Chloritoid

Chloritoid is a silicate mineral of metamorphic origin. It is an iron magnesium manganese alumino silicate hydroxide with formula: (Fe,Mg,Mn)₂Al₄Si₂O₁₀(OH)₄. It occurs as greenish grey to black platy micaceous triclinic crystals and foliated masses. The Mohs hardness at 6.5 is unusually high for a platy mineral and it has a specific gravity of 3.52 to 3.57. It typically occurs in phyllites, schists and marbles.

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It was first described in 1837 from localities in the Ural Mountains region of Russia.

References

• Webmineral data
• Mindat