A field and laboratory study of the Lord Hill pegmatite, Stoneham, Maine, indicates that the pegmatite magma was mechanically injected into diorite country rock but that small amounts of quartz, muscovite, and microcline were introduced to the country rock producing a two-foot wide granitized halo around the pegmatite. Partial assimilation of the wall rock has contaminated and chemically altered at least the outermost zone of the pegmatite.

The internal structure consists of zones, replacement bodies, and fracture and cavity fillings. Three zones are recognized: border zone (outermost), wall zone, and core (innermost). Replacement bodies of cleavelandite and perthite are restricted to the core. Fracture and cavity fillings are numerous both in replacement bodies and in unreplaced core.

Twenty-four minerals have been identified, and their paragenetic relations determined.

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