Antigorite

Antigorite
Antigorite crystals in serpentinite from Poland
General
CategoryPhyllosilicate
Serpentine-Kaolinite group
Formula
(repeating unit)
(Mg, Fe)3Si2O5OH4
IMA symbolAtg[1]
Strunz classification9.ED.15
Crystal systemMonoclinic
Identification
ColorGreen, yellowish-green, blueish-gray
Crystal habitMassive or platy
Cleavage(001) Perfect
FractureBrittle
Mohs scale hardness3.5–4
LusterVitreous to greasy
StreakGreenish white
Specific gravity2.5–2.6
Optical propertiesBiaxial (−)
Refractive index1.53–1.575
Birefringenceδ = 0.005–0.006

Antigorite is a lamellated, monoclinic mineral in the phyllosilicate serpentine subgroup with the ideal chemical formula of (Mg,Fe2+)3Si2O5(OH)4.[2] It is the high-pressure polymorph of serpentine and is commonly found in metamorphosed serpentinites. Antigorite, and its serpentine polymorphs, play an important role in subduction zone dynamics due to their relative weakness and high weight percent of water (up to 13 weight % H2O).[3][4] It is named after its type locality, the Geisspfad serpentinite, Valle Antigorio in the border region of Italy/Switzerland[5] and is commonly used as a gemstone in jewelry and carvings.

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ "AMCSD Search Results". rruff.geo.arizona.edu.
  3. ^ Dódony, István; Pósfai, Mihály; Buseck, Peter R. (2002). "Revised structure models for antigorite: An HRTEM study". American Mineralogist. 87 (10): 1443–1457. Bibcode:2002AmMin..87.1443D. doi:10.2138/am-2002-1022. ISSN 0003-004X. S2CID 55304426.
  4. ^ Ulmer, P.; Trommsdorff, V. (1995). "Serpentine Stability to Mantle Depths and Subduction-Related Magmatism". Science. 268 (5212): 858–861. Bibcode:1995Sci...268..858U. doi:10.1126/science.268.5212.858. ISSN 0036-8075. PMID 17792181. S2CID 12878042.
  5. ^ "Antigorite Mineral Data". webmineral.com.