[A]It is a synthetic material[ hardly naturally occurring] having molecular formula 2MgO.2Al2O3.5SiO2[ Magnesium alumino silicate].

[B]The broad outlook of the monohydrate of cordierite structure depicting TwoMgO;TwoAl2O3 and Five SiO2 shown in the ATTACHED FILE.

In between two H lies O.H2O molecule is a lattice water which leaves at a temperature at about 100C.

[C]The central portion of the system MgO–Al2O3–SiO2 has been studied with the aim of determining the range of solid solution, as well as the stability limits of the various structural states of the ternary compound cordierite. The previously suggested limited solid solution between cordierite of the composition 2MgO• 2Al2O3• 5SiO2 (2: 2: 5) and SiO2 is now believed to exist only metastably. Between 800° and 1,300° C the composition of cordierite was found to be invariably 2MgO. 2Al2O3 5SiO2.

[D]The occurrence of microcracks between domains larger than 40 μm was induced by the thermal expansion anisotropy of the cordierite crystal axes. As a result, the mean thermal expansion coefficient of the cordierite ceramics decreased to 0.4 × 10^−6 K^−1 from the average value of the crystal axes of 1.7 × 10^−6 K^−1.

[E]Its lower thermal expansion coefficient can be theoretically explained by partial microcracking.

{F}An extremely lightweight material with low thermal expansion and excellent strength, rigidity and thermal shock resistance [Gas Filters,Vacuum Chucks, Integrated Mirrors for Stages, Stage Parts, Wafer Holding, Transportation].

The cordierite is a compound of MgO-Al2O3-SiO2 system, with the following stoichiometric composition: 2Al2O3.5SiO2.2MgO. Presents a polymorphic structure with three different phases: the metastable (μ-cordierite), hexagonal cordierite (α-cordierite) and orthorhombic (β-cordierite). These phases, the β-cordierite in particular, have a very lower thermal expansion coefficient, a characteristic that makes them desirable for applications requiring a high shock thermal resistance.

The more frequent phase α-cordierite can be easily obtained by solid state reaction, in a temperature range between 1300-1400ºC. The low thermal expansion cordierite is related to the high anisotropy of this property according to the crystallographic axes. While in the direction of the a-axis between 0-1000ºC expansions are observed, in the direction of c-axis is a contractions occurred, thereby resulting in a very low overall expansion (or near zero), see figures.

Abdullah,

Further to my previous opinion, I suggest the reading of an article from JACS (1980) authored by DL Evans et all, which I enclose in attachement!

M.Ribeiro