Hydrated normal phosphate, fairfieldite group
Specific gravity: 3.15 to 3.16
Colour: White, pale grey white, creamy white
Messelite occurs principally as a late stage hydrothermal alteration product in zoned complex
Associated minerals include
hureaulite and jahnsite group minerals
At the type locality, the Messel mine, Messel, Darmstadt-Dieburg, Darmstadt, Hesse, Germany, messelite occurs in bituminous clay associated with anapaite (Mindat).
At the Prinz von Hessen Mine, Messel, Darmstadt-Dieburg, Darmstadt, Hesse, Germany, messelite occurs in the coal mine as a late hydrothermal product rimmed with anapaite in a granite pegmatite (Dana).
At the Chickering Mine, Walpole, Cheshire county, New Hampshire, USA, messelite-fairfieldite is moderately common as masses of bladed crystals to 2 mm. They occur where triphylite has altered to secondary phosphates, with ludlamite as a common associate (R&M 90.5.419)
At the Palermo No. 1 Mine, Groton, Grafton county, New Hampshire, USA, messelite occurs as a late hydrothermal mineral in the pegmatite in two ways:
Firstly, as pale greenish white to greenish grey masses associated principally with siderite, plagioclase and quartz, whilst other associated minerals include goyazite, whitlockite, herderite, amblygonite, eosphorite, brazilianite and sphalerite.
Secondly as almost pure white masses either deposited on crystals of ludlamite in veinlets cutting triphylite, or embedded in veinlets or patches of granular material composed largely of siderite, quartz and plagioclase with minor amounts of amblygonite, ludlamite, whitlockite and sphalerite (AM 40.828-833).
At the Bull Moose Mine, Custer, Custer Mining District, Custer county, South Dakota, USA, messelite occurs with hureaulite in the pegmatite (Dana).
At the Tip Top Mine, Fourmile, Custer Mining District, Custer county, South Dakota, USA, messelite occurs in altered triphylite in the pegmatite (Dana).
At Big Chief Mine, Glendale, Keystone Mining District, Pennington county, South Dakota, USA, messelite occurs in the pegmatite as large crystals with siderite and ludlamite (Dana).
Dan Patch Mine, Keystone, Keystone Mining District, Pennington county, South Dakota, USA, messelite occurs with triphylite (Dana).
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