Prehnite

specimen number:
2072137

location:
Fairfax Quarry, Centreville, Virginia, USA

description:
Green slightly translucent semi lustrous botryoidal crystallized prehnite covering the top of matrix. In good condition with minimal damage present. Nice for this classic Virginia locality and species.

The Fairfax Quarry, located in Centreville, Fairfax County, Virginia, is a massive industrial site situated within the Culpeper Basin, a Mesozoic rift valley. Geologically, the quarry excavates a thick sill of Jurassic-aged diabase, often referred to as "trap rock," which intruded into the surrounding Triassic sedimentary rocks of the Newark Supergroup. This diabase is a dark, fine-grained igneous rock valued for its extreme toughness and durability, making it an essential source of crushed stone for construction projects throughout the mid-Atlantic region. Historically, the quarry has been in operation for decades, serving as a primary supplier of aggregate for the rapid urban development of Northern Virginia. While its primary purpose is industrial, the site has gained international fame among mineralogists for the hydrothermal pockets discovered within the cooling cracks of the diabase, which have produced some of the finest zeolite minerals in North America.

For mineral collectors, the Fairfax Quarry is legendary for its world-class specimens of prehnite and apophyllite. The prehnite from this locality is celebrated for its distinctive "light sea-green" color and its habit of forming translucent, globular (botryoidal) or "finger-like" clusters that can reach several centimeters in length. These are often found in aesthetic association with sharp, colorless to white crystals of apophyllite and delicate, radiating sprays of byssolite or white "cotton-ball" okenite. Many of the finest specimens were recovered during the mid-20th century, and they are characterized by their high luster and the sharp geometric contrast between the various silicate species. Because the quarry remains an active, high-security industrial operation, access for collecting is strictly limited, making historical specimens from Centreville highly sought-after treasures in both museum and private mineral collections.

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