The Italian Metamorphic Marly Limestones: Polombino, Moresco, Jasperine and Nephritic
Information about the Italian Metamorphic Marly Limestone Rocks
By Marco Patruzzelli, PhD, Geologist, November, 2019
(This article was adapted from the Italian IBS “Italian Bonsai and Suiseki Instructors Manual” in cooperation with VSANA.)
If suiseki lovers image an Italian stone, they think about a Polombino Ligurian stone. But in Italy, there are many other calcareous stone types that are similar to Chinese stones or fantastic volcanic and flint stones with patterns and bright colors. What is a Palombino stone type from a geologist’s viewpoint? Three fundamental questions must be asked. First, which stones should really be called Palombino? Second, what is the origin of this hard and lucent stone? And third, is it correct to say that this type of stone is only found in northwestern Italy?
Schematic of mountain chain showing where ophiolitic stones and metamorphic marly limestones occur.
Knowing a stone is fundamental to understanding how to treat it during the collecting and cleaning process so as to create the optimal patina needed to create a great exhibit. A bonsai collector always knows the right taxonomic name and the botanical features of the plants he is maintaining. This trait does not always apply to stone lovers who use different nomenclatures for stones from time to time. In fact, the scientific name of the stone is considered to be a secondary feature. The historical determination or the poetic name of the stones is often preferred. This is the case of the Palombino; some types of stones have “petrological names” used in local tradition or for commercial use and this parallel determination does not correspond to the specific geological name of the stone.
The problem becomes apparent when an Italian suiseki aficionado tries to translate the petrological name in another language, cannot find a corresponding translation, ends up thinking that the “Palombino” is only found in Italy. In geological terms, Palombino is in fact Metamorphic Marly Limestone. This stone is a calcareous stone that is not pure limestone but contains less than 40% silicate minerals. These are metamorphic rocks found all over the world, typically formed near the basement of a mountain chain. This means that this stone was subject to heat and pressure through geological mechanisms that transformed some of the minerals and structures that characterize the stone. The limestone originated at the bottom of the sea, but in the process of becoming part of the center of a mountain chain mixed with other mineral types and stones to form a new stone. As a result, we have different varieties of Metamorphic Marly Limestone depending upon the origin of the silicate materials that are part of this rock. Thus, a Palombino rock is a Marly Limestone rock, but not all Marly Limestone rocks can be called Palombino.
Example of what suiseki lovers mean when speaking of Palombino stone. (photo by Luciana Queirolo).
The stones coming from the center of the ancient mountains of all over the world are called ophiolitic stones or serpentine stones. Ophiolitic is derived from the Latin word ophios meaning snake; while serpentine is derived from the Greek word serpens also meaning snake. These stone have a texture and coloration similar to the skin of a snake. The ophiolitic stone family contains precious minerals as garnet, Spinel, jade or jasper and dangerous ones such as asbestos! The combination of minerals and formation environments gives great variability to this family of rocks. The classification system here reportedly derives from the stone merchant international nomenclature and divides the types of Metamorphic Marly Limestone by color, hardness, and fracture system. On the other hand, geologists classify Metamorphic Marly Limestones all in the same “species” because all of them have the same mineralogical compounds and change of color is considered to be irrelevant.
The definition of Palombino as given in the Italian National Geological Survey Stone Catalog for commercial finality is: “Ornamental metamorphic stone characterized by a uniform light grey or ivory color that sometimes can assume yellowish colorations and dark grey or brown irregular and millimeter wide irregular veins.” Its name comes from the affinity to the feathers of some varieties of pigeons plumage (“colombino” in Italian) or from the affinity with the skin of the shark Mustelus mustelus
which is also called (“Palombo” in Italian). The stone gives the name to the type location where this stone type was first found. Mount Polombo is located in central Italy and not in Liguria.
In the geological sciences, it is important that any determination of color must be based upon a freshly cleaned surface and not on a surface that has an altered or artificially created patina. The color variations of the different types of Italian Metamorphic Marly Limestones is caused by an approximate value of 30% of silica in the limestone matrix. Being a metamorphic rock, no fossils or stratification can be seen in the single stone piece. What is the true name and color of all the varieties of Metamorphic Marly Limestone?
The classic mountain Palombino stone with white calcite veins. (Photo by Sergio Bassi).
First is the light grey variety that is called “Palombino”. It is derived from a sedimentary limestone with clear white silica impurities and results in the most tender and delicate variety when cleaned.
A landscape stone of the Moresco type, note the deformed veins (photo by Tom Elias).
The second variety is the dark grey or black type that assumes the name “Moresco.” This name side rived from the word “moro” that means dark skin in ancient Italian. It contains carbon impurities originating from the anoxic decomposition of organic matter. The Moresco type is a little harder than the Palombino stone.
Landscape stone with typical grey veins of green Nephritic variety (photo by Carlo Maria Galli).
The third type is the “Nephritic” which is green colored. This type of ancient limestone contains silica coming from the nephrite mineral formed in volcanic intrusions in the limestone. Nephritic limestone results in a harder stone than the either the Palombino or Moresco types. Nephritic limestone is more fragile and subject to breaking. Nephrite is one form of jade, although the Italian jade is not very pure and is not of jewelry quality.
Landscape stone with great red Jasper inclusions and rusty patina (photo by Claudio Villa)
The fourth is the “Jasper variety” containing Jasper silica and iron oxides acquired during oxidation of fossil remains before the metamorphic processes. The Jasper varieties are the hardest and after cleaning can sparkle.
Palombino arch stone with typical crossed fracture giving snake skin appearance in serpentine rocks (photo by Agostino Pretolani).
(top) Combination of two types of Palombino—Nephritic mixed with Jasper—often appears in nature in primary deposits (photo by Agostino Pretolani); (bottom) Great calcite vein in a waterfall stone eroded in a secondary river deposit (photo by Vito Divenere).
Large eroded boulder coming from a secondary deposit with more calcite than dark matrix (Photo by Marco Petruzzelli).
The conditions that result in the formation of Metamorphic Marly Limestone are not restricted to Italy but occur in different regions of the Earth’s ancient sea floors were metamorphized into mountain chains. In Italy, this occurred in the western Alps, while in central Italy this occurs in middle portion of the Apennines and in the Basilicata and Calabria territories where the most ancient part of the Apennine chain is exposed.
I see many Jasper and Nephrite stones on the VSANA web site (
www.vsana.org ) or in some U.S. of collections or stone shops. The Metamorphic Marly Limestone may be difficult to identify specifically because the surface patina has been strongly altered by neighboring deposits of silicates or other colored minerals. The aspect of these stones changes depending on whether they are found in a primary deposit or in a secondary one. The primary deposit is placed in a rock strata set coming from an outcrop that shows a transition between the hard stone strata and the softer siliceous sediments. In this case the stone is covered by a strong patina from adjacent materials and must be strongly cleaned to reveal the true color. A secondary deposit could be a river or a slope where the weathering effects can alter the patina by removing some or all of the mineral deposits on the surface the stone. This can also result in the stone breaking or the polishing effects can alter the original stone.
The greatest characteristic of this particular type of limestone is that it is shiny and clear in shape. In my opinion, the best examples are not the shiny ones but the ones that still have a thin original patina on the surface. The patinas in Palombino and Moresco result in a yellow or brown color. The Nephritic results in a white color while the Jasperine stone are light grey and rusty. Playing with the colors of the patina and the cultivation of this stone under weathering dissolves the shiny and uniform skin of some of these stones.
The four types of Metamorphic Marly limestone are all collected and used in stone exhibitions in Italy. The distinction between them is based upon color and surface patina that is, in turn, determined by the mineral composition of each type of limestones. As the different types of Italian limestone rocks continue to gain prominence among stone lovers worldwide, stone lovers will begin to distinguish and appreciate these beautiful stones.
