Yellowish crystals of the rare mineral swinefordite from the type locality in Foote Lithium mine and one of the very few localities known worldwide (Foote Mine, Cleveland County, North Carolina, United States of America). Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Swinefordite
Swinefordite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₀.₂(Li,Al,Mg,Fe)₃(Si,Al)₄O₁₀(OH,F)₂·nH₂O.
It is a member of the Clay, Smectite-vermiculite structural group.
Key properties: Mohs hardness 1; White streak; Glistening when hydrated; dull when partially dehydrated luster; optically biaxial.
IMA symbol Sfd, IMA status: approved, named in 1973.
Deposited from ground water, as coatings on the walls of fracture zones and fissures, or replacing spodumene, in a Li-Sn-rich pegmatite.
It is found associated with Spodumene, switzerite, vivianite, quartz, albite, apatite.
The name refers to Dr. Ada Swineford (1917–1993), clay mineralogist and Professor of Geology at Western Washington State College, Bellingham, Washington, USA.