Note 2532 — BOOK XXXVI. THE NATURAL HISTORY OF STONES.

See B. v. c. 29. Sulphuret of manganese is now known as Alabandine; it is black, but becomes of a tarnished brown on exposure to the air. It is not improbable that this manganese was used for colouring glass, and that in Chapter 66 of this Book Pliny again refers to manganese when speaking of a kind of “magnet” or load-stone. See Beckmann, Hist. Inv. Vol. II. pp. 237-8, Bohn’s Edition; who thinks, that in the present passage Pliny is speaking of a kind of marble. It is the fact, however, that Pyrolusite, or grey ore of manganese, is used, at a red heat, for discharging the brown and green tints of glass. See also B. xxxiv. c. 42, and the Note.