Amesite

Amesite is a mineral with the general formula of Mg2Al2SiO5(OH)4. It is an apple-green chlorite mineral occurring in foliated hexagonal plates

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

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

General Information

  • Category: Phyllosilicates
  • Formula: Mg2Al2SiO5(OH)4
  • Crystal system: Triclinic.
  • Member of: Kaolinite-Serpentine Group
  • Transparency: Translucent.

Properties

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

  • 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
  • Mohs scale hardness: 2.5-3
  • Luster: Pearly
  • Streak: White with pale green tint
  • Diaphaneity: Transparent to translucent
  • Specific gravity: 2.77

Occurrence: A product of low-grade metamorphism of Al, Mg-rich rocks.

Association: Vesuvianite, chlorite (Pensacola Mountains, Antarctica); magnetite, rutile, diaspore (Chester, Massachusetts, USA); grossular, calcite, diopside, clinozoisite (Black Lake, Canada).

Distribution: At the Emery mine, Chester, Hampden Co., Massachusetts, USA. From the Lake Asbestos mine, Black Lake, Quebec, Canada. From the Postmasburg manganese deposits, Cape Province, South Africa. From Russia, at the Saranovskoye chromite deposits, Northern Ural Mountains. At HÄallefors, Sweden. On Mt. Sobotka, Silesia, Poland.

 

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