As I have noted in several other posts, phosphates are among my favorite minerals (along with relatives vanadates and arsenates). Phosphate minerals contain the anion PO4 with an oxidation state of 3- arranged in a tetrahedron: 1 phosphate with an oxidation state of 5+ and 4 oxygens each with an oxidation state of 2- (for a total of 3-). In some phosphate minerals chlorine, fluorite, or hydroxide may be added as a negative anion as in the most common phosphate mineral group, apatite: hydroxylapatite Ca5(PO4)3OH; fluorapatite Ca5(PO4)3F; chlorapatite Ca5(PO4)3Cl.
Fairfieldite is a uncommon phosphate that occurs as an accessory mineral in granite pegmatites, especially those that are rich in lithium—the Type Locality in Fairfield County, Connecticut (Fillow Quarry), Cleveland County, North Carolina (Foote Quarry), Custer County, South Dakota (Tip Top Mine and others). Fairfieldite is a calcium manganese phosphate, [Ca2Mn(PO4)2-2H2O] with transparent to translucent euhedral crystals that leave a white streak. Crystals range from prismatic to equant and commonly appear as aggregates or foliated masses, rarely as radiating or fibrous. Crystals have a sub-vitreous (mostly) to pearly luster and are soft at ~3.5 (Mohs). Their color ranges from colorless to white to light yellow to perhaps greenish white. It is sort of a nondescript mineral that sort of looks like gypsum. The best bet to help identify fairfieldite is its occurrence in granite pegmatites, especially lithium rich forms.
I have not collected many minerals east of the Mississippi River—not an astounding statement when you consider that my only living stint east of the River has been about 15 feet while residing in La Crosse, Wisconsin. I have traveled extensively in the eastern U.S.; however, it seems I was always fishing, hiking, camping, seeing the sights, etc. and missed most minerals.
During one sojourn through North Carolina I did travel through King Mountain and read about the nearby Foote Lithium Company Mine. My interest in the mine, at that time, was in the lithium due to the many lithium mines in the Black Hills of South Dakota. I really could not locate much information on the Foote Mine (partially due to self- quarantine and lack of access to research libraries) except that the mine has not been active for several years, is partially reclaimed (a park), and collecting is strictly prohibited. According to MinDat, the granite pegmatite mined for lithium, tin, beryllium, niobium, tantalum, and “mica” is hosted in the Cherryville Quartz Monzonite, a Mississippian age batholith in the Carolina Piedmont Belt. The Mine has produced 161 mineral species including the Type Locality of 15 minerals, many of which are rare phosphates.