Quartz

specimen number:
9892087

location:
Union Road, St. Louis Co., Missouri, USA

description:
Collected in the 1960s during road construction, very good example of what many call a Union Road agate. This has been polished. These are not often seen available on the market today.

The Union Road locality in St. Louis County, Missouri, is famous among mineral collectors for yielding unique concretionary agates. The primary collecting period took place during the 1960s (roughly active from 1965 through the decade), when heavy excavation for the construction and interchange of Interstate 55 and Interstate 270/255 exposed local strata. Geologically, the area consists of Paleozoic limestone and dolomite formations interspersed with chert-bearing residuum, heavily influenced by historical glacial outwash and Mississippi River terrace gravels. The so-called Union Road agates occur inside weathered concretion nodules weathered out from the limestone host rock. They typically display bleached or redistributed exterior tones of white, tan, brown, and black, occasionally featuring striking translucent quartz or smokey centers, bold banded patterns reminiscent of Fairburn agates, and rare metallic inclusions such as goethite needles or millerite. Because the original highway cuts are now completely built over by modern commercial developments and housing, active collecting has long ceased, making these distinct local agates prized old-stock collector items.

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