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. N

    Coordination no. in crystals (conceptual)

    what does coordination no in crystal structures really mean? i know it's no of nearest neighbors but has it significantly to do with bonding of electrons. actually my doubt is that - I read Be can't show coordination no of 6 and is allowed to show only coordination no 4 due to lack of...
  2. S

    Research in Photonic Crystals worth it?

    Hi I am doing my Masters by research in Photonic Crystals and I want to do a PhD later as I dream of an academic. I wanted to know to if the field of photonic crystals offers opportunities for growth in the future. Will this field be actively researched in the future? Thanks
  3. E

    Strength In Single Crystals

    Hey, this was the question could someone please help? "An aluminium single crystal alloy aircraft component is oriented such that a tensile stress is applied along a [102] direction. If slip in this material occurs on a (111) plane and in a [101] direction, compute the yield stress at which...
  4. S

    Begineers' books on Photonic Stuctures/ Crystals

    Hi Can you recommend me a simple to begin with book on Photoinc Crystals. I did my undergrad in Electronics Engineering and don't have any knowledge of photonics. Thanks
  5. A

    Atom Energy in Crystals: Gibbs Free Energy

    Does atom at the surface of a crystal have more or less energy than those in the bulk? And how does this relate to their Gibbs free energy?
  6. A

    Unlocking the Potential of Photonic Crystals: Exploring Phonon Transport in 2014

    I wish you a happy new year 2014 full of discoveries, surprises, changes, laughter, smiles, giggles and tenderness Is if possible to Study the phonon transport in photonic crystals.
  7. Z

    Why can photonic crystals be used to create a super lens?

    Firstly, sorry if this doesn't go here please feel free to move it as I was a little confused where to put it. TL:DR Doing a project question interests me, "Why can photonic crystals be used to create a super lens?" Okay so I am doing an undergraduate project for my honours year that I...
  8. A

    Missing Reflections in FCC/BCC Crystals: Bragg Model Inadequate?

    I noticed that using the Laue equations reflections from some of the planes in the fcc and bcc crystal are not allowed. Now using the (maybe too naive?) Bragg model we can always find Bragg peaks whichever plane we hit with waves. So is the Bragg model too simple for these planes? And what is it...
  9. A

    Exploring Waves in Crystals: Acoustical & Optical Branches

    My book considers waves in crystals. Especially it develops the idea of acoustical and optical branches of the waves. From what I can see these are different ways the dispersion of our phonon may look like. It is developed when the crystal contains more than one atom per unit cell, but I am not...
  10. C

    Barium Borate- beta BBO crystals (what am I looking at?)

    The chemical formula, BaB2O4, doesn't correspond with the image I see. Barium is green, boron is pink and oxygen is red. Wiki Barium borate No clue about crystals but willing to learn the basics.
  11. H

    Phonons in Crystals: Standing or Traveling Waves?

    Are phonons in crystals standing waves or traveling waves?
  12. E

    Crystal Structure: rc/ra = 1, <.23, >1

    What would be the structure of the crystal if rc/ra=1? hexagonal closed packed or anything else? What would be the structure of the crystal if rc/ra< .23 ? What would be the structure of the crystal if rc/ra>1 ?
  13. H

    Understanding Electron Effective Mass in Crystals

    I have got confused about electron effective mass in crystals. Which of the definitions below are correct? 1) When an electron is in a crystal with periodic potential, it behaves such as a free electron with effective mass m^* 2) when an external force is applied on the electron in a...
  14. R

    How do conduction-band electrons affect heat transfer in conductors?

    Hello. I am about to show how heat is transferred through crystals i. e metals I know that it should be about conduction, and that the single quantum oscillators start vibrating in higher modes, due to the extra energy. Now is the question: HOW exactly is the energy trasnferred...
  15. 1

    Bonds in Semiconductor crystals

    Hi! I study semiconductors and I am confused with the bonding picture for semiconductor crystals. For example, it is said that in Si crystal one can find covalent bonds. In the most books this bonds are shown like that: 2D crystal structure where lines between atoms are a covalent bonds, each...
  16. N

    Types of Piezoelectric Crystals to Harvest Sound

    I am in the process of building a piezoelectric device to harvest sound with a frequency generator at one side of a plastic/glass tube which sends out a low frequency which is then picked up by a piezo disk which send the energy to an led which demonstrates hoe sound can be converted to...
  17. G

    Why do high-melt-point crystals melt so low in molten glass?

    I'm looking at a glass "recipe" that heats the raw ingredients to melt at 1550C. This seems to present a problem in that the raw ingredients include: Al2O3: melting point = 2072 C MgO: melting point = 2852 C And even SiO2 (the primary ingredient) has a melting point (range) of...
  18. C

    Thermochromatic liquid crystals, how do they change color?

    If you look at liquid crystals in things like moodrings and LCthermometers then you will notice that they can change color when heated. Now I have looked on the internet and found that it has to do with the The cholesteric (or chiral nematic) liquid crystal phase, where they align with each...
  19. A

    Antiferromagnetic crystals with F and Cl

    I was just looking over a general list of antiferromagnetic crystals and couldn't help but notice that half the list were fluoride or chloride compounds which are often corrosive or otherwise problematic from a handling point of view (eg FeF2). This may seem a stupid question, but, are these two...
  20. J

    Understanding the Factors Behind Solid Crystal Structures

    Just wondering - What factor decides whether a solid takes up a crystalline structure or an amorphous structure? And if it takes a crystalline structure , what decides if it will be cubic, tetragonal, hexagonal , trigonal, monoclinic or triclinic?
  21. W

    Upper limit of Miller indices of BCC and FCC crystals?

    does anybody know the upper limit of the bcc and fcc metals like Fe, Cu, Ag? According to the fact that the planes with high (hkl) indices have small interplanar spacing d_hkl, the smallest spacing would be present. what is that? atomic diameter of a specifc metal?
  22. B

    Time Crystals Possible-maybe

    Classical Time Crystals Alfred Shapere and Frank Wilczek We consider the possibility that classical dynamical systems display motion in their lowest energy state, forming a time analogue of crystalline spatial order. Challenges facing that idea are identified and overcome. We display...
  23. R

    How do I turn FeCl3•6H2O crystals into 0.5M solution?

    Sorry if this is a dumb or noob question, but I have some FeCl3•6H2O crystals, and I want a 0.5M solution. How do I do it?
  24. F

    Crystals: difference between basis and unit cell

    Hello Forum, a lattice is a set of points. We can place a basis at each set of points. The basis can be one atom or a group of atoms. I thought that a translation of the basis would produce the whole crystal... How is a basis different from the unit cell? Are they the same thing...
  25. F

    Spontaneous emission in photonic crystals

    Hello forum, I have a question about photonic crystals. From Wikipedia: "photons (behaving as waves) propagate through this structure - or not - depending on their wavelength. Wavelengths of light that are allowed to travel are known as modes, and groups of allowed modes form bands...
  26. N

    Why are most of the ionic crystals Diamagnetism

    Why are most of the ionic crystals Diamagnetism ?? Ionic crystals are those crystals that are related to ionic bonds of atoms such as sodium chloride NACL
  27. N

    Crystals and Mood: Debunking the Healing Powers Myth

    What about the claim that crystals can heal or change moods? Total B.S?
  28. W

    Isotropic crystals & anisotropic crystals

    Alright my question is: why do single crystals properties vary with direction (anisotropic) when it is a perfect crystalline structure. I mean doesn't that mean that the atoms are ordered correctly so shouldn't that mean that at every direction its the same magnitude? I really need help because...
  29. M

    Chiral nematic liquid crystals - describing light diffraction

    So my book has an equation describing the wavelengths of light that are diffracted by a chiral nematic liquid crystal in terms of the refractive index (n), the pitch of the helix (p), and the angle (θ) with respect to the surface. The equation is this - λ = np√((1-cos2θ)/n2) If this isn't...
  30. C

    Why are there crystals formed when a hot saturated solution is allowed

    Homework Statement why are there crystals formed when a hot saturated solution is allowed to cool? the solid has already dissolved into the solution, forming the solute, so when the solution is cooled, and the temp decreases. does this mean they dissolve out of the solution? (i know...
  31. X

    Diffusivity problems in cubic crystals

    Hi all: I encountered a problem when studying the diffusivity of Li atoms in Si crystals. From the textbook, it is shown the diffusivity tensor in the cubic crystals (BCC FCC) is a diagonal matrix and the values along different directions are also the same (from the rotational symmetry), which...
  32. M

    Magnetism dielectric crystals

    What is origin of magnetism in dielectric crystals?
  33. S

    Monopolar polarization of crystals

    This one article mention such strange issue as monopole polarization in highly asymmetric crystals. (I did not read entire article). I always thought that polarization could be only dipolar because you need to get charge separation.How monopole thing could exist in a crystal?
  34. M

    Quiver path algebra and F-term relations in melting crystals

    EDIT: fixed TeX issues Hi, I'm learning about the correspondence in string theory between the geometry of Calabi-Yau manifolds and melting crystals. I care more about the math and know almost nothing about string theory, so navigating the literature littered with so much string theory jargon...
  35. W

    Valence electrons and Photonic crystals

    Hello PF, I came across a fact that, tungsten, molybdenum and chromium all have 6 valence electrons. Now,if one uses Molybdenum and Chromium instead of tungsten in photonic crystals for TPV(Thermo PhotoVoltaics) does it mean: 1. All are capable of releasing equal number of photons...
  36. M

    Calculating Yield of CuSO4 Crystals from Reaction of H2SO4 and CUO

    I was tasked to calculate the yield of CuSO4 by the reaction of H2SO4 and CUO. My equation says the it should get CUSO4 and H2O. But should we use CUSO4.5H2O for theoretical yield instead since it is a crystal that we are calculating - if so then I could not balance the equation... what...
  37. S

    Diffraction of x-rays by crystals

    :shy: By looking at the figures showing diffration of x-rays by crystals, it looks more like reflection.. Seems like I am studying reflection... So, where is the diffraction part??
  38. B

    Electron diffraction from crystals

    why is it that in electron diffraction from cystals, theta i and theta r are not necessarily equal?
  39. M

    Electrons diffraction in crystals

    Hello everyone, It's said that the first Brilloin zone is the k-space where electrons are not diffracted. Electrons with k-vectors on the surface of BZ are diffracted. How can we understand in terms of electron particules the behavior of electrons associated waves when these waves...
  40. R

    Is the Energy Band of Wood vs Crystals similar?

    　 Is the Energy Band of Wood vs Crystals similar? 　 As I understand it. In crystals the interaction of the atoms are more intimate.. meaning all the atoms in the crystals can influence one another which produced solid energy band. While in wood, the distance are further and hence the...
  41. B

    Crystals- filling a tetrahedral site.

    Homework Statement I'd like to work out what the largest sphere I could fit in the tetrahedral interstitial site of a cubic unit cell. Preferably I believe I need an expression in terms of the lattice constant a. Homework Equations The Attempt at a Solution The tetrahedral site...
  42. Useful nucleus

    Surface definition in crystals question

    I read the following paragraph about surface definition" "Each surface is specified by at least two pieces of information.Firstly, there are the Miller indices (hkl) of the plane that defines the orientation of the bulk cleavage. Secondly, there is the so-called shift - i.e. the displacement of...
  43. K

    Can Quartz Crystals Really Store Unlimited Data for an Unlimited Time?

    I have heard that Quartz crystals are able to store data and information in vast amounts. Is this possible and if so does it work?
  44. W

    LED from Silicon Carbide crystals

    Hello. I am interested in making homemade LEDs in the manner described here: http://www.popsci.com/diy/article/2010-02/gray-matter-light-mystery Could this work with silicon carbide sandpaper instead of the crystal form? If so, would I want to go for a lower grit to improve the chances of...
  45. E

    How big should sugar crystals get?

    Should it grow indefinitely ?(assuming you have a permanently super-saturated solution) Or does it stop growing when it reaches a certain mass or something ? If so why ? Also, has anyone had success in growing huge sugar/sucrose crystals (if yes, then would you please post up some...
  46. K

    Chemistry Determining Intermolecular Forces - Ionic Crystals and Network Solids?

    Homework Statement This is the worksheet: http://webcache.googleusercontent.com/search?q=cache:9jyqtuswY1AJ:www.chemmybear.com/groves/apch13_imfans.doc+ap+chem+pasadena+imf%27s&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a Homework Equations None, as far as I know The Attempt at a...
  47. S

    Practical question- anyone w. experience w. BBO crystals?

    hi all- having a strange (perhaps expected?) problem inserting a BBO into the optical path of a TiSaph fs laser. the issue is that i can achieve strong SHG output, but only with *severe* spatial distortion of the pulse shape. has anyone had experience/encountered this issue in an...
  48. W

    The effect of a magnetic field on the growth rate of crystals

    Hello I am currently researching on crystals and how their growth rate is affected by magnetic fields for my upcoming lab. Most of the information is based on labs but I quite don't understand what they speak of. So I was wondering if anyone here has any nice reading material on crystals and...
  49. W

    Stability of quasi low-dimensional crystals?

    We learn in solid state physics that crystals cannot exist in one or two dimensions. The main enemy of low-dimensional crystals is the acoustic phonon (Goldstone mode). Due to its small energy in the long wavelength limit, it contributes signifiantly to the fluctuation of the atomic position...
  50. J

    Are blocks (billets) of metal crystals?

    I work as a machinest and Mill mostly aluminum. I was wondering if the billets are Aluminum its crystalline form? Or just lots of Aluminum atoms held together by Metallic bond? thank you. Attached is a photo of Aluminum Block.
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