Diatom Frustule
Definition
The siliceous cell wall of a diatom, composed of biogenic opal; species-specific in shape and ornament, and resistant to degradation in soil and sediment for geological timescales.
- Material
- Siliceous (biogenic opal); glass-like and highly resistant to decay
- Forensic value
- Species-specific shape and ornament make diatoms traceable to their source environment
Common questions
What is a diatom frustule made of?+
A frustule is the siliceous (glass-like) cell wall of a diatom. It's composed of biogenic opal, which makes it extremely hard and durable. This glass structure is what allows frustules to survive in soil and sediment long after the diatom dies.
How does a frustule help identify a diatom species?+
Each diatom species has a frustule with a unique shape and pattern of ornaments (tiny surface details). This makes frustule morphology highly species-diagnostic. Forensic examiners can use these distinctive shapes to identify which species of diatom is present in a sample.
Why are frustules useful in forensic investigations?+
Frustules are resistant to degradation for geological timescales. Because they survive long after the diatom dies and persist in sediment and on organic material, they can be recovered from soil, sediment, and other samples as evidence. Their species-specific forms provide a clear link to the environment where they came from.
Related terms
- Acetolysis
- Erdtman's 1934 extraction method. The sample is treated with a 9:1 mixture of acetic anhydride and concentrated sulphuric acid, which dissolves cellulose...
- 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.
- D-Spacing
- The perpendicular distance between adjacent parallel planes of atoms in a crystal lattice, measured in angstroms or nanometres. Each set of planes...
- 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...
- 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...
- Indicator Species (Pollen)
- Pollen taxa with restricted geographic ranges or specific habitat requirements, contrasted with background species that occur everywhere; indicator species provide site-specific geographic...
- Laser Diffraction (PSD)
- A particle-size analysis technique that measures the angular distribution of laser light scattered by suspended particles to produce a continuous grain-size distribution...
- Murray-Tedrow Framework
- The tiered forensic-soil comparison protocol established by Raymond Murray and John Tedrow in their 1992 text 'Forensic Geology,' which organises soil examination...
- Palynomorph
- Any acid-resistant microscopic organic particle recovered by palynological processing, including pollen grains, spores, dinoflagellate cysts, and fungal spores. Each type carries different...
- Phytolith
- Opaline silica body precipitated in or between plant cells during growth. Grass phytoliths are produced in high quantities and persist in soil...
Explained in these topics
- Finds and Artefact ProcessingThe siliceous cell wall of a diatom, which survives in sediment and on organic material long after the organism dies. Frustule morphology is highly species-dia...
- Soil Examination: Density Gradient, Mineralogy and PalynologyThe siliceous cell wall of a diatom, composed of biogenic opal; species-specific in shape and ornament, and resistant to degradation in soil and sediment for g...