D-Spacing
Definition
The perpendicular distance between adjacent parallel planes of atoms in a crystal lattice, measured in angstroms or nanometres. Each set of planes in a mineral has a characteristic d-spacing that appears as a peak at a specific 2-theta angle in a powder diffractogram.
- Unit of measurement
- Angstroms or nanometers
- What it describes
- Perpendicular distance between adjacent lattice planes in a crystal
- Role in forensics
- Creates a unique diffraction pattern signature for each mineral species
Common questions
What is d-spacing and why does it matter in forensics?+
D-spacing is the perpendicular distance between adjacent parallel planes of atoms in a crystal lattice, measured in angstroms or nanometers. It's forensically important because each mineral species has characteristic d-spacings that produce unique diffraction patterns, allowing you to identify soil minerals, glass fragments, and other crystalline materials through X-ray diffraction.
How does d-spacing relate to X-ray diffraction patterns?+
When X-rays hit a crystal, the d-spacing of its lattice planes determines the angle at which diffraction occurs, according to Bragg's law. In a powder diffractogram, each d-spacing appears as a peak at a specific diffraction angle (2-theta), and together these peaks form a unique fingerprint for identifying the mineral.
How do I use d-spacing to tell minerals apart?+
Different minerals have different arrangements of atoms and therefore different d-spacings. By running an X-ray diffraction test and measuring the peaks (which correspond to d-spacings), you get a pattern unique to each mineral species, making it possible to distinguish soil particles, clay minerals, or trace evidence with confidence.
Related terms
- Bragg's Law
- nλ = 2d sin(θ). A monochromatic X-ray beam diffracted off the parallel lattice planes of a crystal produces constructive interference only at...
- Anode Target
- The metal block (commonly Cu, Mo or Rh) that electrons strike inside an X-ray tube to produce the X-ray beam. Choice of...
- Basal Reflection
- The diffraction peak arising from the repeat distance along the stacking direction of clay layer silicates (the c-axis or 001 reflection). Its...
- Bromobenzene
- C6H5Br, density 1.50 g/cm3; the lighter component of the forensic density-gradient liquid mixture.
- Bromoform
- CHBr3, density 2.89 g/cm3; the denser component of the forensic density-gradient liquid mixture, used to create the bottom of the density range.
- Characteristic X-Rays
- Sharp emission lines produced when an inner-shell vacancy in an atom is filled by an outer electron. Their energies are element-specific (Moseley's...
- Continuous (Bremsstrahlung) Radiation
- Smooth background X-ray spectrum produced when high-energy electrons decelerate in the anode. Element-independent. The 'hump' under the characteristic lines.
- Density-Gradient Column
- Glass column filled with stepwise layers of liquids of decreasing density (commonly bromoform 2.89 g/cm3 and bromobenzene 1.50 g/cm3 mixed in known...
- Diatom Frustule
- The siliceous cell wall of a diatom, composed of biogenic opal; species-specific in shape and ornament, and resistant to degradation in soil...
- EDXRF
- Energy-dispersive X-ray fluorescence. A solid-state detector resolves the entire emission spectrum at once by photon energy. Cheap, portable, faster.
- Forensic Palynology
- The application of pollen and spore analysis to legal investigations. A forensic palynologist identifies the species composition of pollen assemblages from crime-scene...
- Heavy-Mineral Fraction
- The sub-fraction of soil mineral grains with density above 2.85 g/cm3, including pyroxene, hornblende, garnet, zircon, rutile, and tourmaline; particularly diagnostic of...
Explained in these topics
- Soil Examination: Density Gradient, Mineralogy and PalynologyThe interplanar distance in a crystal lattice (units: angstroms or nm), which determines the diffraction angle for a given X-ray wavelength via Bragg's law; un...
- X-ray Techniques in Forensic Analysis: XRD, XRF and X-ray ImagingThe perpendicular distance between adjacent lattice planes in a crystal, expressed in angstroms. A diffraction pattern is essentially a list of d-spacings uniq...
- X-ray Diffraction and Clay MineralogyThe perpendicular distance between adjacent parallel planes of atoms in a crystal lattice, measured in angstroms or nanometres. Each set of planes in a mineral...