Greenalite

Greenalite is a mineral in the kaolinite-serpentine group with the chemical composition (Fe2+, Fe3+)2-3Si2O5OH4. It is a member of the serpentine group. It is a hydrated ferrous silicate related to serpentine. It is a mineral consisting of the hydrous ferrous silicate of an earthy green color occurring as small granules in a cherty rock associated with the iron ores of the Mesabi range.

Greenalite was first described in 1903 for an occurrence in the Mesabi Range near Biwabik, St. Louis County, Minnesota and named for its green color.

General Information

  • Category: Phyllosilicates (Kaolinite-serpentine group)
  • Formula: (Fe2+, Fe3+)2-3Si2O5OH4
  • Crystal system: Monoclinic
  • Crystal class: Domatic (m) (same H-M symbol)

Fig: Greenalite

Properties

  • Color: Green, light yellow-green
  • Crystal habit: Rare minute crystals, rounded grains common; as porphyroblasts, oolites
  • Cleavage: None
  • Mohs scale hardness: 2.5
  • Luster: Dull, earthy
  • Streak: Greenish-gray
  • Diaphaneity: Translucent to subopaque
  • Specific gravity: 2.85 – 3.15
  • Optical properties: Biaxial (+)

Occurrence

Greenalite occurs as a primary phase in banded iron formations. Rocks which contain greenalite are usually bright green, pale green or pale brown. Greenalite occurs with quartz, stilpnomelane, siderite, chamosite, pyrite, and minnesotaite. It is commonly oolitic.

 

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