Amesite

(repeating unit)Mg₂Al₂SiO₅(OH)₄IMA symbolAme^[1]Strunz classification9.ED.15Crystal systemTriclinicCrystal classPedial (1)
(same H-M symbol)Space groupC1Unit cella = 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 = 4IdentificationColorWhite, colorless, pink to lilac, pale greenCrystal habitCrystals form as platy to tapering elongated pseudohexagonal prismsTwinningCommon as six-fold sector twins on {001} and polysynthetic twins parallel to {010}CleavagePerfect on {001}TenacityBrittleMohs scale hardness2.5–3LusterPearlyStreakWhite with pale green tintDiaphaneityTransparent to translucentSpecific gravity2.77Optical propertiesBiaxial (+)Refractive indexn_α = 1.597 n_β = 1.599 n_γ = 1.615Birefringenceδ = 0.018Other characteristicsKaolinite-serpentine groupReferences^[2][3][4]

Amesite is a mineral with general formula of Mg₂Al₂SiO₅(OH)₄.^[3]

Amesite crystallizes in the triclinic crystal system.^[5] 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.^[4][3] 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.^[2]

Amesite is an uncommon silicate mineral which has been reported from a variety of locations worldwide.^[3] Amesite has the first reported natural occurrence of the 6R polytype for a trioctahedral 1:1 layer silicate.^[6]

References