Nero Portoro

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Nero Portoro
Nero Portoro Bianco with numerous white and a few gold-colored veins (pattern approx. 12 × 8 cm)
Isola Palmaria viewed from the mainland

Nero Portoro is a black limestone whose occurrences range from Porto Venere to Marola near La Spezia in Liguria on the Gulf of La Spezia . With its gold-colored veining, this natural stone is in great demand and is one of the most exclusive decorative stones in the world.

Naming

The name of this natural stone is composed of "Nero" for its black color, "Porto" comes from the town of Porto Venere, which is close to the quarries, and "Oro" stands for the gold-colored veins.

In addition, a distinction is made between Porto Nero Giallo with golden yellow veins ( ital. Giallo = yellow) and the white veined Porto Nero Bianco . Another difference is made between fine (Portoro Macchia Fine) and coarsely veined stone layers (Portoro Macchia Grande) .

In older publications the name Portor di Portovenere can be found . The rock was also shipped to the United States by sea in the 19th century for representative purposes, at which time it became known under the trade name Black-gold .

Occurrence

The occurrence of Nero Portoro ranges from Porto Venere to Marola. This rock deposit is also found on the islands of Palmaria and Tino off Porto Venere . The islands and the quarry area on the mainland are part of the Cinque Terre UNESCO World Heritage Site . The active quarries on the Gulf of La Spezia, mostly located on the mountain ranges, are mostly operated underground. The mining of Nero Portoro in the mountains north of Porto Venere took place as early as the 1780s. By 1833 the quarry on the island of Tino was abandoned.

In the south of the island of Palmaria there is a historic quarry, in which Nero Portoro was previously mined. You can still see an old crane, a pulley system for transporting the stone blocks and the ruins of the workers' quarters.

geology

Nero Portoro was formed in the Lias during the unfolding of the Apennines about 175 million years ago. The rock formation took place close to the coast in a sea bay in which there was strong algae growth and plankton was found. A high carbon content could accumulate in this brackish water with a lack of oxygen and low wave movement . Since the dead plants and marine organisms produced digested sludge , the rock turned gray to black. Overlaying pressure and compaction resulted in limestone from the lime and clayey sludge. During manual work on the rock, Nero Portoro releases the odor of digested sludge, but this is no longer noticeable after processing.

Due to the compression and strong folding during its formation, strongly structured layers formed from rock fragments formed, which give this rock its typical decor.

Rock description

In the limestone there are veins of golden yellow, white or white-gray calcite . The golden yellow colored veins were created by the inclusion of limonite , a mixture of different iron compounds , and run through the rock as stylolites . The contrast of black and golden yellow color gives the natural stone its characteristic character.

The veins, which are folded in different degrees, are between 1 and 10 millimeters thick. The golden yellow color can partially merge into yellow-gray or white. The plates and workpieces that are exclusively black and gold in color are the most popular.

use

The golden yellow veined limestone, which is also traded under the incorrect name marble , is one of the more exclusive natural stones. Nero Portoro has been used since the Middle Ages. In the 18th, 19th and 20th centuries, this stone was mainly used in the arts and crafts for interior decoration objects, such as columns, plinths, chimney cladding, decorative panels on walls and bowls. A typical and more recent period of use is the Art Deco period . You often come across him on desk sets with fitted ink wells and vases. For a long time, the gold-colored type has mostly been used for table tops or as a wall covering, on furniture and as a floor covering in exclusive rooms. The block sizes are often relatively small due to the strongly fissured rock occurrence, often one cubic meter.

Nero Portoro can be polished to a high gloss, but loses its polish outdoors.

Usage examples

literature

  • Karlfried Fuchs: Natural stones from all over the world, discover, determine, use . Vol. 2. Munich (Callwey) 1997, ISBN 3-7667-1267-5 .
  • Friedrich Müller: International Natural Stone Index (INSK). 10th volume, 3rd edition 1993, Ebner Verlag, Ulm 1993.
  • Monica T. Price: Decorative stone, the complete sourcebook . London (Thames & Hudson) 2007, ISBN 978-0-500-51341-5 .

Individual evidence

  1. ↑ Müller: INSK. 7.1.7 (see literature)
  2. ↑ Heinrich Schmid : The modern marbles and alabaster, whose classification, origin, properties and use ... . Leipzig, Vienna (Deuticke) 1897, pp. 44–45
  3. ↑ Ludwig Friedrich Wolfram: Complete textbook of the entire architecture; First volume: Doctrine of natural building materials, first section. From natural building materials . Stuttgart (Carl Hoffmann), Vienna (Carl Gerold'sche Buchhandlung) 1833. p. 65
  4. ↑ Alois Kieslinger : The stones of the Vienna Ringstrasse . Steinerverlag, Wiesbaden 1972, p. 316
  5. ↑ Robert sailor and Herbert Summesberger: Wiener stone walking paths, the geology of the big city . Brandstätter, 1999, ISBN 3-85447-787-2 , p. 58
  6. ↑ Price: Decorative stone , 2007, p. 88
  7. ↑ Johannes H. Schroeder (Ed.): Natural stone in architecture and building history of Berlin. A stroll through the town between Alexanderplatz and the Großem Stern . (Guide to the geology of Berlin and Brandenburg; Vol. 6). 2nd edition. Self-published Geoscientists in Berlin and Brandenburg eV, Berlin 2006, ISBN 978-3-928651-12-7 . P. 115
  8. ^ Paolo Marchi et al .: Pietre di Liguria . Genova (Sagep Editrice) 1993, ISBN 88-7058-489-5 . P. 52