These 2 constructively Interfere good signal d Bragg s Law These 2 destructively Interfere bad signal d n 2dsin Just needs some satisfaction X Ray Diffraction XRD equipment Solution satisfied at specific angles n MUST be an integer Detector typically moves over range of 2 angles X r a det y ect or n 2dsin n d sin XRD machines vary angle as 2 because that angle is always relative to incident X ray beam trajectory 2 2 X ray source Typically a Cu or Mo target 1 54 or 0 8 wavelength Sample holder Orientation of diffracting hkl planes in sample A number of these are possible XRD Part II Theoretically almost an infinite number of planes can exist but certain ones diffract more strongly Related to the atomic density both of of atoms and in those ions atomic density XRD results Diffraction pattern Higher symmetry fewer more intense lines because multiple planes are complimentary identical d spacings for different planes yields identical diffraction XRD extinctions Some forms exhibit extinctions when planes should be present i e satisfy Bragg s Law but are not due to destructive interference with another plane s diffraction Useful for determining special conditions of symmetry in a single crystal ID for body face centered minerals as well as ones with screw axes and glide planes method to see differences between space groups XRD analyses Can look at minerals as single crystals or as a powder Single Crystal must be careful about orienting the crystal so Bragg s Law is satisfied use several different techniques advanced machines manipulate the sample in 3 axes x y z to catch all the peaks required for structural determination Powder has many particles with planes at many different orientations many orientations satisfy Bragg s Law intensities and locations 2 are characteristic of specific minerals Technique primarily used for identification Powder XRD analyses With a single crystal alignment of planes which give strong diffraction returns is very exact requires precise alignment With a fine powder idea is to have crystals at a wide variety of orientations so hitting that exact alignment is possible without manipulating the sample i e in a powder we figure a few grains are lined up correctly Powder X ray Analyses XRD analysis of a powder is a common quick and relatively easy way to identify minerals Having a mixture of minerals can be tricky so grains are first separated if possible small amounts of other minerals will give other peaks but intensities are low enough that it is not a big deal Do lose the ability to see the details of the structure of the mineral however as the precise alignment of the mineral giving the peak is unknown and not changeable Analytical Techniques for Minerals XRD X ray diffraction is one of the most powerful tools for mineral identification structural chemical refinement and size determination Microscopy Optical techniques are another very powerful tool for mineral identification identification of physical chemical history of minerals rocks and mineral association which we will also study in detail both lecture and lab More analytical techniques Electron microscopy look at techniques which utilize how electrons shot through a sample of mineral interact with minerals imaging possible to very small sizes Scanned proximity probe microscopy techniques look at forces between probe tip and sample to measure a property height optical absorption magnetism etc Spectroscopy different methods of studying how different parts of the electromagnetic spectrum of which visible light is a small part are affected by minerals More analytical techniques Sychrotron Different techniques including many spectroscopic techniques that utilize particles accelerated to very high speeds and high energies Magnetic different techniques that utilize the magnetic properties of minerals Size techniques to determine the sizes of different minerals Chemistry isotopes techniques to probe chemical and isotopic signatures in minerals Spectroscopic techniques investigate the interaction of some part of the electromagnetic spectrum with a material Each technique provides different information about the chemistry structure and physics of the material Spectroscopic Techniques Utilize the absorption or transmittance of electromagnetic radiation light is part of this as is UV IR for analysis Governed by Beer s Law or Beer LambertBouger law but everyone likes Beer A abc Where A Absorbance a wavelengthdependent absorbtivity coefficient b path length c analyte concentration Spectroscopy Exactly how light is absorbed and reflected transmitted or refracted changes the info and is determined by different techniques sample Transmittance spectroscopy Reflected spectroscopy Raman Spectroscopy Light Source Light shining on a sample can come from different places in lab from a light on a plane from a laser array or from earth shining on Mars with a big laser Can tune these to any wavelength or range of wavelengths IR image of Mars Olivine is purple Causes of Absorption Molecular or atomic orbitals absorb light kicks e from stable to excited state Charge transfer or radiation color centers Vibrational processes a bond vibrates at a specific frequency only specific bonds can absorb IR though IR active Vibrational spectroscopy Another name applied to absorption spectroscopy in IR range and for Raman spectroscopy Sensitive to the vibrational modes of bonds between atoms rather than of the ions themselves Optical Spectroscopy Techniques concerned with how light reflects absorbs or transmits through minerals from near UV to mid infrared 250 3000 nm wavelengths Dealing with energy which excited electrons from a standard to an excited state Spectroscopy Exactly how light is absorbed and reflected transmitted or refracted changes the info and is determined by different techniques sample Transmittance spectroscopy Reflected spectroscopy Raman Spectroscopy Reflectance Spectroscopy Can be optical or vibrational Non destructive form of analysis used to see some of the chemistry bonding Spectroscopy is particularly good at detecting water and OH groups in minerals especially in IR Good at differentiating between different clays because it detects OH groups well Raman Spectroscopy Another kind of spectroscopy which looks at a scattering effect and what that tells us about the chemistry oxidation state and relative proportions of different ions M ssbauer Spectroscopy Special effect restricted to specific isotopes of certain