THE WORLD’S MOST POPULAR MARBLES-Explanation

THE WORLD’S MOST POPULAR MARbLES

by Dr.Daniel Pivko
Dept. of Geology and Paleontology
Comenius University, Faculty of Natural Sciences,
bratislava, Slovakia
info@findstone.com

This article presents the hundred most-offered marbles (in the widest commercial sense). The marbles are described from a different point of view than usual viz. commercial name and type, country, petrographic type, geological age, water absorption, other commercial names, similar stones, and basis of name. Terms are defined first followed by tables of about 100 marbles in alphabetical order which is the main part. The idea for this article was from my experience and observation of the frustration of consumers and the trade in the process of selection, use, care and maintenance of marble as evident from the popular Expert Advice section of www.findstone.com . The data is based on my own research and revaluation of hundreds of web pages and some catalogues. Your questions, comments, corrections and additions are welcomed at info@findstone.com

Marbles in the widest commercial sense are softer natural stones than granites. Marbles are mostly polishable and they can be worked on by softer tools than for granites for cutting, shaping and polishing. The most important mineral is calcite. They are usually suitable for interior applications.

Many stone experts separate limestones, travertines and onyx marbles as individual groups from marbles.

Commercial		Scientific
Marble	Travertine	Travertine (high absorption)
	ONYX	ONYX MARbLE (low absorption)
	Limestone	Limestone, DOLOMITE (high absorption)
	Marble	Limestone, DOLOMITE (low absorption)
		MARbLE (low absorption)
		SERPENTINE MARbLE, SERPENTINITE (low absorption)

Marbles in a narrower commercial sense are softer natural stones than granites, while being more dense than limestones and travertines. Marbles take good polish and are used for more graded purposes (mainly polished facing and flooring).

Limestones in commercial sense are less dense, with higher water absorption, than marbles. They are not generally well polishable and are usually used for less graded purposes, as building stones, honed flooring.

Travertines in commercial sense are softer natural stones than granites, with large pores. They can take good polish and are used as building stones, flooring and facing.

Onyxes in commercial sense are softer natural stones than granites, typically with distinct colour bands. They can be translucent in thin slabs. Onyxes are well polishable and used for high graded purposes like marbles.

The boundary between marbles and limestones in a commercial meaning is different than the boundary between marbles and limestones in scientific meaning.

Marbles in scientific sense (true marbles) are metamorphosed limestones or dolomites. They are only one group of commercial marbles (see table).

Limestones in scientific sense (true limestones) are sedimentary rocks formed especially from biogenic fragments, less from precipitation from water.

Serpentine marbles are metamorphosed rocks created from special type of igneous rocks.

Dolomites, travertines and onyx marbles in scientific sense are sedimentary rocks formed by chemical precipitation.

Commercial marbles (in the widest sense) are medium hard and scratchable by a nail, knife or glass piece unlike granites. Depending on the calcite, dolomite and serpentine portions, the total Mohs Hardness for this group is from 3 to 4.

In commercial marbles, the larger the pore amount the lesser is the strength. In true marbles or in true limestones, the larger the grain size, the lower is the strength, and the greater is the brittleness, because mineral cleavage manifests more in larger grains.

The pattern of commercial marbles is very changeable unlike granites. The basic property of true limestones, onyx marbles and travertines is bedding – parallel arrangement of particles (manifested in grain size, colour or shape). Especially limestones and some true marbles can be cut by veins of different directions. Many limestones contain visible fossil remnants. True marbles and onyx marbles are composed of visible calcite (aragonite, dolomite) crystals like granulated sugar. On the contrary, limestones and travertines are without markable calcite crystals or grains. Only some parts as fossils or veins can be with crystals. True marbles have grainy, cloudy, streaky, banded, wavy, brecciated (broken pieces) patterns.

Commercial marbles (except serpentinites) are affected by common organic acids such as a lemon acid and vinegar, contrary to granites. They react more with salt acid (HCl) and other common acids. Commercial marbles are not suitable for external use because acid rains (and any rain in less portion) contains acids which decay stones. Water absorption of limestones is larger than common granites, therefore they are more easily destroyed by frost.

Explanation of every column in the table is given below. Sample images are in the Stone Album of www.findstone.com but other images can be found elsewhere.

In the first column, the most frequently used or the most suitable names are presented alphabetically, further country and its part, and commercial type as a marble, limestone, travertine or onyx.

COLOURS

In the column typical colours are presented according to their importance. Some variations are possible.

PETROGRAPHIC TYPE

SEDIMENTARY ROCKS. Rocks on the earth`s surface are exposed to weathering. They are fragmented and chemically changed. Formed fragments and solutions are most often transported by rivers to the sea.
-Clastic sediments are accumulated from rock fragments, e.g. gravel, sand or clay.
- Chemical sediments are formed by chemical precipitation - as some limestones or salts.
-Organic sediments are created from accumulation of animal or plant bodies, e.g. coquina or peat. Most sediments are deposited in the shape of beds, which are later compacted and cemented in to coherent sedimentary rocks by pressure of overlying beds and other processes (lithification). Gravel was changed to conglomerate, sand to sandstone, clay to shale.

A large part of commercial marbles are limestones formed especially from inorganic remnants of organisms. Some of them were created by precipitation from fresh water (travertines, onyxes) or marine water (oolitic limestones) or accumulation of limestone fragments (carbonate breccias). Some limestones were chemically altered to dolomites.

Limestones are mostly of marine origin. They are composed of calcite (calcium carbonate) or less of aragonite (other modification of calcium carbonate).

During lithification, when pressure and temperature got raised under overlying beds, some calcite grains and fossils were dissolved and later joined by calcium carbonate cement. Pore spaces were diminished and strength was increased.

In some limestones, accumulations of siliceous materials – chert nodules or layers are created during lithification. During pressure and temperature action, zig-zag lines (stylolites) are formed in some limestones caused by uneven dissolution (e.g. FILETTO ROSSO).

An important factor for compact limestone origin is time and higher temperature and pressure during a mountain formation. Folded and deformed limestones are usually more compacted than undeformed ones. During deformation, many limestones were broken to pieces and then fissures among them were filled by calcite veinlets and veins of different orientation (e.g. ROJO CORALITO).

Limestones which were uplifted close to earth`s surface are affected by water, which dissolves limestone (and also marble) beds and caverns and cavities are formed. Cherts, stylolites and cavities are defects during limestone and marble working.

between particles are minute pore spaces that can be filled in different portion by cement.

The following limestone types can be separated:

· fossiliferous (bioclastic, skeletal, shelly) limestones are composed from fossils or their parts. These limestones contain various shells and skeletons, like shells, clams, mussels (ROJO ALICANTE), special shells – rudists (AURISINA), algae (JURA MARMOR), algal oncoids (bOTTICINO), crinoids - sea lilies (CREMA MARFIL), and large single-celled organisms - foraminifers (CHIAMPO with nummulites)

· micritic limestones (microcrystaline limestones) are made of mud size calcite particles of chemogenic or biogenic origin and microscopic skeletons of foraminifers (ROSA PERLINO)

· nodular limestones as a type of micritic limestones are composed of rounded nodules to some cm formed probably during solid rock formation (ROSSO VERONA)

· stromatolitic limestones – banded limestones created especially by blue-green algae activity (SERPEGGIANTE)

· limestone breccias (carbonate breccias) are rocks of cemented angular fragments of older limestones, e.g. destroyed parts of coral reefs (bRECCIA PERNICE).

Dolomites

Dolomites (dolostones) are composed of dolomite mineral domination. Dolomites were formed when Mg-rich solutions influenced calcareous sediments. This process occurs during special conditions inside very shallow marine sediments in hot dry climates.

Dolomites are usually harder, heavier, more brittle and appeared more fractured than limestones (e. g. dolomite breccias – MARRON EMPERADOR). There are transitions from limestone to dolomite:

They are fresh water limestones formed by precipitation of calcium carbonate (calcite, aragonite) from hot of cold mineral springs. Pores come from carbon dioxide escaping or from destroyed algal or plant bodies. Travertines can be partly used like external stones because their large pores are not destroyed by frost. athough large pores are disadvantageous because of its difficults maintenance.

They are created by calcite or aragonite precipitation especially in caves. Onyx marbles are compact-usually banded rocks or sometimes translucent.

METAMORPHIC ROCKS were formed by the recrystalization of sedimentary or magmatic rocks under the earth‘s surface during raised pressure and temperature conditions. Metamorphism follows lithification in higher temperature and pressure. Transition between lithification and metamorphism is in the 100 – 200 ºC span. Appearance of new minerals is substantcial feature of metamorphism.

True marbles, serpentine marbles and serpentinites are commercial marbles of the metamorphic origin.

Marbles are metamorphosed limestones or dolomites. During metamorphism when pressure and temperature are raised, calcite crystals of limestones are further reduced in number and increase in size. Crystals interlock closely to give increased strength and decreased pore spaces. Calcite marbles (or simply marbles) are formed from limestones, while dolomite marbles from dolomites. Some new minerals appeared in marbles created from admixtures in limestones. Marbles have a granular appearance from about 0.1 to some milimeters crystals.

The larger the crystals, the less the strength, & more the brittleness in marbles. Dolomite marbles are usually harder, heavier, more brittle, less polishable and have higher water absorption, than limestone marbles. Dolomite mineral is more resistant against acids than calcite.

They are green metamorphic rocks composed of serpentine (Mg silicate) domination. They are formed by metamorphism of ultrabasic igneous rocks (e.g. peridotites).

They are green metamorphic rocks composed of calcite and serpentine (some are reddish with hematite admixture). These mixed rocks were created during mountain building processes like the serpentinites.

The age of the stone is determined in the table by the geological time unit when the stone was created by the geological process. In some cases the older the stone the larger the strength, and the smaller the water absorption Original rocks for metamorphic rock can be formed much earlier than where metamorphism changed the rocks. For instance, limestones can be created in Paleozoic, but they were metamorphosed in Terciery.

Terciery

Mesozoic

Paleozoic

WATER AbSORPTION bY WEIGHT

The percentage of water absorption into stone by weight is determined by the ratio of absorbed water weight and stone weight. Values have been re-evaluated from many sources and they are rounded off. Values in brackets are less reliable because of small amount of data or estimation according to similar stones. The stage of limestone compactness is presented .

OTHER NAMES AND VARIETIES

Lless used or less suitable names and varieties are presented. Many are not quite correct because the word order is reversed or they are incorrect because of wrong spelling or have been mistaken for another stone.

This column can help stone specialists and customers to find similar stones. A stone is similar to another stone by its appearance: colour(s), grain size and particle pattern (arrangement). A stone is partially similar to another one, when some feature is not such evident. In this column, there are also additional stones not covered in the Commercial Name and Other Names columns. Use "Ctrl+F" or "Find in Page" feature of your computer to find your stone in the Other Names or Similar Stones columns.

Commercial names have different origins. The majority of names are derived from a geographic area or colour. The geographic site could be the quarry place, nearby town or the state. The colour is described in English, Italian, Spanish or other languages. Some stones have their names according to colours of precious stones, plants or animals.

Aragonite – mineral: calcium carbonate CaCO₃, crystal structure other than calcite

bedding - parallel arrangement of particles manifested in grain size, colour or shape

Calcite – mineral: calcium carbonate CaCO₃, crystal structure other than aragonite

Cherts – siliceous sedimentary rocks: siliceous layers or nodules inside limestones

Chlorites – group of minerals: silicate similar to micas with aluminium, magnesium and iron

Conglomerate - solid sedimentary rock composed from rounded particles over 2 milimeters

Fossils – remnants of shells, skeletons or tests of organisms; also impressions of organisms

Igneous rocks - or magmatic rock are formed by crystalization from magma (melt)

Lithification - process by which unconsolidated rock-forming materials are converted into consolidated or coherent state. Compaction - pressure decreases pore space between particles. Cementation - deposition of minerals in pores.

Metamorphic (metamorphosed) rocks - sedimentary or igneous (magmatic) rocks that were altered by heat and/or pressure

Mohs Hardness - determined according to a relative scale which consists of ten minerals arranged in order of their increasing hardness

Nodules – oval (up to some cm) particles formed during sedimentation or lithification

Oncoids – oval coated-grains of calcium carbonate formed by algae of foraminifera

precipitation - chemical or biogenic process where solid material is appeared from solution

Sedimentary rocks - formed from deposition of rock fragments and fossil remnants, or precipitation from solutions

Stylolites – zig-zag lines which are remnants after uneven dissolution of limestones; contain clay minerals and ferric oxides and hydrates

Translucent – light passes through the mineral but the object viewed is not clearly outlined

Veins, veinlets – areas of various directions which cross rock (like lines on stone slabs); fissures formed mainly by rock deformation filled by calcite

Weathering – processes of mechanical disintegration and chemical decomposition of surface rocks

Copyright Dr. Daniel Pivko

www.findstone.com is a natural global marketplace to buy or sell stones.