Dickinsonite-KMnNa

specimen number:
2354105

location:
E.E. Smith Mine, Grafton Co., New Hampshire, USA

description:
Yellowish brown masses very rich on a pegmatite matrix. Excellent example for the species.

Located in Alexandria, Grafton County, New Hampshire, the E.E. Smith Mine comprises several granite pegmatite intrusions that were aggressively worked during the early 1940s to extract industrial sheet muscovite mica. Intruded into the surrounding Paleozoic metamorphic bedrock, these complexly zoned pegmatite bodies feature classic core zones and late-stage hydrothermal pockets enriched in beryllium, uranium, and iron-manganese primary phosphates. Over time, secondary alteration of these primary phosphate minerals gave rise to a rich mineral assemblage, including the uncommon mineral species dickinsonite-KMnNa. This potassium-, manganese-, and sodium-dominant member of the arrojadite group appears as vitreous, olive-green to yellowish-brown micaceous flakes and tabular crystalline masses within the altered pegmatite matrices. Following the end of active mica mining operations after World War II, the mine dumps became popular field sites for regional mineralogists and collectors hunting for micro-mount phosphate specimens and rare accessory minerals.

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