Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. It is composed primarily of the mineral calcite (CaCO3) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite.
What is Marble?
Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. It is composed primarily of the mineral calcite (CaCO3) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite. Under the conditions of metamorphism, the calcite in the limestone recrystallizes to form a rock that is a mass of interlocking calcite crystals. A related rock, dolomitic marble, is produced when dolostone is subjected to heat and pressure.
How does Marble form?
Marble forms due to the metamorphism of limestone with additional presence(smaller quantities) of iron oxides and graphite. As Metamorphism progresses, the crystals grow larger and become easily recognizable as interlocking crystals of calcite.
The varying colors are resultant of amount of impurity concentration and the duration of metamorphosis.
Types of Marble
Some historically important kinds of marble, named after the locations of their quarries, include:
- Carrara (Italy)
- Pentelicus (Greece)
- Proconnesus (Turkey)
White marbles, like Carrara, have been prized for sculpture since classical times. This preference has to do with the softness and relative isotropy and homogeneity, and a relative resistance to shattering. Also, the low index of refraction of calcite allows light to penetrate several millimeters into the stone before being scattered out, resulting in the characteristic “waxy” look which gives “life” to marble sculptures of the human body.
Stages of Marble working
Block working can be briefly summed up as a four-stage process:
- Squaring off: Squaring off marble blocks is a first step of vital importance. Using cutting machinery, the rough edges of the block can be removed rapidly and with little waste. Squaring off makes for more ‘uniformly’ shaped slabs. This saves time and money at the marble-working stage for end-users. The blocks are then ready for the next stage: sawing for the production of slabs.
- Sawin: Sawing for the production of slabs is performed using diamond frame saws which enable production to all desired thickness specifications provided by customer
- Resin finishin: Once the slabs have been cut, they must undergo resin finishing – another very important process. Resin finishing is conducted by means of automatic lines. This consolidation procedure provides a means of compensating for defects by filling the small ‘flaws’, pitting or spalling frequently found in such natural materials.
- Finishin: Following resin finishing, automated lines are used for all required slab surface finishing operations: polishing, smoothing, brushing, sanding, bush-hammering, rolling etc.
What are Marble main characteristics?
- Color: Marble is usually a light-colored rock. When it is formed from a limestone with very few impurities, it will be white in color. Marble that contains impurities such as clay minerals, iron oxides, or bituminous material can be bluish, gray, pink, yellow, or black in color.
- Acid Reaction: Being composed of calcium carbonate, marble will react in contact with many acids, neutralizing the acid. It is one of the most effective acid neutralization materials. Marble is often crushed and used for acid neutralization in streams, lakes, and soils.
- Hardness: Being composed of calcite, marble has a hardness of three on the Mohs hardness scale. As a result, marble is easy to carve, and that makes it useful for producing sculptures and ornamental objects. The translucence of marble makes it especially attractive for many types of sculptures.
- Ability to Accept a Polish: After being sanded with progressively finer abrasives, marble can be polished to a high luster. This allows attractive pieces of marble to be cut, polished, and used as floor tiles, architectural panels, facing stone, window sills, stair treads, columns, and many other pieces of decorative stone.
How was Marble used throughout history?
No one really knows when the game of marbles first began, or when the first marble was made. It is probably fair to say that in one form or another they have been around almost as long as mankind. Archaeologists have found game boards and playing pieces in the earliest excavated graves in Egypt and the Middle East and in most other parts of the world.
Little white marbles and round pebbles were found in Austria in cavesinhabited by our Palaeolithic ancestors. They were not made of local stone so had obviously been imported. One can only speculate about their use, but they must have been of some value to their owners to have been kept and carried with them. Stone balls and pillars to form an arch were found in a child’s grave in Eqypt which was dated around 4000BC.
Where can we find Marble today?
Marble has many decorative and structural uses. It is used for outdoor sculpture as well as for sculpture bases; in architecture it is used in exterior walls and veneers, flooring, decorative features, stairways and walkways. The way in which the stone is used may be a factor in limiting or controlling the severity of exposure. The use or function of the marble may also affect the feasibility of applying certain treatments, but type of use is not the primary factor in the major types of deterioration and damage to which marble is susceptible.
info source: https://www.gsa.gov/portal/content/111858