The Collaborative International Dictionary of English v.0.48:

Siderite \Sid"er*ite\, n. [L. sideritis loadstone, Gr. ????,
   ????, of iron, from ???? iron.]
   1. (Min.)
      (a) Carbonate of iron, an important ore of iron occuring
          generally in cleavable masses, but also in
          rhombohedral crystals. It is of a light yellowish
          brown color. Called also sparry iron, spathic
          iron.
      (b) A meteorite consisting solely of metallic iron.
      (c) An indigo-blue variety of quartz.
      (d) Formerly, magnetic iron ore, or loadstone.
          [1913 Webster]

   2. (Bot.) Any plant of the genus Sideritis; ironwort.
      [1913 Webster] Siderographic

WordNet (r) 3.0 (2006):

siderite
    n 1: iron ore in the form of ferrous carbonate [syn: siderite,
         chalybite]
    2: a meteorite consisting principally of nickel and iron