Chamosite is an iron aluminum silicate hydroxide mineral of the chlorite group. Chemical analysis by Jun Ito yielded SiO2 25.3, Al2O3 14.0, Fe2O3 2.02, FeO 21.0, MnO 9.96, MgO 7.22, ZnO 9.60, CuO 0.08, CaO 0.04, Na2O 0.02, K2O 0.08,
H2O- 0.2, H2O+ 10.6, total = 100.12 wt. %. Microprobe analysis by [Dunn] yielded SiO2 25.0, Al2O3 16.9, total Fe as FeO 25.3, MgO 5.7, ZnO 10.2, MnO 7.1, with H2O 9.8 wt. % by difference, total = 100 wt. %.
Frondel and Ito (1975), in the description of baumite, noted a brunsvigite with appreciable amounts of Mn and Zn. This material is described here as chamosite and was further discussed by Guggenheim and Bailey (1989). Chamosite is not known from Sterling Hill.
Franklin chamosite occurs as crude, radial, lustrous, 2-5 mm, greenish-black crystals in veinlets in a lizardite (baumite) assemblage. The luster is vitreous, and the density is 3.13 g/cm3.
Chamosite was found associated with crude, broken, hexagonal, barrel-shaped, prismatic crystals of willemite, abundant lizardite (baumite in part), and green crystals of aegirine. The assemblage is anomalous for Franklin, but is assuredly from here. The material was found on the Buckwheat Dump, and the known material is all from one find (J. L. Baum, personal communication). (Dunn, 1995)

 Location Found: Franklin
 Year Discovered: 1820
 Formula: (Fe2+,Mg)5Al(AlSi3O10)(OH)8
 Essential Elements: Aluminum, Hydrogen, Iron, Oxygen, Silicon
 All Elements in Formula: Aluminum, Hydrogen, Iron, Magnesium, Oxygen, Silicon
 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   Chamosite

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.470

No Images at this time.


All content including, but not limited to, mineral images, maps, graphics, and text on the Franklin-Ogdensburg Mineralogical Society, Inc. (FOMS) website is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.
Creative Commons License