Amesite

Amesite
General
Category Phyllosilicates
Kaolinite-serpentine group
Formula
(repeating unit)		 Mg2Al2SiO5(OH)4
Strunz classification 9.ED.15
Crystal system Triclinic
Crystal class Pedial (1)
H-M symbol: (1)
Space group C1
Unit cell a = 5.307(1), b = 9.195(2)
c = 14.068(3) [Å]
α = 90.09(2)°
β = 90.25(2)°, γ = 89.96(2)°; Z = 4
Identification
Color White, colorless, pink to lilac, pale green
Crystal habit Crystals form as platy to tapering elongated pseudohexagonal prisms
Twinning Common as six-fold sector twins on {001} and polysynthetic twins parallel to {010}
Cleavage Perfect on {001}
Tenacity Brittle
Luster Pearly
Streak White with pale green tint
Diaphaneity Transparent to translucent
Specific gravity 2.77
Optical properties Biaxial (+)
Refractive index nα = 1.597 nβ = 1.599 nγ = 1.615
Birefringence δ = 0.018
Other characteristics Kaolinite-Serpentine group
References [1][2][3]

Amesite is a mineral with general formula of Mg2Al2SiO5(OH)4.[2]

Amesite crystallizes in the triclinic crystal system.[4] It contains three axes of unequal length, not at right angles.

It was first described in 1876 for an occurrence in the Chester Emery Mines, Chester, Hampden County, Massachusetts. It was named for mine owner James Ames.[3][2] It occurs in an environment of low-grade metamorphism affecting rocks with high aluminium and magnesium content. It occurs associated with vesuvianite, chlorite, magnetite, rutile, diaspore, grossular, calcite, diopside and clinozoisite in various locations.[1]

Amesite is an uncommon silicate mineral which has been reported from a variety of locations worldwide.[2] Amesite has the first reported natural occurrence of the 6R polytype for a trioctahedral 1:1 layer silicate.[5]

References

  1. 1 2 Handbook of Mineralogy
  2. 1 2 3 4 Mindat.org
  3. 1 2 Webmineral data
  4. ↑ Roberts, W.L. (1974) Encyclopedia of Minerals, p. 18. Van Nostrand Reinhold Company, New York, New York.
  5. ↑ http://www.minsocam.org/ammin/AM61/AM61_497.pdf


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