Beschreibung:

Aqua Calientes, Sonora, Mexico The world's only known fire agate deposits fall within two general areas-the Sonoran Desert region, stretching from southwest United States to northern Mexico, an area starting 100 miles north of Mexico City and lying between two north-south mountain ranges, the Sierra Madre Occidental and the Sierra Madre Oriental. These areas were subjected to extensive volcanic activity mostly during the Tertiary Period, 24 to 36 million years ago, relatively recent by geologic standards. With colors often more vibrant than opal and less directional, fire agate is also more durable for daily wear. Not a well known gem, fire agate, a variety of chalcedony, is thought to form by volcanic activity when hot water saturated with colloidal silica and iron oxide invades cavities in the host rock below the earth's surface. During the cooling process chalcedony with iron oxide begins to grow on any available surface with many shapes and colors being formed by the mineral impurities. Known as schiller, the alternating silica and iron oxide layers, diffract and allow light to pass and form interference of colors known as "fire". The iron oxide is what gives this gem its characteristic brown body color. Polishing fire agate is done in such a way as to follow the natural contours of the stone until only the fire is visible. Characterized by a deep, rich brown body color with a whole host of colors in its iridescence: orange, green and yellow which roll over its contour polished botryoidal surface. This excellent ring-sized stone which could be mounted either vertically or horizontally. Weighing approximately 15.65 carats and measuring 22.8 x 13.23 x 6.79 mm