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Karst phenomena

Karst phenomena are the result of chemical impact of surface water and groundwater on rocks. The term karst comes from the name of a plateau in Slovenia, where these phenomena are very common. Karstification is undergone especially by limestones, but also by dolomites, gypsum, chalk and rock‑salt. Water saturated with carbon dioxide, which comes from the air and from rotting organic remains, reacts with the components of rocks, e.g., with calcite. Reducing the amount of carbon dioxide in the solution, as a result of evaporating water, causes a reverse process, i.e., slow crystallization of calcium carbonate:

${\text{Ca(HCO}}_{\text{3}}{\text{)}}_{\text{2}}\stackrel{\text{ temp.}}{\to }{\text{ CaCO}}_{\text{3↓}}\text{ + }{\text{H}}_{\text{2}}\text{O + }{\text{CO}}_{\text{2}}^{\text{↑}}$

Precipitation of calcium carbonate from the solution flowing down from the cave's ceiling leads to the formation of dripstones which can take various forms, e.g., stalactites, stalagmites, stalagnates. The intensity of limestone's dissolving depends on many factors: climate, amount of rain (more rapid in humid climates), carbon dioxide content in water, altitude above sea level (in high areas, water circulates longer, so it acts more intensively on rocks), lay of the land (the flatter the area, the greater water's penetration).

Use of calcareous rocks

Limestone is mainly used in the construction industry. Many historical buildings were erected using limestone, such as the medieval St. Florian's Gate in Kraków and the mascarons at the Kraków Cloth Hall, or the castles along the Trail of the Eagle's Nests. On a large scale, it was a local building material from which houses and farm buildings were built.

Marble is a very good sculptural material, highly appreciated by artists. The interesting range of colors, unique design and prevalence of calcite, whose hardness on the Mohs' scale is 3, result in ease of processing and application mainly in interior design. Marble slabs are used to make floors, stairs, window sills, elements of fireplace finishes, vases, sculptures etc.
Furthermore, marble is an extremely attractive building material. Some of the world's most beautiful buildings were erected using this stone.

Chalk is a rock which is added to white paints, putty, powders and toothpastes. It is used in the ceramic, chemical, pharmaceutical and cosmetic industries. After mixing with gypsum, it is used to produce writing chalk.

Properties of calcareous rocks

Limestones are a group of rocks very diverse in terms of physicochemical aspects. Their color is usually white, light gray or beige. Sometimes, depending on chemical admixtures (such as: quartz, dolomite, pyrite), limestones can be red, greenish or brown. They are poorly resistant to weather conditions. It is a raw material that is easy to process.

Conclusion

• Many sedimentary (limestone, chalk) and metamorphic (marble) rocks contain calcium carbonate.

• Roasting of limestones results in quicklime. It is used for the preparation of slaked lime, carbide, as a fertilizer for liming of soils, insecticide, etc.

• Under the influence of water rich in carbon dioxide, limestones undergo chemical weathering, which results in the creation of Karst forms.

• Identification of calcareous rocks is carried out by means of acids, which causes foaming and releasing of colorless gas – carbon dioxide.

• Calcareous rocks are used in the following industries: construction, horticulture, agriculture, cosmetics, pharmaceuticals, ceramics, chemistry.

Keywords

calcite, slaked lime, hydrated lime, quicklime, limewater

Glossary