Night Sky in Yellow Sapphire
Fractures are usually not desired in gemstones, but in some cases they provide a great subject for photomicrography. When a 2.49 ct yellow sapphire from Ilakaka, Madagascar, was examined with a fiber-optic light, the scene in the figure above was revealed. It is reminiscent of a long-exposure photograph of a star-filled sky with an extraterrestrial object floating in it. In reality, this is a globular iron stain in a large fracture, but the spotted iron staining evokes a faraway planet. The colorful curved lines are conchoidal patterns in the fracture. The combination of features makes the image seem as if viewed through a telescope rather than a microscope.
Illumination is very important for capturing the iridescence effect. Only if a strong fiber-optic light is used at the correct angle relative to the fracture will the colorful curved lines be highlighted.
