Celsian

Celsian shows a c(001) perfect cleavage and a b(010) good cleavage, which marks the difference with its polymorph paracelsian which has a [110] indistinct cleavage. There are different crystals habits like adularia, larger, stout crystals (Spencer, 1941), and long, slender to acicular. It is usually colorless and transparent with a pearly to non-fluorescent luster. The density is about 3.31 to 3.33 g/cm. This might be the case due to some impurities in the structure of the mineral. It has a hardness of 6 on the Mohs scale, this hardness is due to the short length of the bond in the structure, since relatively short bonds tend to be harder.

Celsian is a barium feldspar with a chemical composition BaAl2Si2O8. It forms part of the feldspar group and belongs to the celsian-hyalophane series and the celsian-orthoclase series. It has some resemblance to anorthite, and it has four distinct polymorphs. The essential elements are silicon, aluminum, oxygen, and barium. Some common impurities in the mineral are iron, titanium, magnesium, potassium, and calcium. Celsian is stable from room temperature up to 1590 °C (Lin and Foster, 1968). The most common trace elements are potassium and calcium, in an analysis of the approximate chemical composition of celsian the following wt% were found: • SiO2—35.1 • Al2O3---26.8 • BaO----35.8 • K2O-----2.3 Total:100.0 (Newham and Megaw, 1960).

The uses of celsian are mostly related to glass and ceramics. This uses are usually achieved by the preparation of pure synthetic monoclinic celsian. Celsian has very attractive features such as chemical stability and high mechanical resistance, which can be favourably exploited in order to obtain enhanced-performance composites with respect to bulk glass. (Cannillo, Carlier, Manfredini, Montorsi, and Siligardi 2006). Many studies show that by increasing the amount of celsian phases in the glasses results in increased bulk of crystallization (Khater and Idris, 2004).