Edited from the Ronez website
There may be evidence of commercial quarrying in a 1651 reference to the Clos de Carieres in St John, where almost two centuries later Ronez Quarries were established when the Jersey Granite Company commenced operations there in 1869. A successor to this company was acquired in 1911 by the Croft Granite, Brick, and Concrete Company of Leicestershire.
In Guernsey there was a quarry at St Germain at the Castel in 1639 and in 1840 John Mowlem, founder of the famous civil engineering firm, renewed the paving of Blackfriars Bridge with setts of Guernsey granite. The repaving of London Bridge and the Strand followed, and the granite for the Thames Embankment, 1862-74, also came from Guernsey. By the end of the 19th century Mowlem's Guernsey operation had a steam crusher, and all the paraphernalia of weigh bridges, storage yards, workshops, stables, blondins and offices. In addition to the quarries they owned, they leased others.
In the 19th century the ports of St Helier in Jersey and St Sampson in Guernsey were important for the export of paving stones and chippings to the English mainland and by the early 1900s St John's quarries had acquired their own jetty, crane, mooring buoy and were on occasion loading three ships or more with aggregate.
19th Century Channel Island census returns speak of quarrymen, stone cutters, stone dressers, stone crackers, and stone miners, as well as stone merchants, and as the demand for stone grew, so labour had to be imported. Normandy and Brittany were obvious sources, but so were England and Ireland, and even Scotland. In 1886 the Stone Crackers Union was formed to defend the interests of quarriers. In 1911 it was superseded in Guernsey by a branch of the United Union of Quarrymen and Settmakers. In 1937 it was incorporated into the General and Municipal Workers Union, which was active through out the Channel Islands.
The German occupation of the Channel Islands from 1940-45 saw the requisition of the islands' quarries. The quarry manager at St John, because he was of British citizenship, was interned by the Germans in Bavaria for the duration of the war. In Guernsey, Mowlem's plant was brought back into use by the Germans. The quarries on both islands were worked by slaves brought over from mainland Europe by the Germans who built railways on both Jersey and Guernsey to deliver the crushed stone and cement needed for building Hitler's Atlantic Wall.
With the war over the quarrying on both islands had to undergo a long and expensive process of reconstruction and several quarries did not reopen, their rehabilitation being uneconomic. Croft engineers came to rebuild the St John plant and to build a new jetty. This gave opportunities for rationalization and technical advancement. Horses and carts and steam cranes gave way to huge excavators, dumper trucks and loading shovels. Electricity took over from steam.
In March 1961 the Jersey Cement and Granite Company commenced operations in Guernsey, thereby linking what was hitherto the separate quarrying traditions of the two islands. This was done by the acquisition of he quarries at Les Vardes, Bordeaux and Mont Cuet.
In 1963 ownership of the Jersey Cement and Granite Company was transferred from the Croft Granite, Brick, and Concrete Company, to English China Clays, and in 1966 in Jersey Western and L'Etacq quarries were purchased. At the same time the company extended its interests to Alderney, leasing land there at the Arsenal. A year later it changed its name to Ronez Ltd and in 1996 was acquired by CAMAS, which in turn merged with Bardon Aggregates to become Aggregate Industries. In March 2005 Ronez Limited as part of Aggregate Industries merged with the Holcim Group, an enterprise of Swiss origin which since it began in 1912 has achieved global status.