XRD
Definition
X-ray diffraction. Identifies crystalline mineral phases (quartz, feldspar, kaolinite, montmorillonite, calcite) by their characteristic d-spacings via Bragg's law. The mineral assemblage is one of the most discriminating soil features.
- Full name
- X-ray diffraction
- Identifies
- Crystalline mineral phases
- Physical principle
- Bragg's law and characteristic d-spacings
- Example minerals
- Quartz, feldspar, kaolinite, montmorillonite, calcite
- Forensic value
- Mineral assemblage is highly discriminating for soil
Common questions
Why is XRD combined with elemental techniques rather than used alone for soil comparison?+
XRD identifies which crystalline minerals are present but says nothing about trace element content, while XRF or ICP-MS quantify elements but cannot identify mineral structure, so combining the two gives a fuller and more discriminating soil profile than either technique alone.
Can XRD analyse amorphous soil components such as organic matter?+
No. XRD depends on a regular crystal lattice to produce a diffraction pattern, so amorphous materials and organic matter produce no useful signal and must be characterised by other methods, meaning an XRD result describes only the crystalline mineral fraction of a soil sample.
Related terms
- 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...
- Loss on Ignition (LOI)
- Weight loss after heating dried soil to 550 degrees Celsius. Approximates the organic matter content. A simple, cheap, high-yield discriminator in field...
- Munsell Soil Colour
- Standardised colour notation written as hue, value and chroma (e.g. 10YR 4/3 dark brown). Read by holding a moist soil sample against...
- Regur (Black Cotton Soil)
- Indian Vertisol formed on Deccan basalt. High in smectite (montmorillonite) clay, deep black colour, swells and shrinks dramatically with moisture. Major signature...
- Soil
- Weathered surface layer of earth made of mineral particles, organic matter (humus), water, air and living micro-organisms. The forensic interest is in...
- USDA Texture Triangle
- Ternary diagram that classifies soils by relative proportion of sand (2.0 to 0.05 mm), silt (0.05 to 0.002 mm) and clay (less...
- XRF and ICP-MS
- Elemental techniques for the trace-metal fingerprint (Fe, Ti, Mn, Cr, Ni, V, rare earths). XRF (often EDXRF) is non-destructive; ICP-MS is destructive...