Weathering may have a degrading effect on the appearance and structural soundness of limestone. Factors include rain, snow, temperature, wind and atmospheric pollutants.
Generally these factors act in combination with one another or with other agents of deterioration. Rainwater, especially in combination with atmospheric gases often resulting in acid rain can result in dissolution of the limestone, causing higher levels of salt movement within the stone structure.
Temperature can effect rates of deterioration and in larger stones movement of the pieces, as well as patterns of salt migration within the stone. Most of the natural or inherent problems which can occur with limestone require some degree of moisture to occur, however other problems such as wind erosion and vandalism may occur independently.
Limestone subjected to exterior exposures deteriorates due to weathering or the natural effects of wind, rain, and thermal change. Limestone is extremely durable. It does, however, absorb water and, since it is a carbonate rock, it is highly reactive when exposed to acids or even mildly acidic rain water, and it can suffer substantial deterioration.
The most common effect of weathering and erosion is loss of precise detail. Little can be done to restore edge detailing short of re-carving the stone which is usually infeasible. Erosion can be the result of general weathering described above, or it can be a more localized phenomenon based upon handling or exposure. Wind driven airborne abrasives may selectively wear away detailing on certain elevations, based upon the direction of prevailing winds.
It would have to be consistent with appropriate policy for the management of cultural landscapes. It may, however, be cost effective when considering the extended life of the stone. The symptoms of erosion can be as simple as the loss of edge sharpness as described above, or it can be very localized, specific wear due to contact with landscaping and mowing equipment. Localized damage due to contact by mowing or other maintenance equipment is preventable.
Where there is evidence of recurrent physical damage, steps should be taken to protect the resource s. Discoloration of the limestone, whether general or localized, is staining. Staining, may be the result of exposure to a variety of exterior substances or to internal occlusions in the stone or structural elements.
Some of the most common types of staining and the causative agents are:. The edges of the staining will generally be diffused, especially after an extended period. There are standard techniques for removing oil and grease stains. This condition is indicative of a certain brittleness or tendency of the stone to break up or dissolve. It may be caused by an inherent weakness in the limestone or gradual breakdown of the binder, or it may be the result of external factors affecting the strength and durability of the limestone.
This condition may be caused by the use of de-icing salts, or any other source of salt migration, such as that which can occur when rising damp is present.
There is currently little which can be done to repair the damage once this condition has developed, however the early detection of potential problems and elimination of sources of salts is critical to arresting the process. When this condition is severe and obviously caused by the heavy or inappropriate use of de-icing salts, it is sometimes called "Salt Fretting".
Regular preservation maintenance may eliminate the causes promoting crumbling, however, once the condition has occurred, its correction or repair is beyond the level of a maintenance procedure. The separation of small pieces or larger fragments from a masonry unit, frequently at the corners, edges or mortar joints is known as chipping.
These fractures are generally caused by deterioration and repointing, especially due to the use of too hard a mortar, or by accident or vandalism. Repairs include detachment repairs, patching and splicing. Repair of chipped stone requires a skilled mason and is not a maintenance procedure. If chipping is due to occasional impact from mowing or other landscape maintenance, steps should be taken to prevent future damage. For specific guidance on repairing chips in limestone, see R.
It results from a variety of causes, such as structural overloading due to settlement, the use of too hard a mortar mix or a flaw in the material. Minor cracking may be no problem, in and of itself, but it can be an indication of structural problems and the cracks can be a point of entry of water into the interior of the stone, promoting salt migration.
Cracking, which allows water or salts to enter the stone, increases the possibility of failure along the limestone and may result in subsequent spalling. Repairs include patching and replacement.
For specific guidance on repairing cracks in limestone, see R. This is not a failure of the material per se but a failure of the construction system, i. The definition implies that the failed component survives intact and may be re-installed using appropriate mechanical techniques.
Adequate pointing and caulking can prevent leakage and penetration of water into the system. For specific guidance on resecurring detached limestone blocks, see R and R. The appearance of a whitish deposit locally or uniformly over the surface may be efflorescence, the surface deposition of soluble salts. There are numerous sources for the soluble salts which create the hazy appearance; salts can come from mortar, improper cleaning agents, rising damp, de-icing salts, chemical landscaping treatments and air pollution.
Efflorescence can be a salt residue resulting from improper chemical cleaning, i. It can also be an indication of water problems. Corrective action should then be taken to eliminate the source of the problem once it is identified. Some efflorescence may occur naturally with new stones, mortar and installation materials.
The new or continued appearance of efflorescence is a stronger indicator of problems like rising damp or inappropriate cleaning methods, all of which should be referred to the Regional Historic Preservation Officer RHPO. For specific guidance on removing efflorescence from limestone, see R.
Erosion is the wearing away of the material surface by the natural action of wind, windblown particles and water. It can occur with limestone as well as any exposed materials. Inspections should include examination for any apparent loss of detail and edge sharpness which could be due to erosion. Erosion may be less of a problem on rock-faced or quarry-faced marble, but may be a more serious problem on stone with more precise detail.
Little can be done to correct this problem once it occurs, other than to protect the surface from further exposure. This may stop or at least retard the erosion process. This is an early stage of peeling, exfoliation, delamination or spalling evidenced by the detachment of small flat thin pieces of the outer layers of stone from a larger piece of stone.
Flaking is usually caused by capillary moisture or freeze-thaw cycles which occur within the masonry. The problem can also occur due to sub-florescence, so that if flaking occurs, the area should be examined to determine if salt crystallization is occurring in the flaked areas. Peeling is the flaking away of the stone surface from the substrate in strips or layers.
It may also result from a defect in the stone, or from weathering. Encrustations of the surface caused by chemical reactions with environmental elements may also peel or flake along the bedding plane.
Rising damp is the suction of ground water into the base of masonry through capillary action. During active wet periods, rising damp may be visible as a darkening of the stone along the base at ground level.
Due to the continuous changing of the moisture level due to varying exposure conditions, staining or efflorescence may be visible at a range of several feet up from the ground. Spalling is the separation and breaking away of pieces of stone due to sub-florescence, freeze-thaw, improper repointing withtoo hard a mortar mixcontaining too much portland cement, or structural overloading of the stone.
Spalling is less frequent with limestone than with sedimentary stones which are also less hard. Limestone is hard enough to resist internal forces which would cause spalling in other natural stones or fabricated masonry. This is a potentially harmful internal accumulation of soluble salts deposited under or just beneath the masonry surface as moisture in the wall evaporates.
The build-up of salts and their crystallization can create substantial pressures within the masonry, causing pieces to break off along the planes of deposition. Efflorescence at the surface is an indication that sub-florescence is possible.
Techniques for mitigating the problem include poulticing, removal of identified salt sources, elimination of moisture in the stone and damp- proofing. Please try again later. No results could be found for the location you've entered.
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That type of environment is where organisms capable of forming calcium carbonate shells and skeletons can thrive and easily extract the needed ingredients from ocean water. When these animals die, their shell and skeletal debris accumulate as a sediment that might be lithified into limestone. Their waste products also contribute to the sediment mass. Limestones formed from this type of sediment are biological sedimentary rocks. Their biological origin is often, but not always, revealed in the rock by the presence of fossils.
Sometimes evidence of a biological origin is destroyed by the action of currents, organisms, dissolution, or recrystallization. The main platform is over miles wide, and a great thickness of calcium carbonate sediments have accumulated there.
In this image the dark blue areas are deep ocean waters. The shallow Bahamas Platform appears as light blue. Enlarge image. Some limestones form by direct precipitation of calcium carbonate from marine or fresh water.
Limestones formed this way are chemical sedimentary rocks. They are thought to be less abundant than biological limestones. Most biological limestones contain significant amounts of directly precipitated calcium carbonate. After the biological grains have accumulated and are buried, water that is saturated with dissolved materials moves slowly through the sediment mass. Calcium carbonate, precipitated directly from solution, forms as a "cement" that binds the biological grains together.
If the biological grains are not cemented together, a rock will not be formed. Many limestone-forming environments are active on Earth today. Most of them are found in shallow parts of the ocean between 30 degrees north latitude and 30 degrees south latitude. One of these areas is the Bahamas Platform, located in the Atlantic Ocean about miles southeast of southern Florida see satellite image.
There, abundant corals, shellfish, algae, and other organisms produce vast amounts of calcium carbonate skeletal debris and fecal matter that completely blanket the platform. This is producing an extensive deposit of calcium carbonate sediment that has already converted to limestone at depth. Here stalactites, stalagmites, and flowstone adorn the roof, floor, and walls of the cave.
These rocks are a variety of limestone known as travertine. Limestone can also form through evaporation. Stalactites, stalagmites, and other cave formations often called "speleothems" are examples of limestone that formed through evaporation. In a cave, droplets of water seeping down from above enter the cave through fractures or other pore spaces in the cave ceiling. There they might evaporate before falling to the cave floor. When the water evaporates, any calcium carbonate that was dissolved in the water will be deposited.
Over time, this evaporative process can result in an accumulation of icicle-shaped calcium carbonate on the cave ceiling. These features are known as stalactites. If droplets fall to the floor and evaporate there, stalagmites could eventually grow upwards from the cave floor. The limestone that makes up these cave formations is known as "travertine," a chemical sedimentary rock. A rock known as "tufa" is a limestone formed by evaporation at a hot spring or on the shoreline of a lake in an arid area.
All limestones contain at least a few percent other materials. These can be small particles of quartz , feldspar , or clay minerals delivered to the site by streams, currents and wave action. Particles of chert , pyrite , siderite, and other minerals can form in the limestone by chemical processes. See our article about the " acid test " for identifying carbonate rocks and minerals.
There are many different types of limestone - each with its own name. These names are often based upon how the rock formed, its appearance, its composition, or its physical properties.
Here are some of the more commonly encountered types of limestone. Chalk: A fine-grained, light-colored limestone formed from the calcium carbonate skeletal remains of microscopic marine organisms.
Chalk is the name of a limestone that forms from an accumulation of calcareous shell remains of microscopic marine organisms such as foraminifera.
It can also form from the calcareous remains of some marine algae. Chalk is a friable limestone with a very fine texture, and it is easily crushed or crumbled. It is usually white or light gray in color.
In the past pieces of natural chalk were used to write on blackboards. Today, most blackboard chalk is a man-made product. Some of it is made from natural chalk along with additives that improve its performance. Coquina: This photo shows the shell hash known as coquina. The rock shown here is about two inches five centimeters across. A small amount of calcareous cement usually binds the grains together. The sediments that form coquina accumulate on beaches where wave action delivers an abundance of locally produced biological grains, while a significant amount of other material is not deposited.
Coquina might be composed of mollusk, gastropod, brachiopod, trilobite, coral, ostracod or other invertebrate remains. See accompanying photo or read an entire article about coquina here. Crystalline Limestone: A specimen of limestone that has been subjected to metamorphism. Some might call this material "crystalline limestone" - however, the proper name is marble.
If you view this rock closely by eye, or better, with a hand lens, you will clearly see cleavage faces of calcite intersecting at rhombic angles. The rock shown here is about four inches ten centimeters across. When limestone is subjected to heat, pressure, and chemical activity, the calcite in the rock begins to transform. This is the beginning of the process known as metamorphism. Starting at a microscopic scale, the calcium carbonate in the rock begins to crystallize or recrystallize into fine-grained calcite crystals.
As the duration and intensity of metamorphism continues, the calcite crystals increase in size. When the calcite crystals are large enough to be visible to the eye, the rock can then be recognized as marble - a metamorphic rock. Marble is the name of the metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. It is composed of calcium carbonate CaCO 3 and usually contains other minerals that might include clay minerals, micas, quartz, pyrite, iron oxide, and graphite.
At this location, and many other locations, the Kaibab Limestone is fossiliferous and dolomitic. Photograph by the United States Geological Survey. Dolomitic limestone is a rock composed mainly of calcite, but some of that calcite has been altered to dolomite.
Dolomite is thought to form when the calcite CaCO 3 in carbonate sediments or in limestone is modified by magnesium-rich groundwater. The available magnesium facilitates the conversion of calcite into dolomite CaMg CO 3 2.
This chemical change is known as "dolomitization. Dolomitization can completely alter a limestone into a dolomite, or it can partially alter the rock to form a "dolomitic limestone. Fossiliferous Limestone: Ammonite fossils found in limestone quarry in Germany. Ammonite fossils are abundant in the area around Nuremberg and Stuttgart.
Fossiliferous limestone is a limestone that contains obvious and abundant fossils. They are usually marine invertebrates such as brachiopods, crinoids, mollusks, gastropods, and coral. These are the normal shell and skeletal fossils found in many types of limestone. Fossiliferous limestone often contains information about the environment of deposition, and where the organisms lived or were deposited.
Paleontologists can often examine the fossils and determine the geologic age of the rock. Lithographic Limestone: In , workers at NOAA's printing shop ink a slab of lithographic limestone that contains an image of a nautical chart. In , NOAA produced approximately , lithographic prints using this method. A crop from an image in the NOAA archive. Lithographic limestone is a dense rock with a very fine and very uniform grain size. It occurs in thin beds which separate easily to form a very smooth surface.
In the late s, a printing process known as lithography named after the stones used was developed to reproduce images by drawing them on the stone with an oil-based ink, then using that stone to press multiple copies of the image.
Lithographic printing developed into an art form that produced many of the finest maps, navigational charts, posters, and bookplates of the 18th and 19th century. Printing with large stones weighing hundreds of pounds to over one ton was cumbersome work. Eventually lithographic printing was done using high-speed presses in which the image was inked on metal rollers and transferred onto sheets or rolls of paper as they streamed through the press.
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