Dodecahedron Geode

February 26, 2012

Dodecahedron_alana_fall 2011_700

Photographer: Alana Ketcham
Summary Authors: John Stetson; Stu Witmer

My photography student, Alana Ketcham, and I were pleasantly surprised to find a dodecahedron inside this geode at the L.C. Bates Museum. A dodecahedron is a solid composed of twelve regular pentagons, and it is one of the Platonic solids. In Ancient Greece, the Pythagoreans believed that these solids were fundamental to the universe. More recently, a group of cosmologists has proposed that our universe may be shaped like a dodecahedron (Poincare Dodecahedron Space).
Since the crystal in the picture appears to be a dodecahedron, and crystals are made of the most efficient packing of atoms, the atomic structure of this crystal would likely consist of dodecahedrons. That would mean that there are many, many dodecahedrons to be found. A dodecahedron even appears in the novel, "The Phantom Tollbooth"; that's where Alana, the photographer, first encountered a dodecahedron.
Geode, meaning earthlike, is a good description for the shape of these surprising rocks. The plain-looking chalcedony exterior, called a rind, often hides a stunning crystalline interior of quartz or other rock crystal, in this case, calcite. Geodes form as concretions in cavities as diverse as air bubbles in rocks or tree roots. Over time, they gain a shell that’s penetrated by water dissolving the interior rock and allowing crystals to grow from minerals brought in by the water. Photo taken October 23, 2011. [Revised May 2017]

Photo Details: Camera Maker: NIKON CORPORATION; Camera Model: NIKON D300; Focal Length: 105.0mm; Aperture: f/20.0; Exposure Time: 0.0040 s (1/250); ISO equiv: 200; Software: Adobe Photoshop CS Windows.