When looking at a moldavite throuhg light, you might have noticed streaks inside the material. They can be seen perfectly in cut or broken moldavites, where the sculpted surface does not interfere. The best way is to use a microscope or a magnifying glass. WARNING: Do not look against the sun when using a magnifying glass, there is a risk of eye sight damage.
These smears are called shliers (from German “Schlieren”, which means glass lines). They are sometimes also called “rays”. Shlieren are one part of inhomogeneities in moldavites.
Shliers show that glass matter did not mix well enough – moldavites were in liquid consistence for a very short time. Smears have various chemical composition with varied content of siliceous oxide (SiO2) and other substances (Al2O3, FeO, K2O, CaO). It is supposed that schliers are remnants of disappeared sillica grains of size of 100μm. Also lechatelierites are of similar origin. They are bigger and more bordered.
Photographs of internal structure with gradual depth of foxus
A look into a broken moldavite.
You can see bubbles and schlierens in various depth of the moldavite.