Mineralpedia Details for Fairfieldite

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Fairfieldite

Named for the type locality in the Fillow quarry in Fairfield County, Connecticut, USA. Additional localities for Fairfieldite include others in the United States including here in the Black Hills of South Dakota in the Tip Top, Bull Moose, Dan Patch, and Bob Ingersoll mines, as well as in Germany, Portugal, Spain, Russia, and a few others. Faifieldite is an uncommon mineral that occurs as an accessory in granite pegmatites.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/fairfieldite.pdf

Formula: Ca₂Mn²⁺(PO₄)₂·2H₂O
Crystal System: Triclinic
Crystal Habit: Foliated, Fibrous, Euhedral Crystals
Cleavage: Perfect, Distinct, None
Luster: Vitreous - Pearly
Color: greenish white, white, light yellow
Streak: white
Class: Triclinic - Pinacoidal
Fracture: Brittle - Uneven
Hardness: 3.5
WebMineral: View Fairfieldite
Mindat: View Fairfieldite

Fairfieldite - Messelite from Tip Top mine, Custer Co., South Dakota, United States

white, platy or lamellar Fairfieldite - Messelite crystals to 1mm. At the Tip Top mine, Messelite occurs chiefly within altered Triphylite. Fairfieldite occurs within altered Beryl with green Roscherite. It also occurs with Whitlockite which typically occurs on Quartz. Paragenetically, this specimen leans towards Fairfieldite, the Manganese end member. Associated with brown Jahnsite (or possibly Roscherite) and Whitlockite.

Pearly white, bladed crystals to 4mm of Fairfieldite-Messelite.