Alabaster is a mineral, as well as building material that is quite common today. But what is this substance? What is the chemical formula of alabaster? It’s worth saying right away that under the alabaster you can immediately understand two substances: carbonate and calcium sulfate. Let's try to parse both of these subspecies of alabaster.
Calcium carbonate
Alabaster formula in this case is calcium carbonate (CaCO3), which is composed of chalk and marble. This is what the ancient Egyptians called this mineral and actively mined it. Luxurious sarcophagi and other cult things were made from it. It is even mentioned in the Bible; it is called "eastern alabaster" there.
Thin layers of this mineral are transparent enough to glaze windows. It was used in medieval Italy, and is even used now. True, when heated, it loses its transparency.
Today, calcite alabaster is mined in limestone caves, as is marble. Vases, figurines, plafonds and other decorative elements are made from it.
Calcium sulphate
Today, the word "alabaster" by default means gypsum, or raw materials for its manufacture. The alabaster formula in this case will be two-water calcium sulfate (CaSO4 × 2H2O). Such a mineral is mined almost all over the globe: in Italy, France, the USA, Germany, England, and Russia.
When calcining alabaster in the oven, it loses almost all of the water and becomes plaster. In turn, this is also very useful material. One of its distinguishing features is fire resistance, which is why it is used to protect against open flames and high temperatures. It is also used for soundproofing.
Gypsum, crushed into a fine powder when water is added to it, becomes bipartite again and quickly solidifies into solid rock. This property of gypsum is familiar to many. Due to this, it is used for sealing joints and cracks, wall decoration. True, it is often mixed with cement mixes for ease of use. This allows you to adjust the characteristics of the solid material.
What is the difference?
Despite their difference in formula, alabaster looks very similar. But in their properties they are very different. We will analyze these differences in more detail. The alabaster carbonate formula does not contain moisture. This makes its structure more dense, and therefore the mineral itself becomes harder than gypsum alabaster. Heat treatment allows gypsum alabaster to increase its strength, as well as some other characteristics. Carbonate alabaster is quite stable at temperature changes.
There are differences in density. Alabaster made of calcium sulfate is slightly less dense: 2.3 g / cm 3 versus 2.6 g / cm 3 for carbonate. It is worth saying about moisture resistance. Gypsum with long contact with water begins to crumble, but its fellow marble can withstand moisture for a long time without changing its characteristics.