Implications of surface weathering of rapakivi granite outcrops for natural stone evaluation were studied in the Wiborg rapakivi granite batholith in southeastern Finland. The study was performed as field mapping, comprising the whole batholith and as detailed investigations on selected outcrops. The Wiborg batholith is composed of wiborgite, pyterlite, even-grained rapakivi granite, porphyritic rapakivi granite, porphyry aplite, and gabbro-anorthosite. Wiborgite is the main rapakivi granite type. Weathering affects coarse-grained rapakivi varieties: wiborgite, pyterlite, and porphyritic rapakivi granite. Weathering occurs as surficial weathering of outcrops and randomly along subhorizontal and subvertical fractures, and varies in intensity. In the weathered upper parts of the outcrops the colour of the stone is altered and soundness of the stone diminished, which has a significant impact on the natural stone evaluation. In rapakivi granite areas, subsurface evaluation methods, by which the weathered surface part of the outcrops can be recognized, should always be used. Development of subsurface methods is required in order to make them more applicable in the evaluation of natural stone in areas with weathered rock.
Rapakivi granites were in use during the Middle Ages in Finland. Their most spectacular use, however, was for structures built in St Petersburg between 1760 and 1917. Remarkable examples are the majestic and slender Alexander Column and the 112 columns of St Isaac's Cathedral. All Rapakivi granite was extracted from the Wiborg Rapakivi granite batholith in several quarries around the municipality of Virolahti in SE Finland (old Russia). Today, the 1640 Ma-old Wiborg batholith is the most important area for natural stone production in Finland and in the Leningrad region, Russian Federation. The main quarried stone varieties of Rapakivi granite (Baltic Brown, Baltic Green, Carmen Red, Karelia Red, Eagle Red and Balmoral Red) are regularly produced in large quantities in Finland for the global stone market due to the stone's unique qualities. Examples of applications in Rapakivi granite from Finland can be found in the USA, China, South Africa, the UK, Italy, Austria, Ireland, Spain and Germany as well as in Scandinavia and Russia. There are also quarries near Vyborg, the Russian Federation: Vozrozhdenie and Ala-Noskua.
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