Nero Portoro Limestone
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Synonyms: Black Portoro, Nero Portoro, Port d'Or, Porte-Or, Portor, Portora, Portorro
Location: Nero Portoro limestone is quarried near Portovenere, Isola Palmaria, Provincia di La Spezia, Riviera Apennines, Liguria, Italy. Quarry production is quite small with varying block sizes, large blocks are not common.
Description: Nero Portoro Limestone is a black limestone (fault breccia) of the Jurassic period (Lias) with intensive yellow stylolitic veins and partly white, streaked veins. This stone internationally may be nominated as a marble but in the area of application of the European Standard this stone must be nominated as limestone.
A small sample of Nero Portoro limestone is not representative owing to a large variation in veining. Owing to this variation in veining swatch samples are usually of no help since all the blocks are extracted from the same quarry, selection is usually made either in the quarry or block stockyard for matching purposes. Nero Portoro limestone is ideal for interior use, it is not frost resistant and the polish is only constant inside.
The use of polished Nero Portoro limestone is not recommended for flooring tiles owing to high breakage rates and being very easy to scatch. It is quite common for Nero Portoro random slabs to be strengthened with glass fibre netting and resin and it must be stressed that it is a very expensive limestone!
Mineral Composition: Average by %:
Limestone: A sedimentary rock, mainly composed of mineral calcite. The primary source of the calcite is usually marine organisms, which settle out of the water column and are deposited on the ocean floors as pelagic ooze (but see lysocline for information on calcite dissolution). Secondary calcite may also be deposited in super-saturated meteoric waters, as is evidenced by the creation of stalagmites and stalactites.