Description

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the mineral’s quartz and moganite. It has a waxy luster and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black.

“Madison Blue Agate” is the local nickname applied to the blue chalcedony found in the cliffs above Montana’s Madison River. Most of the chalcedony has jasper inclusions or is gray/blue in color.