Area collector acquires massive agate specimen
A close look at three polished agate specimens, courtesy of Phil Burgess. Agates are found in this area, primarily in the Mississippi River gravels and the surrounding hills. (Steve Van Kooten/Courier Press)
Large agate specimens that collectively weigh more than 200 pounds. The specimens were found in Chihuahua, Mexico. The two cuts of Mexican Crazy Lace agate were polished after removal. (Steve Van Kooten/Courier Press)
By Phil Burgess
I’ve always had a penchant for collecting agates ever since I was a child. An agate is a colorful, often banded type of rock (not a crystal or a gem) that is composed mostly of twisted, elongated quartz fibers that form a very tough and durable material, usually colored by various mineral impurities. Because of their hardness, they survive the weathering process while the rock formations that they formed disintegrate into the sediment.
Agates occur in volcanic rocks such as lava flows, but also occur in sedimentary rocks as well. In the Prairie du Chien, Wis., area they are found in the Mississippi River gravels and in the weathered cherts and dolostone in the surrounding hills. They are popular among collectors, some of whom cut and polish them.
The spectacular agate specimen show in the photo on page 2 is an enormous block of Mexican Crazy Lace agate found in Chihuahua, northern Mexico. The two cut and polished halves together weigh a scale-busting 206 pounds! Crazy Lace agate formed in an active fault zone in Cretaceous-age limestone in a mountainous area.
Hydrothermal solutions rising through the fault deposited layers of calcite crystals and “sagenite sprays” of needle-like minerals. Further influxes of silica-charged solutions dissolved the soft calcite and sagenite, replacing them with colorful agate but keeping the crystal form of the original minerals (geologists term these crystal replacements “pseudomorphs”). The fault remained active as the agate deposit was forming, and the deposit was repeatedly shattered and re-healed with more gate, creating what is known as a “ruin” texture.
I purchased each half of this magificent specimen from a private Iowa collector over a period of several years as I could afford. It remains the largest — and certainly one of the most colorful — Mexican Crazy Lace agate cabinet pieces I have ever seen.
