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Emmonsite. Locality: San Miguel Mine, Moctezuma, Sonora, Mexico (size: 6.3 x 4.1 x 1.1 cm)
Category Tellurite mineral
(repeating unit)
Strunz classification 4.JM.10
Crystal system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
Space group P1
Unit cell a = 7.90, b = 8.00
c = 7.62 [Å]; α = 96.73°
β = 95°, γ = 84.47°; Z = 2
Color Yellowish green
Crystal habit Thin to hairlike crystals, occurring in rosettes and sprays; also fibrous globular aggregates and crusts
Twinning Noted
Cleavage Perfect on {010}; good on {100} and {001}
Mohs scale hardness 5
Luster Vitreous
Diaphaneity Opaque to translucent
Specific gravity 4.52–4.55
Optical properties Biaxial (-)
Refractive index nα = 1.962 nβ = 2.090 nγ = 2.100 - 2.120
Birefringence δ = 0.138 - 0.158
Pleochroism Weak
2V angle Measured: 23°
References [1][2][3]

Emmonsite, also known as durdenite, is an iron tellurite mineral with the formula: Fe2(TeO3)3·2(H2O).[1] Emmonsite forms triclinic crystals.[1] It is of a yellowish-green color, with a vitreous luster,[1] and a hardness of 5 on the Moh scale.[2]

Emmonsite crystal spray from the Moctezuma Mine (3 mm image width)

Emmonsite was first described in 1885 for an occurrence in the Tombstone District, Cochise County, Arizona. It was named for the American geologist, Samuel Franklin Emmons, (1841–1911), of the United States Geological Survey.[1][2]

Emmonsite is found, often with quartz or cerussite in the Tombstone, Arizona area.[2] It is also associated with native tellurium, tellurite, native gold, pyrite, rodalquilarite, mackayite, sonoraite, cuzticite and eztlite.[1]


  • Frost, Ray L. and Dickfos, Marilla J. and Keeffe, Eloise C. (2008) "Raman spectroscopic study of the tellurite minerals: emmonsite Fe23+Te34+O9.2H2O and zemannite Mg0.5[Zn2+Fe3+(TeO3)3]4.5H2O." Journal of Raman Spectroscopy, 39(12). pp. 1784–1788. Found at Queensland University of Technology website; Accessed September 15, 2010.
  • W. F. Hillebrand, "Emmonsite (?) from a new locality," American Journal of Science, Series 4 Vol. 18, December 1904, P.433-434; doi:10.2475/ajs.s4-18.108.433. Found at AJS Online; Accessed September 15, 2010.