What is a Quarry?4 min read

What is a quarry?

A quarry is an open surface excavation from which stone is extracted for use in construction. Unlike a mine, which follows a seam underground, a quarry is normally worked from the surface downwards, cutting benches into the rock face. Quarries supply everything from crushed aggregate for concrete through to the large blocks of dimension stone used on building facades.

For any project using natural stone, the quarry is where quality is decided. The colour, the veining, the soundness of the material and whether there is enough of it to finish the job are all determined at the rock face, long before anything reaches the building. That is why it is the first place we go.

Dimension stone quarries and aggregate quarries

Not every quarry does the same job. The distinction that matters for construction is between quarries producing crushed stone and those producing dimension stone.

Feature	Dimension stone quarry	Aggregate (crushed stone) quarry
Product	Large intact blocks, cut to size and finished	Crushed rock of graded particle sizes
Extraction method	Diamond wire and belt saws, jet piercing, light selective blasting	Heavy blasting and mechanical crushing
Priority	Keeping the stone intact, and matching colour and vein	Volume and throughput
Typical end use	Facade cladding, flooring, paving, monuments	Concrete, asphalt, road base, ballast
Value per tonne	High; a single block can be worth thousands	Low; value is in bulk

Most quarries are capable of producing either product, and a crushed stone quarry can be converted to dimension stone production. The difference lies in the method. Aggregate can simply be blasted and crushed, whereas dimension stone has to be separated intact using more precise and delicate techniques such as diamond belt saws, burners (jet-piercers), or light and selective blasting with Primacord, a weak explosive.

How is dimension stone extracted from a quarry?

Extraction is a slow, deliberate process. The aim is not to break rock but to release it whole.

1. Overburden removal. Soil and weathered rock above the sound stone are stripped away to expose workable material.
2. Benching. The quarry is worked in steps, or benches, giving safe access to the face and a predictable geometry to cut from.
3. Freeing the megablock. A large mass of stone is cut free from the face on several sides, using diamond wire saws, chain or belt saws, or jet piercing. These huge ‘megablocks’ provide the first real indication of the colour and veining the deposit will yield.
4. Toppling. The freed mass is eased away from the face and lowered onto a prepared bed of debris, which cushions the fall and prevents it shattering.
5. Squaring into blocks. The megablock is cut down into smaller, more manageable squared blocks, maintaining the vein arrangement so the material can later be laid out in the correct sequence.
6. Grading and selection. Blocks are assessed and set aside by quality, colour range and suitability. Not every block will meet the design.
7. Transport to the fabricator. Selected blocks are shipped for sawing into slabs and finishing.

What happens during a quarry inspection?

A quarry inspection is the earliest and most valuable point at which a project can control its stone. Once material has been sawn, finished and shipped, the options for putting a problem right narrow sharply and the cost rises with every stage it passes. Working at the quarry, we typically:

• Assess newly felled blocks against the architect’s design criteria for colour, tone and vein arrangement.
• Check the soundness of the material and reject blocks with fissures, staining or inclusions that will not survive fabrication.
• Confirm the deposit can actually yield the quantity the project needs, in a consistent range, for the whole package.
• Monitor tooling and cutting practice, since how a block is freed affects what can be got out of it.
• Verify identification, packing and loading before the stone leaves the site.

Read more about our independent natural stone inspection service, which runs from the quarry through to final installation.

Quarries we have worked in

Our consultants work at the rock face wherever a project’s material originates. For the Ronald O. Perelman Performing Arts Center in New York, we selected Estremoz marble megablocks at the quarry in Portugal, assessing each one for the vein arrangement the architects required before it was committed to production. For Renzo Piano’s Valletta City Gate in Malta, more than 12,000 cubic metres of Maltese Upper Coraline hardstone limestone were quarried on the islands, a short distance from the building itself.

Further Reading…

Read our guide to dimension stone, its types and uses.

Read about why a project needs a stone consultant.