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March-April 2011

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Collector's Note: The Surprise Pocket, Gilman Notch, Center Ossipee, Carroll County, New Hampshire

Arguably the greatest thrill for any serious field collector is discovering, opening, and collecting an oversized, jam-packed crystal pocket. Unfortunately, it's an event that most field collectors never experience. When such an exciting find does occur, it's a thrill that we believe should be shared with the mineral collecting community. The tale of the Surprise Pocket is such a story—with an appalling twist—as told through the eyes of coauthor Jon Herndon.

Geology of the Ossipee Area

The Ossipee Mountains are an outstanding example of a ring dike structure, with only the basement complex of the volcano now showing. The Ossipee ring dike is composed of Albany Quartz Syenite. This material was injected from below during the collapse of the volcano, forming the ring structure. The magma chamber of the volcano (the area inside the dike) is composed of Conway Granite. This is where all of the pockets are found. The crystal-filled pockets are miarolitic cavities that were formed during the cooling of the granite. As the granite cooled, joint sets were created, and an injection of material into the joint sets produced the mineralization. A joint is a fracture in rock where there has been no lateral movement along the plane of the fracture (up, down, or sideways) of one side relative to the other. Joints normally have a regular spacing related to either the mechanical properties of the rock or the thickness of the pegmatite layer involved. Joints generally occur as sets, with each set consisting of joints subparallel to each other.

Jonathon Herndon has been an ardent field collector for more than twenty-five years, with a special focus on the Ossipee Mountains since 1983.

Eric S. Greene, an avid field collector, operates Treasure Mountain Mining, an online mineral business.

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