igneous

André Landed Here Rock (Glacial Erratic)

Granodiorite / Diorite (compositional estimate)

Hardness: 6–7 on Mohs scale. Color: Mottled grey and white with dark flecks. Luster: Dull/earthy (weathered surface) to vitreous (fresh crystals). Structure: Phaneritic (coarse-grained). Specific Gravity: ~2.6–2.8.

Hardness: 6–7 on Mohs scale
Color: Mottled grey and white with dark flecks
Luster: Dull/earthy (weathered surface) to vitreous (fresh crystals)

Identified December 25, 2025More igneous →

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Physical properties

Formation & geological history

This is a glacial erratic, a rock moved by glacial ice during the Pleistocene epoch. It likely originated from the Hudson Highlands and was deposited at its current location near the Hudson River during the retreat of the Laurentide Ice Sheet approximately 12,000 to 18,000 years ago.

Uses & applications

Historically used as a landing marker and memorial. Industrially, such hard igneous rocks are used as riprap for shoreline protection and construction aggregate. This specific rock serves as a historical monument for the American Revolution.

Geological facts

This specific boulder, located in Haverstraw, New York, marks the spot where British Major John André landed on September 21, 1780, to meet American traitor Benedict Arnold. It is a key site in the 'Treason' plot to surrender West Point. The inscription was added much later by local historians to commemorate the event.

Field identification & locations

Identify in the field by its coarse-grained crystalline texture, rounded 'boulder' shape typical of glacial transport, and distinctive historical carving. It is found along the shoreline of Haverstraw Beach State Park. Collectors should note that as a historical monument on State Park land, it is protected and must not be sampled or defaced.

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