Another quarry famous for it’s supply of granite used for building London is the Cheesewring Quarry on the south-eastern edge of Bodmin Moor, 1.5 kilometres north of the village of Minions. Adrian Spalding noted “The quarry worked the silver-grey granite of Stowe’s Hill, cutting deep into the hillside but stopping short of the famous Cheesewring stones. The hill is surmounted by a Neolithic hillfort, demonstrating the earliest identifiable use of granite as a building material.” He notes that “..the Duchy of Cornwall had placed restrictions on the 1845 lease to protect the “Druidical remains or natural curiosities” 
Quarrying ” .. continued on a substantial scale until the railway closed in 1916.” 
Stone from Cheesewring stone was used for both Tower bridge, the pillars, pilasters or piers of the cast iron Lambeth Bridges and Westminster Bridge, ‘London docks’ and the Embankment.  
Again it’s worth checking Ruth Siddall’s Embankment walk, as a reminder of the different Cornish granites  https://www.ucl.ac.uk/~ucfbrxs/Homepage/walks/Embankment.pdf
And Colin Bristow’s description here “The granite of the Cheesewring is a durable silver-grey granite, weakly porphyritic with feldspars about an inch long, intermediate between the finer and coarser varieties of Cornish granite (Reid et al. 1911). It has a feint foliation with a northerly dip. Occasional xenoliths containing andalusite and sillimanite are seen. The way in which the sub-horizontal joints parallel the surface and increase in frequency towards the surface is well seen in this quarry. The vertical joints are mineralized with quartz, tourmaline and small amounts of metalliferous minerals. ” 
Worth saying this area is packed full of industrial archaeology, old tin and copper mines (as well as quarries) of the Caradon Mining District! 
Getting there :
There is a a Monday-Saturday bus routes, 73, 74, 236 that go to Darite or Upton Cross and you’ll have to walk from there, maybe an hour, but for someone interested in industrial archaeology that will be a bonus! https://www.gocornwallbus.co.uk/
Liskeard is on the mainline from Paddington. 4 hours. You could just do this as a day out!
A 6 miles steady uphill from Liskeard
Minions has 2 carparks. It’s half way between the A30 and A38.
 Conservation value of abandoned pits and quarries in Cornwall – Adrian Spalding http://spaldingassociates.co.uk/wp-content/uploads/2014/02/pits_quarries.pdf  https://www.cornwall.gov.uk/media/ybdlziqy/evidence-report-the-building-stones-of-cornwall-the-identification-of-heritage-quarries.pdf  http://londonpavementgeology.co.uk/location-details/?id=543
 https://archive.org/details/britishforeignbu00watsrich  https://www.ucl.ac.uk/~ucfbrxs/Homepage/walks/Embankment.pdf  The Geology of the building and decorative stones of Cornwall – Supplementary Publication – Granites and Elvans – Colin Bristow https://www.geolsoc.org.uk/~/media/Files/GSL/shared/Sup_pubs/2013/18675_file.rtf  https://www.cornishmineimages.co.uk/caradon-mining-district/