Formula: K(NaMn)CaNa3AlMn13(PO4)12(OH)2
Anhydrous phosphate containing hydroxyl, manganese mineral, arrojadite group, forms a series with arrojadite-(KFe)
Specific gravity: 3.38 to3.41
Hardness: 3½ to 4
Streak: Nearly white
Colour: Green shades to dark green, yellowish green, brownish green; green in transmitted light.
Solubility: Soluble in acids


Dickinsonite is a high-temperature (about 800oC) primary phosphate in granite pegmatites (HOM), commonly associated with lithiophilite (Mindat).

At the type locality, the Fillow Quarry, Branchville, Redding, Fairfield county, Connecticut, USA, dickinsonite occurs in a pegmatite associated with eosphorite, triploidite, lithiophilite, rhodochrosite, reddingite and fairfieldite (HOM, Mindat)

At Poland, Androscoggin county, Maine, USA, in some places it appears that the dickinsonite has been altered to fairfieldite; this alteration probably explains the rarity of dickinsonite. The probable sequence of formation of the minerals in the pockets is amblygonite, lithiophilite, rhodochrosite, quartz, eosphorite, reddingite, dickinsonite, fairfieldite, apatite, landesite and manganese oxide (AM15.375).

At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, dickinsonite-(KMnNa) is commonly associated with montebrasite. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.506).

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