What is Crystals: Definition and 142 Discussions

A crystal or crystalline solid is 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. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations. The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification.
The word crystal derives from the Ancient Greek word κρύσταλλος (krustallos), meaning both "ice" and "rock crystal", from κρύος (kruos), "icy cold, frost".Examples of large crystals include snowflakes, diamonds, and table salt. Most inorganic solids are not crystals but polycrystals, i.e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, rocks, ceramics, and ice. A third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever. Examples of amorphous solids include glass, wax, and many plastics.
Despite the name, lead crystal, crystal glass, and related products are not crystals, but rather types of glass, i.e. amorphous solids.
Crystals are often used in pseudoscientific practices such as crystal therapy, and, along with gemstones, are sometimes associated with spellwork in Wiccan beliefs and related religious movements.

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  1. fluidistic

    A Neumann's principle (group theory applied to crystals), Seebeck tensor

    I am reading about symmetries in crystals, and my knowledge in the field of group theory is almost nill. I am reading that, in the worst case, the electrical and thermal conductivity tensors can possess, at maximum, 6 different entries rather than 9, thanks to Neumann's principle which states...
  2. D

    Effect of HCl on NaCl crystallization rate

    I came across a book that said if you add HCl (acid) to a saturated NaCl solution, then the crystallization process of that salt will be accelerated. Is this true, and if so, how? Edit: As it is with these things, I find the solution immediately after making this post. Here is a youtube video:
  3. E

    To derive the piezoelectric effect in crystals

    For a nice cubic non-centrosymmetric crystal like quartz/##\mathrm{SiO_2}## we can imagine that on application of stress the tetrahedral coordination polyhedra become distorted, and the central ion is displaced by a fraction ##\lambda## of the cell parameter ##a##. The total polarisation...
  4. P

    Rotating birefringent calcite crystals: precession of image?

    I have been doing some reading about birefringence in order to understand colors observed in different birefringent crystals when I came across the following page in connection with calcite crystal birefringence. https://www.microscopyu.com/tutorials/birefringence-in-calcite-crystals I think I...
  5. Vanilla Gorilla

    B Time Crystals & Spin: Engineering a New Reality?

    In 2016, https://en.wikipedia.org/w/index.php?title=Norman_Yao&action=edit&redlink=1 et al. proposed a different way to create discrete time crystals in spin systems. From there, Christopher Monroe and Mikhail Lukin independently confirmed this in their labs. Both experiments were published in...
  6. H

    I Understanding Time Crystals: A Beginner's Guide

    Just read an article about time crystals. I understand regular crystals vary in a routine fashion through space but are unchanged over time. Time crystals apparently change periodically over time. I tried the usual googling but my brain has nowhere to put this. Can someone dumb this down for me?
  7. S

    I Why are crystals more conductive then amorphous structures?

    Hey guys basically why are copper crystals more conductive then the corresponding amorphous structure? I know generally that electrical conductivity is reliant on: σ = (e2 * (vf)2 n τ)/3 My attempt of understanding is that the crystal structures are made up of unit cells which implies every...
  8. Quark Effect

    I Explaining Time Crystals: Matter, Mass & 4D

    Can someone simply explain to me what are the time crystals? What are they built from (matter, do they have mass)? I cannot find a clear explanation of them. I just know that ordinary crystals are 3d, time crystals - 4d.
  9. SchroedingersLion

    A Exploring the Discreteness of Allowed k Vectors in Crystals

    Greetings, I am having troubles with understanding the allowed k vectors in a crystal. Bloch's theorem gives us discrete energy bands for each wave vector k. However, only discrete k vectors are allowed. Using periodic boundary conditions, the discreteness is easy to show. But I am having a...
  10. S

    How can I successfully grow high-quality KDP crystals?

    I've been trying to grow a KDP (potassium dihydrogen phosphate) crystal, but I'm having trouble growing anything. I've been adding potassium phosphate fertilizer to distilled water in a bottle I cleaned out and heating it to dissolve the chemicals, but so far haven't gotten much results. It's...
  11. A

    I Taylor Series for Potential in Crystals

    Hi, I've been reading the passage attached below and from what I understand we are looking at a 1D chain of atoms and if anyone atom moves it changes the potential for surrounding atoms and cause a change in energy in the system so the total energy is dependent on all the positions of the atoms...
  12. Edge5

    I Opal Crystals on Mars: Implications for Geochemical Conditions

    People found silica opals exist on the planet Mars, what does this imply about geochemical conditions on Mars?
  13. J

    Experimental procedure for growing piezoelectric crystals

    At school I and a handful of other kids are devising an experiment to send up to ISS to test it over a period of 30 days next year. (Yep, we're quite fortunate to have this opportunity!) We've chosen to grow piezoelectric crystals using (super)saturated solution of the piezoelectric crystal...
  14. J

    Growing piezoelectric crystals experiment

    Homework Statement I'm not sure if this is a forum for these kinds of things. But anyways, at school I and a handful of other kids are devising an experiment to send up to ISS to test it over a period of 30 days next year. (Yep, we're quite fortunate to have this opportunity!) We've chosen to...
  15. J

    Making perovskite solar cell crystals w/o heating

    I'm a high schooler involved in a research in which we aim to grow perovskite crystals in microgravity. I've recently come across this article (https://scitechdaily.com/researchers-develop-a-better-method-for-making-perovskite-solar-cells/) in which they explain how to grow better perovskite...
  16. S

    I Allowed infrared absorption in simple London crystals

    Which infrared photons can London force bound liquids and crystals of simple particles (atoms, and homonuclear diatomic molecules) legally absorb? For comparison: diamond is bound by strong covalent bonds. The restoring forces permit vibrations about the C-C bonds at about 1000/cm. But since a...
  17. John Lutz

    Exploring Crystal Defect Propagation: The Future of Light-Based Computers?

    I'm a coder by trade. Been coding since 1991 professionally. I have always followed science but recently got very interested in crystals after watching the original Superman. I firmly believe that the future of light based computers will by crystal and storage for both of what we consider RAM...
  18. John Lutz

    Regarding Home Lab made to study crystallography

    1) Is it possible to create crystals at home beyond child crystal kits one can buy? I'm very serious about putting work into studying and growing crystals. If so, what do I need? 2) Also how would it be possible to introduce vacancies in crystal growth ? I have heard of things like ionic...
  19. amjad-sh

    A What is inversion symmetry in solids and why does it break at the surface?

    Hello Can somebody explain for me what is the meaning of inversion symmetry in solids? and why does it breaks at the surface? and also why this inversion symmetry breaking leads to SOC(spin orbit coupling)? If somebody also know a document that explain this in full details(from A to Z) please...
  20. Jay Macarus

    I Calculate the distance between two cleaved crystals

    Hey guys, can't seem to make sense of this question from phys. It goes.. "A crystalline solid consists of atoms stacked up in a repeating lattice structure. Consider a crystal as shown in Figure a. The atoms reside at the corners of cubes of side L = 0.200 nm. One piece of evidence for the...
  21. S

    Liquid crystals: dielectric torque and electric torque

    Dear Members, I was reading a tutorial on ferroelectricity of liquid crystals, underneath is the excrept: "For ferroelectric materials, in addition to the dielectric torque, the electric torque will have a term due to the linear coupling between the spontaneous polarization" Could someone...
  22. C

    Laser Crystals -- effects of crystal size

    Say that I have a neodymium doped yttrium aluminum Garnet (Nd:YAG) laser crystal rod. If I'm using this crystal in a laser, will the size of the crystal affect any characteristics of the laser itself. That is, will a laser containing a 4-by-7 mm Nd:YAG rod operate differently than a laser...
  23. N

    Transistors: Tiny Silicon Crystals, Memory Cells, & Shrinking Bits

    Transistors are tiny crystal of silicon. Transistor switch and it's support component are memory cell. A single memory chip can hold up to 4 transistor ? What is the shrinking bit ? Can you please explain?
  24. nomadreid

    I Is the Indicatrix a Volume Chart or an Ellipsoid for Crystal Optical Properties?

    Trying to work through a paper which includes a discussion of the optical properties of crystal, and the author uses the term "indicatrix", at one point referring to it as a diagram, which makes sense, but another place referring to it as a "volume chart", which I haven't figured out. Could...
  25. S

    Why is it that cocaine crystals aren't transparent

    So I admittedly was a former cocaine user. I've since cleaned up and am back in school and my life is going in the right direction for once. I took a class in organic chemistry this previous semester and we did a lab on recrystallization. I think it was boric acid that I recrystallized, but I...
  26. physics_hp

    Photonic crystals as metamaterials

    Why do some photonic crystals show metamaterial property?
  27. Willfrid Somogyi

    I Highest Order Diffraction Ring

    So we have the standard diffraction equation for crystals, being: nλ = 2dsinθ. If we keep the wavelength and the lattice parameter the same then n simply depends on θ. So there must be a maximum order diffraction ring that you could obtain as once you get to 90° you're essentially going in the...
  28. C

    A Free energy density in liquid crystals

    Hi, For someone who's familiar with LC's: How to derive the expression for free energy density of an hybrid aligned LC cell? what should be the vector for the director? I already familiar with the cases of splay and bend cell but couldn't understand how to derive it to the case where the cell is...
  29. K

    Laser frequency doubling range for nonlinear crystals

    This is actually a straightforward question, but I'm struggling to find answers because I don't know very much about lasers. I want to use a nonlinear crystal for frequency doubling in an infrared laser (1480 nm) so that the output is half @ 740 nm. I know that nonlinear crystals like KTP are...
  30. S

    Can a Piezo Crystal be Used as a Segmented Actuator for Voltage Measurements?

    I think I understand the basics of piezo crystals. You apply pressure and the crystal produces a voltage. Conversely, you apply a voltage across the crystal and it deforms. My question is this: if you were to apply pressure to only a small region of the crystal (if that's possible?), would...
  31. sciencejournalist00

    B How do scientists work with nonlinear crystals

    When I point a 5 milliwatts red laser at a pile of barium borate crystals, all I get is red speckles of scattered light. When I point a 100 milliwats blue laser at the same pile of barium borate crystals, I get blue speckles. When I point a 2000 milliwats green laser at the pile of barium borate...
  32. A

    Calculating particle velocity along crystal direction

    I am currently looking at setting up a particle, with energy 5keV, traveling along the [11bar2 0] direction in Zr but I am struggling to get my head around how to resolve the velocity into the 3 directions to make sure it travels along this specific crystal direction. Could anyone help point...
  33. U

    About Crystals in microcontroller......

    I have a question that if we use external quartz crystal in Microcontroller and connect it to battery... Crystal gives regular and very accurate electrical frequency... But it should get mechanical vibration from somewhere to give electrical pulses... From where it receives mechanical vibrations?
  34. Mike Dacre

    Mixed Melting Point of Two Pure Solid Crystals

    I understand why an impure solid will have a decreased melting point, however, in my recent organic chemistry lab section I mixed two finely ground pure solids together and observed that the mixture melted at a lower temperature than either pure solid. I understand this in principle, but...
  35. kelvin490

    X-Ray Diffraction in Crystals: Exploring Scattering & Interference

    In explaining x-ray diffraction of crystals, usually the approach is to consider the atoms absorb radiation and scatter it, at some angles constructive interference occur and bright spots can be observed. It seems that it is different from the diffraction of slits or gratings because in these...
  36. ryanuser

    Piezo crystals and current generation

    hey can a piezo crystal generate current when it is hit as well as when it is exposed to sound?
  37. T

    How Does Adding Sulfuric Acid Prevent Hydrolysis in CuSO4 Crystal Preparation?

    We did this experiment in the lab.We had to prepare crystals of pure copper sulfate from a given impure sample of blue vitriol(powder). So my teacher started with shaking the sample with water and then added a few drops of dilute sulfuric acid to it. It was then heated to crystallization point...
  38. Hamza Abbasi

    Maximizing Current Output in Piezo Electric Footpaths

    Piezo Electric Foot Paths (I am having a problem )? I am building a Piezo electric footpath which will generate electricity , converting mechanical energy into electrical energy . Before building the actual model I have build a test model. The model is generating fairly high amount of voltages...
  39. gracy

    Crystals of high ionic charge are less soluble. why?

    Crystals of high ionic charge are less soluble. why?As we know,when hydration energy is less than lattice energy the ions are not soluble. So,crystals of high ionic charges have less hydration energy right?And it does make sense to me as higher the charge ,greater the lattice energy because...
  40. T

    Do ionic crystals have total electric dipole moment?

    I have come up with a paradox: Ionic crystals, in which cations and anions form a lattice, seems to have total electric dipole moment! For example, consider a one dimensional example: ##+ - + - + - ... + - + -## In the above picture, a ##+## represents a cation and a ##-## represents an anion...
  41. M

    I am trying to find materials to make a pulse laser for lab

    Hello everyone, I am working with my modern physics professor Dr. Parshar to make a pulse laser for my modern physics lab. I have to make an itemized expense report for the materials and all that. I need help figuring out what crystal or doped glass would be best to use, not super expensive...
  42. R

    Determine the intensities of GaAs crystal planes

    GaAs crystal structures have basis atoms: Ga: (0 0 0), (0.5 0.5 0),(0.5 0 0.5),(0 0.5 0.5) As: (0.25 0.25 0.25),(0.75 0.75 0.25),(0.75 0.25 0.75),(0.25 0.75 0.75) i'm trying to find intensities at all of its plane, using this equation: I = (F^2)*m*Lf (m= multiplicity, Lf=lorentz factor)...
  43. R

    Calculation of Intensity of of AX crystals

    I'm still confuse on using the equation about atomic scattering factor, f = a*e^(-b+((sin(theta)/lamda)^2) + c (general equation), where sin(theta)/lamda = 1/2d = 1/(2*(sqrt(a^2/(h^2 + k^2 +l^2)))), so this term is dependent on the plane. which you will used to find the Intensity of crystals...
  44. Sampad Saha

    What is the meaning of the term "Interlocking of crystals "?

    Please note that I'm asking about interlocking OF crystals not "interlocking crystals "
  45. T

    What distinguishes the 32 crystallographic point groups?

    Hello, some weeks ago I was having a first look at the world of crystals: http://en.wikipedia.org/wiki/Crystal_system Now I forgot the bit that I've understood but before trying to study the topic again I would like to ask an other simple question: " What makes the 32 crystallographic point...
  46. vtahmoorian

    Phenomena near the band edge of photonic crystals

    Hi everyone:) Is there anyone who has worked on the phenomena near the band edge of photonic crystals? for example spontaneous emission near the band edge? there are lots of articles specially from Sajeev John " spontaneous emission near the edge of a photonic band gap" Phys.Rev.A vol50 num 2...
  47. S

    Quick question about liquid crystals

    After some reading, I noticed that everybody likes to mention the order parameter and most of the literature simply adds a graph, for example: http://www.personal.kent.edu/~bisenyuk/liquidcrystals/maintypes2.html However, many (all of them, to be exact) seem to avoid the exact expression of...
  48. J

    Testing the piezoelectric properties of Quartz Crystals

    Hello :) I am Jon and I am conducting an experiment with Quartz Crystals to test their piezoelectric properties. I wanted to ask you a question about my experiment set up. Which type of force is required to be applied for voltage to be produced? Could I apply a compressive force with...
  49. J

    Recrystallizing but not getting any crystals

    I am trying to recrystallizing lidocaine out of methanol. I created a saturated solution of lidocaine and hot methanol, waited for it to cool to room temperature, then threw it in a cool water bath. There was no recrystallization. I decided to evaporate the methanol to recover my lidocaine and...
  50. C

    Bloch state + Photonic crystals master equation

    Hello all! I've been trying to go from the second to the third equation shown in the image. Here, \vec{H}(\vec{r})=e^{i\vec{k}\cdot\vec{r}}\vec{u}_\vec{k}(\vec{r}) is the Bloch state for some periodic dielectric arrangement. I have tried using the identity that...