Cement
calcium carbonate (limestone)
Limestone, CaCO3 decomposes into quicklime, CaO, and carbon dioxide, CO2, when heated. The reaction is: CaCO3 + heat --> CaO + CO2.
Cement is formed from limestone through a process called calcination, where limestone (calcium carbonate) is heated at a high temperature to break it down into lime (calcium oxide) and carbon dioxide. The lime is then further processed and combined with other materials like clay to create cement.
makes ceramic or porcelaine
Heating limestone with clay produces cement, which is a key component in the production of concrete. This process is known as calcination, where limestone and clay ingredients are mixed and heated to high temperatures to form a substance called clinker.
Clay can turn into limestone through a process called diagenesis, where the clay particles are subjected to compaction and cementation, forming a new rock material. Over time, the minerals in the clay are altered and precipitate out to form calcium carbonate, which is the primary mineral in limestone.
It is formed by natural processes by usually involving a mixture of limestone and clay.
To make cement in alchemy, you typically combine limestone and clay together. These two materials are heated in a kiln to high temperatures, which causes chemical reactions that result in the creation of cement.
Limestone would be potentially harder until the clay is fired. The problem we have here is that "clay" is an ambiguous term. There is no homogenous or standard formula for clay. However, clays can generally be formed and baked to become set and hard. This is called firing. Fired clay tends to be quite hard, and depending on the formula, might be harder than limestone.
The material you are referring to is likely clay. Clay is a natural earth material that becomes moldable when wet and hardens when heated, making it ideal for creating various objects such as tablets in ancient civilizations like Sumeria.
Clay or Brick
Cement is a powdered substance made primarily from limestone, clay, and other minerals like iron ore and gypsum. It is not a direct mixture of limestone and silicon dioxide. The limestone and clay are heated together to form a compound called clinker, which is then ground into a fine powder to make cement.