Inside the USGS Bascom Laser Diffraction Sedimentology Laboratory

Ice-contact subaqueous fan deposits studied at and around Fort Drum, New York. USGS / Grant Colip.

What the laboratory does

The Bascom Laser Diffraction Sedimentology Laboratory, in the Florence Bascom Geoscience Center at U.S. Geological Survey (USGS) headquarters in Reston, Virginia, characterizes sediment in detail, working with other USGS centers, state geological surveys, industry, universities and other partners. Its tools:

• laser diffractometry, for precise particle-size analysis;
• portable X-ray fluorescence (XRF), for the elements in rock or sediment, in the lab or field;
• petrographic microscopy;
• mechanical sieve analysis;
• instruments for magnetic susceptibility and conductivity, and equipment to break up clays, burn off organic matter in a muffle furnace, and heat, chill and dry samples.

It analyzes soil and sediment cores from land, sea and lakes, coastal surface sediments and carbonate materials — work behind geologic mapping, resource assessments, land change studies and geohazard analyses.

A sediment core's grain-size profile: the share of clay, silt and sand down the core. USGS.

Laser diffraction

The lab runs a Beckman Coulter LS 13 320 XR and a Malvern Mastersizer 3000E. Samples circulate in a liquid, where laser beams produce a diffraction pattern from which each sample's particle-size distribution is calculated. Adding polarization intensity differential scattering (PIDS) — vertical and horizontal polarized light at about 450, 600 and 900 nanometers — covers particles from 10 nanometers to 3.5 millimeters. (Product names are for description only, not endorsement.)

Laser diffraction equipment for particle-size analysis. USGS / Grant Colip.

It handles core and borehole material, critical-mineral deposits, map-unit samples, deep-sea sediments, aggregates and engineering materials, lake and river sediments, soils and paleosols, storm deposits, heavy-mineral sands, dune and delta sands, carbonates and near-shore deposits.

Particle-size distributions of lake mud, river sediment and dune sand. USGS.

What it's used for

• Surficial geologic mapping: grain size, sieving and XRF describe Quaternary map units — increasingly important for critical minerals, economic development, water and resource security, aggregates and infrastructure. Ongoing (2026) mapping funded by the National Cooperative Geologic Mapping Program at and around Fort Drum, in Jefferson and Lewis Counties, New York, has USGS working with the Department of Defense on infrastructure, aggregates and groundwater.
• Soils, aggregates and infrastructure: grain size shapes how soils and aggregates behave — their hydrology, suitability for engineering, and how easily they erode. Pairing lasers with sieves covers round grains and odd shapes alike, such as organics and platy clays, for civil engineering, agriculture and geotechnical surveys.
• Carbonate sedimentology: grain-size and sorting trends, with microscopy, distinguish times of high sea level (highstands) in dune deposits in the Bahamas and other coasts — useful for sediment-transport models and coastal geomorphology.
• Storms and coastal resilience: storm deposits help predict storm impacts, trace storms through the late Holocene, and inform land-use decisions. The lab measured deposits from Hurricane Irma, a Category 4 storm that hit Everglades National Park and the Florida coast in 2017, with the National Park Service and the Army Corps of Engineers.
• Biostratigraphy: grain size tied to microfossil zones across shallow-to-deep marine transects reveals past geography and oceans. Cores from South Carolina's coastal plain, compared with Long Bay sediments, map where sand eroded and settled and find hiatuses — gaps in deposition. States use offshore sand for beach replenishment and as a possible source of heavy minerals.

Mineral grains in dune sand. USGS / Grant Colip.

The same coast before (April 2014) and after (January 2018) Hurricane Irma. USGS / Lynn Wingard.

Grain size in a Long Bay core, correlated with nannofossil zones, formations and ages. USGS / Kristina Gardner.

Sources

Based on Bascom Laser Diffraction Sedimentology Laboratory, Reston, Virginia, U.S. Geological Survey Fact Sheet 2025–3051, USGS Publications Warehouse; a work of the United States government in the public domain.