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Formula: K(NaMn)CaNa3AlMn13(PO4)12(OH)2
Anhydrous phosphate containing hydroxyl, arrojadite group,
manganese-bearing mineral,
forms a series with arrojadite-(KFe)
Crystal System: Monoclinic
Specific gravity: 3.38 to 3.41 measured, 3.42 calculated
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
Environments
Dickinsonite-(KMnNa) 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-(KMnNa) 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-(KMnNa) 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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