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. L

    Dr. Emoto's : the structural formation of ice crystals

    Hello every one I hope I'm in the right place to ask this question :) well , have you heared about Dr. Emoto's ? http://www.is-masaru-emoto-for-real.com/" my friend were in US last year , and she was joining some one who provides her by these info. when she told me , it was my 1st...
  2. S

    Piezoelectric Crystals: Constant Pressure & Electric Field

    If a constant pressure is kept on a piezoelectric crystal, will it continue to generate an electric field?
  3. L

    Why is the wavelength in a crystal assumed to be the same as outside?

    I read an introductory text about diffraction of X-rays in crystals and I am not sure why the wavelength in the crystal is assumed to be identical to the wavelength outside the crystal. I think that the speed of electromagnetic waves can depend on the type of matter, so wavelenghts can be...
  4. P

    Monocrystals vs. Crystals: Understanding the Difference

    Can I say that monocrystals, polycrystals,crystalline ... are types of crystals? What is the difference between monocrystal and crystal? I don't see any difference in definition?! In statistical mechanics for example if you say crystal you don't mean crystalline. Thanks for your answer
  5. B

    MATLAB Solving Photonic Crystal Resonance Frequency with Matlab

    Hi, I research on photonic crystals.I want to compute resonance frequency for single cylinder scattering. I use the below expression : J'(nkr)H(kr)-J(nkr)H'(kr)=0 J:bessel and H:hankel function. but I can't achieve correct result by write program in Matlab for computing that. Can you help me ?
  6. H

    Chemistry 1 hydrated crystals lab

    Homework Statement "Use your experimental data to calculate the formula for hydrated MgSO4" Homework Equations i used 2.25g x 1 mole/141.46 = 0.016 moles The Attempt at a Solution i'm not sure how to calculate the formula. how do i do that? is there a different equation involved...
  7. T

    Tight binding in cubic crystals

    \phiHi all, I would like to make band structure calculations with tight binding method and I start reading about this method from Ashcroft - Mermin, Chapter 10: The Tight Binding Method and try to solve the problems at the and of the chapter. In problem 2 a. As a consequence of cubic...
  8. A

    Exploring the Formation of Crystals of Inert Gases - Charles Kittel's Insights

    Hello every one :) Actually i was studying from Charles Kittel ( introduction to solid state physics ) about crystals of inert gases , then i asked my self how could inert gases forms a crystals , i couldn't answer that , and no place to read about it :( . So can you people...
  9. A

    Is the tail correction method suitable for all crystal structures?

    Hi all, I'm doing classical (Monte Carlo) simulations on crystal structures using so far the following tail correction where \rho(r) is the pair correlation function and U(r) the pair potential. 2N\pi\rho\int_{r_{c}}^{\infty}\mathrm{d}r\, r^{2}U(r) It is usual to assume that \rho(r)=1 for...
  10. J

    Shock waves in crystals - temperature effect

    If you induce a shock wave in a covalent crystal using an ultrashort laser pulse, is there any way to estimate the temperature rise in relation to the pressure? Say I want to induce pressures of 10's of GPa. Is there a general way to think of this problem? I know next to nothing about shock...
  11. S

    Exploring K-Space & Momentum Space in Crystals

    Hi, I am having trouble understanding some things about k-space or momentum space in a crystal. The trouble began when I was first introduced to the Bloch theorem, a few weeks back. It is: \psi_{n\mathbf{k}}(\mathbf{r})=e^{i\mathbf{k}\cdot\mathbf{r}}u_{n\mathbf{k}}(\mathbf{r}). In...
  12. N

    Solid State: What is a Conventional Cell?

    Hi When talking about crystals, then what is a "conventional cell"? I know what a primitive cell is, but not what a conventional cell is. E.g. see this: http://www.scribd.com/doc/91701/Crystal-Lattices Here they do not describe a conventional cell, but just mention the name.
  13. G

    How do water crystals grow in freezing temperatures?

    https://www.youtube.com/watch?v=_S1ZiNCz6CA In this video, the chief researcher is shown collecting a water sample from a very beautiful location in Japan. He takes it back to the lab, and divides the sample into 50 petri dishes. The amount of water in each petri dish is 1 ml. He then freezes...
  14. D

    Ionic Bonds and ionic Crystals

    is that at equilibrium, energy,U=0 from the equation below? U(R) = −(A /R6 )+ (B/R12 ) i nid to differentiate the equation and equate U=0?
  15. H

    Did I Successfully Obtain Crystals in My Organic Lab Experiment?

    In organic lab this week we were mixing (1-R, 2-S) ephedrine with mandelic acid to get crystals. I dissolved both compounds in 6 mL 95% EtOH and then poured them together. After cooling + glass prodding I should have had no trouble getting crystals. HOWEVER, during the cooling I accidently...
  16. T

    Salt Crystals: Do Negative Ions Emit?

    I'm not sure where this question belongs, maybe in chemistry? move it if necessary. so the quest is this I have a salt crystal lamp. it is a large block of salt on a wood base with a light bulb inside a hollow in the salt. the selling point of these lamps is that the heat from the...
  17. I

    Maximum Drive Voltage for Quartz Crystals: How Much Is Too Much?

    When it comes to the piezoelectric effect you can have a small quartz crystal and apply a force to it and get thousands of volts as a result. But if you took a quartz crystal and applied a thousand volts to it, would it just crack? For a quartz crystal to take a couple thousand volts charge (no...
  18. C

    Properties of 2D Photonic Crystals

    Hello, I'm a business major who has recently stumbled upon the interesting phenomena of photonic crystals. After reading numerous papers and websites on the topic; however, there are many things that go over my head since I have very little knowledge in physics. I'm hoping that someone with...
  19. C

    Why use x-rays to study crystals?

    In order to study the structure of crystals, scientists normally use X-rays. Why do they use X-rays and not visible light? I'm thinking it has something to do with wavelengths, but I do not know why the difference of wavelenght matters.
  20. J

    Physical Chem Question - Xrays & Crystals

    [Xray reflection 1. Homework Statement X-rays of 1.54 angstroms are reflected off copper powder @ 21.65º 25.21º 37.06º 44.96º 47.58º Find the cubic lattice and the length of an edge of the unit cell. 2. Homework Equations nλ = 2d sin(Θ) ; the Bragg equation 3. The...
  21. T

    Circuit designs with crystals and layout of digital clock lines

    I have two different types of questions regarding crystals and clocks. I can't remember if I've asked these question before. I'd appreciate any input on this topic. Crystal external circuitry: Almost any IC with an external crystal has two pins to connect to it. Now my question is how...
  22. wolram

    Unexpected Forms of Liquid Crystals in Ultrashort DNA Found

    http://www.sciencedaily.com/releases/2007/11/071122151148.htm ScienceDaily (Nov. 23, 2007) — A team led by the University of Colorado at Boulder and the University of Milan has discovered some unexpected forms of liquid crystals of ultrashort DNA molecules immersed in water, providing a new...
  23. H

    Geometry Optimization of Crystals

    I'm stuck with a problem of finding the minimum energy of an inorganic crystal. Crystal is of monoclinic structure with 18 parameters to specify its internal coordinates and 2 atomic species. Am using a classical interatomic potential found in literature. The minimization involves both the...
  24. T

    Forehead Thermometer: How Liquid Crystals Work

    Yoy guys, I am working on an invention recently which is related to liquid crystals. I want to know how liquid crystals in a forehead thermometer works. Or basically, how a forehead thermometer works! Thx guys!
  25. N

    Exploring the Effects of Continuous Pressure on Piezoelectric Crystals

    I wanted to ask if a continuous pressure on a piezoelectric produce a continuous potential or not??if not why??
  26. B

    Optical Phonons in Single Atom Crystals: Unraveling the Mystery

    I thought optical phonons only existed in crystals with two or more types of atoms in a unit cell. But I keep reading references of optical phonons in single atom crystals, like silicon. What's the deal here?
  27. S

    Can we use lasers to store and transfer data in crystals?

    First i want to say hello, since i am new here. ok, I don't know tons about physics, so the following is an idea that i have, and would like to know if it was possible. my idea is: Why not use a laser to write 0's and 1's inside a glass or stone crystal? we can already use such lasers...
  28. R

    Electricity generation through crystals

    Hi, You can be sure that the method that I'm going to propose is of no commercial significance. Anyway, I'd like to know why. Set up(regardless of dimensions):- place two permanent magnets with like their like poles closest to each other in a linear tube and at the end of the tube...
  29. A

    Filming Crystals: Capturing Crystal Formations in Liquid

    Not sure if this is right place to be asking-here goes: Am a video art student and am interested in capturing crystals in liquid- Have noticed crystal formation in some semi freezing oil which visually is pretty interesting! Really not knowledgeable in the field of chemistry / physics...
  30. P

    Producing Nickel Crystals: B & D are Correct Answers

    Homework Statement Which two of the following could be used to produce crystals of nickel? A Addition of a piece of copper to a NiSO4 B Addition of a piece of zinc to a NiSO4 solution. C Addition of a piece of potassium to a NiSO4 solution. D Electrolysis of molten NiSO4. Homework Equations...
  31. J

    Refraction of light through ice crystals

    can someone explain to me how sundogs form? I know it has to do with refraction of light through ice crystals but i need a good ray diagram explaining this...
  32. T

    Salt Crystals: Shape & Structure

    What is the shape of salt crystals.??
  33. M

    Miller-Bravais scheme for Hexagonal crystals

    Hello, sorry to bother again but I've been giving this much thought as well and am very confused.. Please refer to the following page: http://x5.freeshare.us/119fs641427.jpg If I am supposed to calculate the direction vector for the hexagonal crystal, I was told to: 1) Calculate the...
  34. S

    Distance between planes in crystals

    I'm working on a lab report on powder X-ray diffraction off of some relatively straight-forward crystals (Si, NaCl, CsCl) for an introductary course on modern physics. I thought it would be useful to include a partial derivation of the formula relating the distance between parallel planes, d...
  35. S

    Exploring the Analogy between Liquid Crystals & Cosmic Strings

    http://arxiv.org/abs/gr-qc/0509091 A liquid crystal analogue of the cosmic string "We consider the propagation of light in a anisotropic medium with a topological line defect in the realm of geometrical optics. It is shown that the effective geometry perceived by light propagating in such...
  36. H

    Melting Point of Inert Gas Crystals: Neon, Argon, Krypton & Xenon

    I am in search of physical properties of inert gas crystals ( such as colour,lustre,etc). I could get only the melting point. Specifically, i want for Neon, Argon, Krypton and Xenon which are fcc.
  37. Astronuc

    Elastic wave modes in crystals

    from C.Z. Tan, Optical interference in overtones and combination bands in \alpha-quartz, Journal of Physics and Chemistry of Solids 64 (2003) 121–125. [1] M. Born, K. Huang, Dynamical Theory of Crystal Lattices, Clarendon Press, Oxford, 1988. [2] C. Kittel, Introduction to Solid State...
  38. D

    Photonic Crystals: Basics & Beyond for Solid State Physics

    Hi, I would like good information about photonic crystals. Does anyone know where to find this? I would like the text to begin at the basic concepts. The only Solid stat physics book i have is "Introduction to solid state physics" 7th Edition by Kittel and it doesn´t say much about this...
  39. C

    Which Book on Gems & Crystals is Best for Beginners?

    I need some help here guys. I'm looking at three books about gems and crystals and I want to see what y'all recommend. The three are the following: Stones Alive! by Trintress, The Crystal Bible by Judy Hall, and Healing Crystals by Cassandra Eason. Keep in mind, guys, that I'm just a beginner...
  40. T

    Shock waves in crystals and frequency changes

    Shock waves propagating in photonic crystals can be used to lower or raise the frequency of light passing through them. It seems (to me) to be some kind of Doppler effect at work here. The electrons in the atoms of the crystal absorb the light, and as they move because of the propagating...
  41. Integral

    Crystals that modify the frequency of light.

    This is an interesting new development.
  42. Tyger

    Testing Magnetic Properties of Iron Crystals without Damage

    Was going to put this up a couple of days ago but was a bit preoccupied. So here goes. Imagine that you take a single crystal of Iron, a whisker, and bend it around to make a circle. How could you find out if the crystal was magnetized? Remember, all the magnetic field is contained inside the...
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