Sunbeams Through a Moonstone

July 11, 2018


: Mario Freitas
Summary Author: Mario Freitas

Moonstones are composed of thin intergrowing layers of orthoclase and albite and two feldspars that differ slightly in refractive index. They can produce enchanting visual effects in the presence of white light, known as adularescence, due not to intrinsic mineral colors but rather to wave interference arising from the inner layer structure.

During the Art Nouveau period, moonstone was widely used in jewels, such as those signed by artist René Lalique. Its popular name dates from ancient Rome, where such gems were associated with the goddess Diana, supposing that their formation was caused by frozen moonlight.

In the photo above afternoon sunlight illuminates a polished moonstone. A ghostly blue glare emanates from deep inside the translucid body, and in the book page beneath it, the sketch of a crescent Moon with earthshine displays the projection of bright orange caustics. The book is a Brazilian edition of Sidereus Nuntius, the treatise Galileo published in 1610, including drawings by the author himself, based on his observations of celestial bodies through a telescope. Photo taken in Curitiba, Brazil, on May 17, 2018.