A controversial quarry project could generate up to £190m for Cornwall's economy, claims a report.
Shire Oak Quarries wants to mine gabbro from Dean Quarry near St Keverne, which has been shut for seven years.
It is hoped the rock will be used to build a sea wall for a tidal energy project in Wales.
But some local people fear it will cause damage to the environment and livelihoods.
Although no contract is currently in place, if Dean Quarry is chosen as a supplier, gabbro would be transported by barges from the mine to Swansea where it would act as armour for a sea wall.
The six-mile wall would create a lagoon with turbines to harness the power of the tides and generate electricity.
Shire Oak Quarries, which has planning permission for the revamped quarry, aims to extract up to 1.2 million tonnes of stone a year over the next three years.
It commissioned a report by consultant economist Kevin Butler which said it would inject between £140m and £190m into the local economy and create 50 full-time jobs.
Mr Butler said: "It would create new, well paid, non-seasonal jobs and the intention is that the majority of its operating budget would be spent locally, ideally within a 25-mile radius of the quarry. This would create a net positive impact valued at millions of pounds a year."
Cornwall Against Dean Super Quarry is seeking a judicial review into the plans, saying it will affect a marine conservation zone and drive tourists away.
They say that the stone should be imported from Norway instead.
Tim Van Berkel from the Cornish Seaweed Company which harvests in the area, believes the quarry would affect his firm as well as others such as diving and sea salt firms.
"There are going to be big ships coming to the area and if there is an oil spill we would suffer," he said.
"They are also going to dredge the area and it will have a huge impact."
Shire Oak Quarries says it has no plans for dredging and that a full Environmental Impact Assessment would be submitted with any application for marine infrastructure works.