Siderite is an iron carbonate mineral. The only analysis of a Franklin siderite is by Lawson Bauer who found 63.55 % FeCO3, 6.01 % ZnCO3, 4.27 % MnCO3, and 23.50 % (Ca,Mg)CO3 for a specimen slightly contaminated with pyrite. The paucity of analytical data preclude even general statements about the range of solid solution among the rhombohedral carbonates at Franklin and Sterling Hill.
Siderite was first noted by Seymour (1868), tentatively accepted by Palache (1935), and confirmed by Frondel (1972). It is known from both Franklin and Sterling Hill, but is an uncommon mineral.
Siderite occurs as druses and small (1-2 mm) late-stage crystals for the most part. Crystals are rhombohedral, mostly curved, and commonly tarnished. It is light to dark brown, varying substantially within a given specimen, and easily oxidized. A density of 3.82 g/cm3 was reported by Palache (1935).
Siderite occurs in seams and vugs, sometimes forming masses, and is associated with calcite, pyrite, galena, and other common minerals. At Sterling Hill siderite occurs in vuggy areas between hematite and other carbonates. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: FeCO3
 Essential Elements: Carbon, Iron, Oxygen
 All Elements in Formula: Carbon, Iron, Oxygen
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
 To find out more about this mineral at minDat's website, follow this link   Siderite

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.615

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.76


Siderite, calcite and franklinite from the Sterling Hill Mine, NJ.
Siderite (tan to brown), calcite and franklinite from the Sterling Hill Mine, NJ. Photo by JVF.

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