How tiny crystals decorate iris agates. (formation of quartz stone)(Brief Article) From: Science News | Date: September 16, 1995| Author: Lipkin, Richard | COPYRIGHT 1995 Science Service, Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan.  All inquiries regarding rights should be directed to the Gale Group.Copyright information

Agate, a type of quartz whose iridescent patterns sparkle with color, has long been valued as a semiprecious stone. Now, scientists can explain how its elegant swirls form.

Peter J. Heaney, a geologist at Princeton University, and Andrew M. Davis, a geological chemist at the University of Chicago, show that concentric shells of fine and coarse crystals alternate to create agate's light-diffracting "iris" bands.

Agate, formed when mineral-rich water flows through vol...