Min. [Named 1866, after W. W. Jefferis, of Westchester, Pennsylvania: see -ITE.] A hydrous silicate of aluminium, iron, and magnesium, in foliated crystals, like mica, exfoliating in a remarkable manner when heated.
1866. Amer. Jrnl. Sc., Ser. II. XLI. 248. Jefferisite, a new mineral species. Ibid. (1890), Ser. III. XL. 455. The analogies between kerrite and jefferisite are perfectly clear.
