Opal-CT

A variety of Opal

Consists of packed microscopic (150-300 nm) spheres made up of tiny microcrystalline blades of Cristobalite and/or Tridymite, with water content as high as 10 wt%.

In opal-CT there is the beginning of the formation of domains of short-range ordering which have arrangements of silica and water that is similar to the arrangement of atoms in cristobalite and tridymite. The X-ray powder diffraction pattern is distinguished by the presence of a well-defined broad hump with a satellite peak on the low-angle side and a possible shoulder on the high-angle side. A second weaker peak at a higher angle is also present. The ordered regions occur in a matrix of disordered opal, but it is difficult at this time to suggest that the system is two-phase. There is no evidence yet to show that the ordered domains have lost their water and are anhydrous. The fraction of the material which is composed of ordered domains is very small. The term micro-crystalline should not be applied to this material.