Orange Pond Rock

March 11, 2025

Summary of Known Information About the Rock from Orange Brook, Orange, NH

Physical Characteristics

• Size: 4” x 4” x 3”
• Weight: 5.4 lbs (2,451.4 g)
• Density: ~3.12 g/cm³

Appearance & Texture

• Banded structure visible, indicating a metamorphic rock with alternating mineral layers.
• Medium to coarse-grained, with interlocking crystalline texture.
• Light and dark mineral layers, characteristic of gneiss.
• Granular but not flaky, ruling out schist.

Mineral Composition

• Quartz and Feldspar: Present in the lighter-colored bands.
• Biotite or Amphibole (Hornblende): Present in the darker bands.
• No Calcite or Dolomite: Confirmed by lack of reaction to vinegar (no carbonate minerals).
• No Magnetite or Pyrrhotite: Confirmed by lack of magnetic attraction.

Geological Classification

• Rock Type: Gneiss (high-grade metamorphic rock).
• Parent Rock: Likely granite or granodiorite, which underwent metamorphism.
• Age: Devonian (~400 million years old).
• Metamorphism Event: Likely formed during the Acadian Orogeny.

Regional Geology

• Location: Orange Brook, Orange, New Hampshire, near the intersection with Tuttle Hill Road.
• Geological Region: Part of the Bronson Hill Anticlinorium, a belt of metamorphic and igneous rocks.
• Bedrock Unit: Likely from the Kinsman Granodiorite or Littleton Formation.
• Tectonic History: Formed deep underground under high pressure and heat, then uplifted and exposed.
• Glacial Influence: Could have been transported or shaped by glaciers during the last Ice Age.

Conclusion

The rock is gneiss, a high-grade metamorphic rock formed from granite or granodiorite under intense heat and pressure. It is part of Orange, NH’s ancient bedrock, dating back ~400 million years and shaped by tectonic forces and glaciation.

Classic Geologist Pun

"That's a gneiss rock you have there!"

(Because "gneiss" is pronounced "nice", so it sounds like you're just saying "That's a nice rock!")

Geologists love this one because gneiss is a highly recognizable, well-studied metamorphic rock, and the pun practically writes itself!