers
24 views

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 ...
0
votes
0answers
18 views

How does chalcedony containing quarts and mogánite form?

I just learned that the cryptocrystalline form of silica, chalcedony, usually contains 1-20% of the monoclinic $\ce{SiO_2}$ mineral mogánite as well as the much more common hexagonal quartz. With time ...
2
votes
1answer
130 views

What exactly are enantiotropic and monotropic polymorphic transitions?

Recently, I've been studying the subject of polymorphism and met two important concepts, the monotropic and enantiotropic polymorphic transition types. However, I can't really seem to grasp the ...
4
votes
2answers
76 views

Iron-nickel phase in pallasite meteorites

I have recently been learning and researching about meteorite types and classification. Pallasites are mainly composed of a 'solid-solution' of olivine crystals and an iron-nickel alloy. My question ...
4
votes
1answer
299 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 ...
1
vote
0answers
76 views

What mineral is this green part of stone?

On my trip to Chamonix Alps I found this stone and I'm really interested what is this dark green mineral. Color of the stone is dark green. I can't break a bit of it and it seems very much ...
1
vote
1answer
26 views

How can crystal habit be determined when rock is worn and rounded?

In many cases when I find interesting rocks they are worn and rounded off so the crystalline structure is not clear. How can I determine what kind of crystal it is in those cases? Is there a simple ...
8
votes
3answers
207 views

Is every space group realized by some mineral?

Every mineral has it's own internal building scheme, a lattice on which it's atoms lie. Mathematically, this can be described by the space group of the mineral. From mathematical considerations it's ...
5
votes
2answers
122 views

What are these crystals?

I have got a whole bunch of these crystals.
8
votes
1answer
913 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 ...
-3
votes
1answer
126 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
3
votes
1answer
79 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 ...
8
votes
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 ...
4
votes
1answer
87 views

Reciprocal space in the context of x-ray diffraction and a crystal lattice?

Could someone please explain what reciprocal space means in the context of of x-ray diffraction of a crystal lattice?
2
votes
1answer
82 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 ...
7
votes
1answer
96 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 ...
3
votes
1answer
88 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 ...
4
votes
0answers
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 ...
3
votes
1answer
401 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 ...
13
votes
1answer
213 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 ...
3
votes
0answers
40 views

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 ...
12
votes
1answer
580 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 ...
10
votes
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.
6
votes
2answers
13k 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 ...
17
votes
2answers
12k 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.
44
votes
5answers
11k views

Why do snowflakes form into hexagonal structures?

Snowflakes are known to form into pretty hexagonal structures. The image below shows a variety of such structures that are possible (although by all means not an exhaustive list): What is the ...
15
votes
2answers
13k 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 ...
21
votes
2answers
12k 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 ...