Formation of Limestone to form Marble
Process in BriefThe geology regarding the formation of limestone to form marble is complex, however, very specific chemicals and organisms influence the mineral composition. Calcium carbonate is the primary chemical compound in crystalline forms (polymorphs) calcite and much less prominently aragonite and vaterite depending upon magnesium content. Sediments in the oceans are primarily skeletal remains of organisms and fragments of eroded rock, the purity of Limestone and Marble depends on the content of these factors. As layers of sediment are compressed they go through a process of lithification and diagenesis where physical and chemical changes convert sediments into fine grained sedimentary rocks, including Limestone. The conditions required for limestone tranformation (metamorphism), is high pressure and heat. Deep within earth there is a barrier where pressure and heat increases called the 'geothermal gradient', below this, rocks of all forms will return to the start of the rock cycle as magma.
Chemicals and Organisms
Magnesium (Mg) Influences Mineral SolubilityA large factor that influences mineral composition during Earths changes and climate periods is Magnesium. It plays an important role in enzyme reactions of living organisms, including muscles, nerves and regulating pressure. Magnesium also increases the solubility of minerals and absorption in living organisms.
Climate VariationsIt can therefore be deducted that geological and climate variations of magnesium instigate marine organism migrations over large periods of time, changing mineral solid precipitates to vary in composition. It is evident that waters that created pure calcium carbonate (CaCO3) 'chalk limestone' were not marine ecosystems during the period of formation, but either freshwater or acidic systems with a higher level of 'Carbon dioxide (CO2)'. Therefore, less abundance of organisms that require and produce magnesium.
Seawater Source of MagnesiumMarine ecosystems are distinguished by waters that have a high salt content 'sodium chloride (NaCl)' and are currently the largest aquatic ecosystems on earth. The source of magnesium in seawater that is essential for marine organisms to thrive most likely comes from the erosion of high magnesium mafic igneous rocks (dark colouration) that consitute oceanic crust. Upwelling mantle along the mid ocean ridges produces mafic igneous rock through partial melt, and form the tectonic plate boundaries, swelling outwardly as if the earth is expanding. The chemical reactions during these events provide elements and minerals that are essential for marine environment life to thrive.
Calcium Carbonate (CaCO3)1x Calcium, 1x Carbon and 3x Oxygen Atoms form the soluble Chemical Compund Calcium Carbonate (CaCO3). Calcium carbonate comprises approx 4% of the earth's crust and is found worldwide as the minerals calcite and aragonite. Calcium Carbonate constitutes approximately 20% of the worlds sedimentary rocks and most commonly known to form as Chalk, limestone, marble, travertine, and tufa.
Calcium Carbonate ContributorsMarine waters are rich in calcium carbonate and the main contributors to this is marine organism excretions, fecal matter and remains. Most of these organisms are typical of shallow water environments where sunlight and filterable food are more abundant. Calcium carbonate is the main component of shells, seashells, skeletal structures, cell walls and spicules of marine organisms such as molluscs, Echinoderms, Microscopic Organisms, Algae and Filter feeders. When these organism die, the remains settle and either broken down by ocean currents or compressed by the pressure of overlaying sediment over long periods of time.
Carbonate Minerals and Crystals
Calcite, Aragnoite and VateriteSignificant constituents of the calcium cycle are the crystal forms of calcium carbonate as polymorphs 'calcite', 'aragonite' and 'Vaterite'. The mineral calcite is important for biological mechanisms and life as we know it, its trigonal crystal structure is more stable than its more complex counterparts Aragonite (orthorhombic) and vaterite (hexagonal). Magnesium adffects the stability of the crystal structure, the higher the magnesium ions present the more likely Calcite will form in place of vaterite and aragonite. The introduction of magnesium rich waters will revert the crystalline forms vaterite and aragonite to the more stable trigonal crystal, calcite.
Calcium SolubilityCalcium Carbonate is a soluble mineral, environmental changes increases the solubility of calcite. Small cavities and channels called 'vugs' can form in exisiting limestone when calcite is dissolved. Crystal types calcite, quartz, dolomite and barite among others can line these Vugs, formed from precipitates during the process of diagenesis.
Primary Mineral CalciteBased on geographic locations and mineral composition of exisiting calcium carbonate deposits worldwide it is suggested that through chemical reaction the primary mineral solid (precipitate) formed in marine waters was the mineral 'calcite' that was low in magnesium content. Arroganite and high magnesium calcite are more prominent in more recent deposits. The conditions that change the mineral content of calcium carbonate depend wholly on climate cycles and geographic changes affecting the organisms that reside in the waters during those periods.
Three Crystalline Polymorphs of Calcium Carbonate
Trigonal Crystal 'Calcite'Calcite is the Primary mineral in Marble and belonging to the most stable Trigonal Crystal system. It is the main component of eggshells, snail shells, seashells and pearls. High-magnesium calcite retains the calcite mineral structure
Orthorhombic Crystal 'Aragonite'Frequently forms in near-surface environments at ambient temperatures and does not usually contain significant magnesium. Forms as columnar or fibrous or as branching helictitic forms called flos-ferri ("flowers of iron")
Hexagonal Crystal 'Vaterite'As an unstable polymorph it is rarely found and is most likely to be encountered as the mineral forming the inner shell of mollusks. Pure vaterite has been discovered on the leaves of alpine species saxifraga sempervivum
Deposition of Sediment
What is Sediment made from?Sediments are made up of grains formed primarily from the remains of marine organisms and microscopic animals leaving behind skeletal fragments and detritis that have sedimented to the bottom of continental shelves. This makes sediment in the oceans the largest source of calcium carbonate. Another contributing factor of sediment is fragments of rock through erosion ashore or from the seafloor. The build up of sediment (deposition) goes through a process of diagenesis in which is the sediment undergoes physical and chemical changes and/or Lithification, converting freshly deposited grains of sediment in to rock. Variable amounts of silica in the form of chert or siliceous skeletal fragments is also common in sediments.
Grain TypesThe terms 'Allochems' and 'orthochemical' describes types of carbonate rock grains found in sedimentary rocks, varying in size from microscopic to visible particles. Allochems are fragments or grains that have formed prior to settling as a sediment. Orthochemical are grains that form on location through chemical precipitation during the cementing process, and generally consist of micrite or sparite. The larger grains are often seen in limestone and sometimes in Marble.
BioclastsA majority of grains are skeletal fragments of marine organisms, invertabrates and their secretions with varying levels of magnesium.
Ooids / OolithsGrains of less than 2mm with layers of calcite or aragonite on a central quartz grain or on a carbonate mineral fragment.
PisolithsSimilar to ooids but irregular in shape and larger than 2mm in diameter, also known to form subaerial (open air or on the earth's surface)
OncolithsGrains of less than 2mm with radial layers of calcite or aragonite on a carbonate mineral fragment or quartz grain.
Peloidsstructureless grains of microcrystalline carbonate - formation is unknown and only speculative.
LimeclastsEroded fragments of limestone or partially lithified sediments from within (intraclasts) or outside (extraclasts) the depositional area.
Physical and Chemical Changes in SedimentLithification and diagenesis processes often work in tandem and according to the rate of the forming sediment. Upper layers of sediment will produce several different grain types that eventually get cemented together by precipitates of chemical reactions.
LithificationLithification is a process whereby freshly deposited loose grains of sediment are rearranged under pressure, driving out mineral rich fluids during compaction. Reactions between the dissolved minerals in the ejected fluids may form new minerals. Minerals from under water currents can also be combined, and redistributed into nodules and concretions as cementation.
DiagenesisThe Process of Diagenesis is the physical and chemical changes in sediments after it has settled down (deposition) include and according to conditions: adsorption, dissolution, precipitation, microbial activity, and compaction. sediments are compacted and porosity decreases (except dissolution of minerals and dolomitization) as they are buried beneath successive layers of sediment deposition and cemented by minerals that precipitate from solution (precipitation). As the compacted sediment is carried deeper by further deposition above, its organic content is progressively transformed through decomposition into Kerogen (insoluble organic matter).
Fine Grained Sedimentary RocksThe 2 Primary types of carbonate mineral sedimentary rocks are limestone and dolomite. Chalk and carbonate mud also contain a high percentage of carbonate minerals and maybe formed through abrasion and erosion of carbonate rocks and sediments.
Dolomite (Dolostone)Magnesium rich waters present at the time sediment undergoes lithification or diagenesis, recrystallisation (dolomitization) can occur where a proportionate amount of calcite ions are replaced by magnesium ions to form Dolomite. The recrystallisation process dissolves the calcite minerals and the resulting chemical reaction with the magnesium and combined with temperature exceeding 25 degrees C, magnesium quartz will form. This fine-grained sedimentary carbonate rock has an appearance varying from banding to pockets of large crystals and has higher resistance and is less soluble than limestone formed with calcite due to its larger magnesium quartz crystal content.
ChalkPurported to have formed in the Cretaceous, Chalk, a fine grained sedimentary rock that is classified as a soft, porous form of limestone composed mainly of the mineral calcite. lack of erosion from nearby rocks provides some explanation to the high purity of chalk. A calm, mild climate during this period would of likely enticed mostly microscopic organisms that thrive in low magnesium conditions. Most likely, the lithification and diagenesis processes differ in that the chemical soup from decaying microscopic organisms, mainly calcite, is a result of a period of rising ocean levels. Further increasing compaction rate accompanied by mass population or migration.
Carbonate Mud (Micrite)Carbonate mud (Microcrystalline Calcite 'Micrite') constitutes 50% of all fine grained siliclastic sedimentary rocks, and are formed generally by erosion. Micrite consists of individual crystals of less than 5 microns. The micrite crystals are primarily of calcite and aragonite. Recrystallization of the micrite crystals produces microspar with grains of over 5 microns. Presumed to be formed through precipitates from seawater, algae secretions or produced by abrasion or the dispersing of skeletal remains. It seems likely that the abrasion of forming sediments through higher energy currents will set down fragments as a carbonate matrix in sheltered locations prior to recrystallization. slate is derived from a shale which is the finest grained metamorphic rock. Carbonate mud or Calcilutite contains a high content of carbonate minerals of Calcite and aragonite.
LimestoneSedimentary Rock Limestone is primarily made from calcite (Stable Crystal form of Calcium Carbonate CaCO3) and various rock fragments.
Limestone ColoursThe colours in Limestone depends on the minerals it is made from, as limestone is primarily made from calcite and skeletal fossils, white to grey is most common. Minerals making approx 5-10% by average such as quartz, clay and magnesium will give a grey colouration. Trace minerals in limestone will oxidise through weathering mostly through rain and draining water. Yellow and reds are caused by traces of Iron and manganese, organic matter will darken the limestone and can be almost black.
HardnessLimestone as a sedimentary rock is relatively soft with a hardness of three on the mohs scale, however, it has a crushing strength by over four times that of today's concrete. It comes as no surprise then that our more evolved ancestors avoided concrete!
Weathering and Acid DegradationThe calcite crystals in limestone are partially soluble, and is evident in many stark erosional landforms seen worldwide from rain and draining water. The minerals in limestone cause the different colours exhibited during weathering and acid degradation. Acid rain though dubbed as purely man made, is a natural process, though we undoubtedly contribute with environmentally unfriendly processes. Naturally, rain mixes with carbon dioxide, nitrous oxide and sulfuric dioxide in the atmosphere and also the draining water mixes with acids from decaying organic matter. The draining water and sometimes acidic water (acid degradation) will over long periods of time dissolve the calcium carbonate peeling away to show the sediment layers and enlarge cracks to form karst lansdscapes, caves and gorges etc.
Karst Landscapes (Limestone Bedrock)
As limestone slowly erodes, years of weathering forms Karst landscapes that consits of underground streams, sinkholes and caves. Half a mile north of the village of Malham, in the Yorkshire Dales National Park, a large limestone formation 'Malham Cove' features a curved cliff and karst platform. it is presumed to have been formed by glacier meltwater at the end of the last ice age.
Dissolved calcium bicarbonate in run off water from limestone can form stalactites as it drips from the ceiling of a cave. Some of the calcium bicarbonate precipitates back into limestone as it comes into contact with the air. Mother Shipton's Cave in Knaresborough, North Yorkshire, has what they call a 'petrifying well', where limestone water run off can coat a small teddy with limestone in as little a few months.
Limestone UsesLimestone is used widely for a variety of purposes and include construction, agricultural, smelting, desulfurisation, glass making and calcium supplements. As a major and widely used industrial raw material and its viability economically, high demand classifies it as a critical raw material. It must also be noted that the processing of limestone for all consumption is a very large contributing factor to Co2 emissions.
Limestone InfrastructureArchitecture, escpecially megalithic and tartarian architecture, which still stands today and outlast our modern post 19 century buildings. Town halls, train stations, banks, libraries, churches, castles and notable buildings of our modern infrastructure were generally made totally or with a large quantity of limestone. Today's architecture uses powdered limestone and clay heated to form cement which is the main ingredient in mortar and concrete.
Calcium Carbonate AdditivesCalcium Carbonate is widely used as an additive. In foods, calcium carbonate is added as a source of calcium, acid reducer, white food colouring, caking agent and to strengthen dough. The list of uses for calcium is almost endless and is also fed to livestock as a supplement, added to our tap water and used within most pharmaceutical products! The calcium carbonate additives are in the form of limestone dust which has been proven to cause mild respiratory issues, be a skin irritant and cause sillicosis or cancer. Excessive consumption can cause hypercalcemia and disgestive issues.
Limestone Transformation into MarbleModern day geologist and scientists according to their academic status, will provide a complex explanation for the processes earlier described in the formation of limestone, with an equally more complex theory for the transformation of limestone into marble. Taking into considering the classical elements and processses involved will help to understand how the rock cycle works, and I feel that this is important to cover this in brief before jumping straight to metamorphosis of limestone in to marble.
Influencing Classical Elements of ChangeThe change in states of minerals is akin to the classical elements influencing change. To consider the classical elements 'earth', 'fire', 'air' and 'water' and fifth element 'aether' is to understand the basic process of cycles and changes that we see in our physical world. Older and labelled as less advanced, past civilisations used these terms to explain the basics of our physical world with aether also being described as a natural phenomena of many different names. In respect of the Rock Cycle, various attributes contribute to the breaking down and formation of rocks of all types and directly correspond to these elements. These elements almost always work in combination with each other and include the processes required for life and its cycle.
The Rock CycleA concept that explains the changing state of rocks in relation to its exposure to the elements over geological time. The three major rocks types will over time transform and recycle in an ongoing process called the rock cycle. All aspects of the elements will have an impact on the building and breaking down of rocks, including weathering and the movement of the earth through what we see as volcanos and earthquakes etc. These events influence the chemical and biological (aether) changes required to alchemically transform one into another.
Platonic SolidsPlato and possibly Pythagoras designated each element with a geometric shape known as the platonic solids, corresponding to the basic buidling blocks of our physical reality. The shapes were chosen according to their movability. Corealations are extensive and include colour, frequency, mathematics, chakras, Metatron Cube even substances under pressure will take on particular geometric properties. Despite fundamental and so many obvious corealations, the classical elements are not supported by modern science and a complex 'atomic theory' is used, removing aether.
FireHeat from ambient to extremely hot conditions. A method of transmutation in combination with Earth and other elements. Attributes: Thawing, Crystallization, Gassing, Melting, Convection
Platonic Solid: Tetrahedron - 4 faces, Plasma
Dual - Inverted Tetrahedron
EarthThe platform that we consider the physical world as we see it today. All the particles and elements that make up everything we see. Attributes: Container, Medium, Order, Geometric matrix
Platonic Solid: Cube - 6 faces, Solid
Dual - Octahedron
AirAtmospheric pressure providing a space for above and below and a medium for transportation of Earth and other elements. Attributes: Oxidization, Wind, Abrasion, Erosion.
Platonic Solid: Octahedron - 8 faces, Gas
Dual - Cube
AetherThe unseen electrical transfer and frequency response in chemical reactions and contact between Earth and other elements. ttributes: Charge, Frequency and Vibration (Cycles of time), Magnestism (attract and repel)
Platonic Solid: Dodecahedron - 12 faces, Universe
Dual - Icosahedron
WaterWater is the carrier of information (minerals), four different states enter in to Earth to provide minerals and chemicals required for change. Attributes: Freezing, Dissolving, Evaporation, Abrasion / Erosion, Absorption, Precipitation
Platonic Solid: Icosahedron - 20 faces, Liquid
Dual - Dodecahedron
Metamorphism - Conditions Required for ChangeConditions required for metamorphism to change sedimentray rock into Marble involve several factors, all of which involve enough pressure and heat to cause a partial melt or extreme heating of the parent rock (protolith). Too much heat or pressure and the rock will fully melt and return to magma restarting its journey on the rock cycle. The protolith can be igneous, sedimentary or an already metamorphosed rock. Metamorphism can be caused by compression from overlying rock, tectonic stress, extreme heating from magma, or alteration by fluids. The geothermal gradient is a term that describes the increase in temperature the deeper you go inside the earth, if sediment layers are deep enough they will experience temperatures high enough for metamorphism. Tectonic movements can also force rocks into the earth deep within the geothermal gradient. Stress and pressure can be exerted on the rock in several ways, the stresses that the rock has undergone can be seen in the formations in most rocky outcrops and mountainous regions.
Contact MetamorphismOccurs when heat from magma at an igneous intrusion comes in contact with a body of rock (aureole). fluids and gasses from the magma and its surrounding environment begin to intract with the existing minerals. Contact metamorphism may contribute to the intense crystal bandings that are found in mountains.
Regional MetamorphismAffecting a large area in mountainous regions, extreme pressure or compression (differential stress) from the subduction and uplifting of continental crust. Most likely to cause Lithostatic Pressure, where source is from the weight of rocks above that causes equal pressure exerted from all directions and uniformly is Lithostatic pressure.
Dynamic MetamorphismSimilar to regional metamorphism, however, the huge sudden or constant forces of heat and pressure will cause the rocks to partially melt enabling them to be bent, folded or sheared. Uneven pressure (differential) either stretches as it is being compressed and pushes in a single direction or sheered from two opposing forces and can lead to foliation which is seen in rocks with flat layers.
RecrystallizationRecrystallization is a process that occurs When sedimentary rocks limestone, chalk and dolomite are exposed to high temperatures and pressures. Often as a result of crustal movements, they go through a process of metamorphism in which the calcite crystals in the rock recrystalise. The recrystallization of calcite in these conditions makes them grow larger, forming a dense and interlocking lattice of equigranular calcite crystals. The original sedimentatry structures (grains and micro skeletal fossils) in limestone are dissipated by crystal expansion, changing the texture and appearance. Limestone at the location of shifting continental plates undergo 'contact metamorphism', where hot magma sparks intense crystal growth. Other minerals such as clay and complex silicate structures will also metamorphose to produce micas, and gem minerals.
The mineral rich fluids (fluid phase), locked in the protolith play a key role in the chemical reactions that transform the mineral content and texture. This may even transform the protolith so that its original state is difficult to determine. The fluids will determine the chemical reactions that take place, and the rate of mineral crystal growth and deformation. Ocean water can penetrate cracked oceanic crusts and faults and circulate crustal areas, including magma. Transporting hot hydrothermal fluids loaded with minerals which are necessary for chemical reactions, and may even cause metamorphism (hydrothermal metamorphism).
Marble ColoursPure white marble has a crystalline and sugary appearance and formed from very pure and low in silicate limestone or dolomite (low magnesium interruption). Other minerals including quartz, pyrite, graphite, iron oxides and clay incorporated with Calcite during metamorphism is what gives marble its wide varitey of colours, veins and swirls. Marble that contains impurities such as clay minerals, iron oxides can be bluish, gray, pink and yellow. Green, brown coloration is often due magnesium-rich limestone or dolomite forming the mineral serpentine.
Mistaken for MarbleDense, massive limestone is sometimes described as "marble", for example, the famous Portoro "marble" of Italy is actually a dense black limestone. As quartzite has similar appearances, some marbles are mistaken as quartzite and can lead to very dissapointing results as marble is much softer that quartzite. Because travertine, serpentine and breccia are also carbonate based sedimentary rocks that can be brought to a high polish, they are occasionally mistaken as marble.
Marble DepositsMillions of tonnes of marble are mined and quarried every year from deposits hundreds of feet thick, mainly in mountainous regions. Even though marble is Found all over the world, Italy, China, Spain, and India account for 50% of its production. Ireland’s wild Atlantic coast has an exclusive and rare marble deposit 'Connemara marble'. Unique and striking with green of many hues in varying layers and patterns.
Construction and SculptureMarble is crushed or cut into blocks or slabs as dimension stone and used for a variety of purposes in the construction industry. In its crushed form, its used as aggregate, or in the block and slab form used for monuments, sculptures and decor such as worktops, floor tiles, and windowsills. Carrara Marble from Carrara in Italy is a famous marble and was used by Michelangelo, Donatello, and Canova for their masterpiece sculptures.