Marble is a metamorphic rock with a homogeneous appearance (it does not present foliation) that is formed when limestone is subjected to the heat and pressure of metamorphism. It is mainly composed of calcium carbonate CaCO3 (calcite) and dolomite CaMg(CO3)2 and which has many unique properties that make it a valuable rock in different industries.
Thin sheet marble
It is characteristic that this metamorphic rock presents a high percentage of recrystallized calcite and dolomite.
The carbonates appear forming a polygonal texture in the form of triple points, very similar to thin-sheet quartzite, however, the marble It will be composed of calcite and dolomite mainly.
Characteristics and physical properties of marble
The marble It is a non-foliated metamorphic rock, generated by the metamorphism of limestone and dolomite.
| Marble | Characteristics and physical properties |
|---|---|
| Precursor rock (protolith) | Limestone, dolomite (dolomitic rock) |
| Type of metamorphism (origin and formation) | Regional and contact metamorphism |
| deformation temperature | High temperatures (1,065°F / 575°C or higher) |
| Chemical composition | Mainly CaCO3 (calcite) 90% and [CaMg(CO3)2] (dolomite) up to 10% |
| Color | Whites, greys, blues, reds, greens, browns, creams, yellows, pinks (depends on impurities) |
| formation pressure | 2 to 4 Kbar |
| Density or specific weight | 2.71 g/cm3 |
| Grain size | 1mm to 2cm |
| main minerals | calcite |
| accessory minerals | dolomite, diopside, graphite, tremolite, actinolite |
| Texture | Polygonal, saccharoid, also called “sugar cube”. Granular metamorphic rock, consisting of a mass of interlocking grains of calcite. |
| Structure | Non-foliated (non-foliated metamorphic rock) |
Impurities in limestone can recrystallize during metamorphism, resulting in mineral impurities in the marble, most commonly graphite, pyrite, quartz, mica, iron oxides.
In sufficient quantities, this can affect the texture and color of the marble. In addition, we can find it with some precious stones such as corundum, garnet, ruby, zircon, etc.
Its basic component is calcium carbonate, since it exceeds 90% of it. The other components, considered impurities, are those that determine the color and physical properties of the rock.
Color
The marble it is usually a light colored rock.
When formed from a limestone with very few impurities, it will be white in color.
When it contains impurities such as clay minerals, iron oxides or bituminous material, it can become bluish, gray, pink, red, yellow, black, green, it can appear mottled (splashes), veined (hatched lines) and various configurations or mixtures between them.
| marble colors | Impurities |
|---|---|
| Whites | They are rich in CO3Ca and are sometimes marked by some barely visible veins. |
| blacks and grays | Contain carbonaceous or organic substances |
| reds and pinks | They contain oligisto or red hematite. |
| Yellow, cream or brown | They contain iron in the form of limonite |
| Green | They contain magnesium silicates. |
Origin and formation
Most marbles form at convergent plate boundaries, where large areas of the Earth’s crust are exposed to regional metamorphism.
Thus, limestone buried deep in the oldest layers of the crust is subjected to heat and pressure (under metamorphic conditions) from the thick layers of overlying sediments to form a rock of interlocking calcite crystals usually destroying fossils and the sedimentary textures present in the original rock. The main agents that produce these transformations are chemically active fluids, pressure and temperature.
It can also form as a result of contact metamorphism near igneous intrusions when a body of hot magma heats adjacent limestone or dolomite into metamorphic rock.
A related rock is marble dolomitic, occurs when dolomite is subjected to heat and pressure.
Classification and types of marbles
| Types of marbles | |
|---|---|
| Classification by the size of its crystals | |
| Aphanocrystalline | |
| very finely crystalline | |
| moderately crystalline | |
| grossly crystalline | |
| very grossly crystalline | |
| color classification | |
| monocolors | When they are of a single color (white, gray, green, blue, red, pink, yellow, brown, etc.) |
| polychrome | Marbled: when stripes of a different color than the background appear. |
| Arborescent: when veins appear in all directions. | |
| Breccias: if they contain more or less angular fragments trapped in a main mass. | |
| Brocateles: analogous to the previous ones, but with smaller fragments. | |
| Fossiliferous lumaqueles: when they contain or seem to contain fossils of a different nature. |
| marble colors | Impurities |
|---|---|
| Whites | They are rich in CO3Ca and are sometimes marked by some barely visible veins. |
| blacks and grays | Contain carbonaceous or organic substances |
| reds and pinks | They contain oligisto or red hematite. |
| Yellow, cream or brown | They contain iron in the form of limonite |
| Green | They contain magnesium silicates. |
How to identify marble?
The marble it occurs in large deposits that can be hundreds of feet thick and geographically extensive.
During metamorphism, this calcite recrystallizes and the texture of the rock changes. In the early stages of transformation from limestone to marble, the calcite crystals in the rock are very small, they are recognized by a sugary glow of light that is reflected from their small hidden faces when the rock is touched to the light
The marble that has been exposed to low levels of metamorphism will have very small calcite crystals. The crystals get larger as the level of metamorphism progresses. The clay minerals within the marble they will alter to more complex micas and silicate structures as the level of metamorphism increases.
Uses of Marble
- Very few rocks have as many uses as the marble, but most of this material is used as crushed or dimension stone
- Crushed stone is used as an aggregate in highways, railroad beds, building foundations, and other types of construction.
- Dimension stone is produced by sawing marble into pieces of specific dimensions. Due to their beauty, these are used in monuments, buildings, sculptures, pavements and other projects.
- The extremely high purity marble with a bright white color is very useful, after its extraction and respective processing the resulting product is called “whiting used as coloring agent and filler in paint, lime, putty, plastic, grout, cosmetics, paper, etc.
- Due to its chemical properties it is also used to produce pharmaceuticals and agriculture.
- The low hardness and solubility of marble allows its use as a calcium additive in animal feed.
- The world’s main marble producer is Novelda, a city known as “the country of marble”.
