Alabaster is a mineral and a fairly common building material these days. But what is this substance? What is the chemical formula for alabaster? It’s worth saying right away that two substances can be understood as alabaster at once: calcium carbonate and calcium sulfate. Let's try to make out both of these subspecies of alabaster.
Calcium carbonate
The formula of alabaster in this case is calcium carbonate (CaCO3), which is the constituent of chalk and marble. This is what the ancient Egyptians called this mineral and actively mined it. Luxurious sarcophagi and other cult items were made from it. There are even references to it in the Bible, they call it "oriental alabaster".
Thin layers of this mineral are transparent enough to glaze windows. This was used in medieval Italy, and is even used today. True, when heated, it loses its transparency.
Today, calcite alabaster is mined in limestone caves, like marble. It is used to make vases, figurines, ceiling lamps and other decorative elements.
Calcium sulfate
Today, the word "alabaster" by default means gypsum, or raw materials for its manufacture. Formulaalabaster in this case will be calcium sulfate dihydrate (CaSO4 × 2H2O). Such a mineral is mined almost all over the globe: in Italy, France, USA, Germany, England, Russia.
When alabaster is calcined in a kiln, it loses almost all of its water and becomes gypsum. In turn, this is also very useful material. One of its distinguishing properties is fire resistance, so 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 two-water again and quickly hardens into solid rock. This property of gypsum is familiar to many. Due to this, it is used for sealing seams and cracks, wall decoration. True, often for ease of use it is mixed with cement mixtures. This allows you to adjust the characteristics of the hard material.
What's the difference?
Despite their difference in formula, alabasters look very similar. But their properties are very different. Let's analyze these differences in more detail. The formula of carbonate alabaster does not contain moisture. This makes its structure more dense, and consequently, the mineral itself becomes more solid compared to gypsum alabaster. Heat treatment allows gypsum alabaster to increase its strength, as well as some other characteristics. Carbonate alabaster is quite stable with temperature fluctuations.
There are also differences in density. Calcium sulfate alabaster is slightly less dense: 2.3 g/cm3 vs. 2.6 g/cm3 ycarbonate. It is worth mentioning about moisture resistance. Gypsum, upon prolonged contact with water, begins to crumble, but its counterpart marble can withstand moisture for a long time without changing its characteristics.
