01Specimen sheet
Sand, gravel and crushed stone, explained plainly
Aggregates sit under almost every road, floor, drain and garden path. This is an independent, sourced guide to what they are, how they are made and graded, what they are used for, and the health and environmental questions around them.
02The grade ladder
Six size classes, smallest to largest
Before anything else, a word about size. Geologists sort loose material by grain diameter, and the names we use for it (clay, silt, sand, gravel) mark steps on that ladder.
- ClayUnder 4 micrometres
- Silt4 to 62.5 micrometres
- Sand62.5 micrometres to 2 mm
- Gravel2 to 64 mm
- Cobble64 to 256 mm
- BoulderOver 256 mm
Size classes follow the Wentworth grade scale, as set out by the U.S. Geological Survey and the Washington State Department of Ecology. The grading plate explains how builders use size in practice.
03Three main plates
Begin here
- 01Open
What aggregates are and how they are made
The foundation page: natural and crushed material, how it is dug, crushed, screened and washed, and what it goes into.
- 02Open
Aggregate Sizes, Grading and Choosing Material in General Terms
Size classes, sieves and gradation curves, and how to think about choosing material for a job in general terms.
- 03Open
Silica dust and quarry safety as public bodies state it
What NIOSH, OSHA and MSHA say about respirable crystalline silica, and why your own regulator has the last word.
04Index of uses and topics
Ten shorter plates
- 04Sand types and usesNatural, manufactured and industrial sand, and what shape and cleanliness change.
- 05Gravel for drives and drainsWhy angular stone locks together, why rounded stone shifts, and how drainage stone differs.
- 06Crushed stone basesThe hidden layer under paving and slabs, and why fines and compaction matter.
- 07Concrete and mortarThe ingredients, the job each aggregate does, and why clean, graded material matters.
- 08Play sand safetyWhat public bodies say about sand where children play.
- 09Pool and filter sandHow a sand filter works and what public guidance says about filter media.
- 10Recycled aggregatesCrushed concrete and reclaimed asphalt as public bodies describe them.
- 11RehabilitationHow extraction affects land, water and habitat, and what restoration looks like.
- 12How quarries are regulatedThe kinds of rule that apply, with examples by country.
- 13Reading a delivery ticketGross, tare and net, tonnes and cubic yards, and measuring a volume.
05A note on safety
Dust is the one hazard worth reading about first
Cutting, crushing and sweeping dry mineral material can raise fine dust, and public health bodies have specific things to say about the crystalline silica that some of it contains. We set out what they say and where to find the rules that apply to you on the silica dust and quarry safety plate. This site cannot tell you what is required at your workplace or on your site. Your own regulator can.