Hagley Rocks!

Hagley Rocks!. . , The common name for this rock is Wilmington Blue Rock, the name of the local minor league baseball team. It is formally called Brandywine Blue Gneiss (BBG)., The rocks in Hagley's quarries began forming about 550 million years ago. Large-scale movement of the Earth's crust, called plate tectonics, continued for another 300 million years, resulting in a tremendous episode of mountain building rivaling that of the Alps and Rockies of today (Appalachian Orogeny)., The BBG was formed during the first part of this massive tectonic event as a volcanic island are system (Figure 1). The original igneous rock was then subjected to high temperatures and pressures as it was buried and squeezed (Figure 2). These forces created the tough, dense, and durable metamorphic rock that it is today., This rock served this former gunpowder manufactory brilliantly in terms of utility-it had a definite, practical effect on operations here. It withstood, or assumed, the main force of most explosions that occurred in the powder yard, thereby largely preventing even greater destruction in the wake of a blast. It is abundant within this stretch of the Brandywine Valley, thereby allowing DuPont to use it extensively as the main building material. Also, it mostly resists chemical and physical weathering, allowing the site structures to have largely remained intact for decades. As a result, it represents the ideal building stone for this former gunpowder manufactory due to its toughness, density, competence, and durability., [Right side illustrations and rock samples] , Brandywine Blue Gneiss uniquely possesses and displays many textural features characteristic of this rock type: Mineral Banding/Foliation, Augen, Migmatite, Boudinage, Schlieren, and Lineation. The first three of these are displayed in the rock samples attached to this sign., Mineral Banding/Foliation: Alternating bands of two different mineral compositions., Augen: Eye-shaped mineral crystals formed by structural deformation., Migmatite: Interbanded, streaked igneous/metamorphic "mixed” texture, Boudinage: Localized separation of mineral bands forming sausage-shaped features, Schlieren: "Oil-on-water” texture formed by deformation, Lineation: Parallel alignment of elongate minerals.