- Chloritoid
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Chloritoid 
Chloritoid crystal group on matrix from Nuristan Province, Afghanistan (size:6.3 x 3.5 x 3.0 cm)General Category Silicate mineral - nesosilicste Chemical formula (Fe,Mg,Mn)2Al4Si2O10(OH)4 Strunz classification 09.AF.85 Dana classification 52.03.03.01 Crystal symmetry Monoclinic prismatic 2/m or triclinic pinacoidal 1 Unit cell a = 9.50 Å, b = 5.50 Å, c = 18.22 Å; β = 101.9°; Z = 4 or
a = 9.46 Å, b = 5.50 Å, c = 9.15 Å; α = 97.05° β = 101.56° γ = 90.10°Identification Color Dark gray, greenish gray, greenish black Crystal habit Tabular pseudohexagonal crystals; rosettes, commonly coarsely foliated with foliae
typically curved or bent; also massiveCrystal system Monoclinic or triclinic Twinning Common on {001}, polysynthetic may be lamellar Cleavage Perfect on {001}, distinct on {110}; parting on {010} Tenacity Brittle Mohs scale hardness 6.5 Luster pearly on cleavage surfaces Streak White, grayish, or very slightly greenish Diaphaneity Translucent Specific gravity 3.46 – 3.80 Optical properties Biaxial (+) or (–) Refractive index nα = 1.713 - 1.730 nβ = 1.719 - 1.734 nγ = 1.723 - 1.740 Birefringence δ = 0.010 Pleochroism X = olive-green to yellow; Y = grayish blue to blue; Z = colorless to pale greenish yellow 2V angle Measured: 36° to 89° Dispersion r > v; strong References [1][2][3] 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 crystals and foliated masses. Its Mohs hardness is 6.5, 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.
Both monoclinic and triclinic polytypes exist and both are pseudohexagonal.[1][2]
It was first described in 1837 from localities in the Ural Mountains region of Russia. It was named for its similarity to the chlorite group of minerals.[2][3]
References
- ^ a b Handbook of Mineralogy
- ^ a b c Mindat
- ^ a b Webmineral data
Phosphates Childrenite · Graftonite · Lithiophilite · Natrophilite · Purpurite · Triplite · Triploidite · ZanazziiteSilicates Babingtonite · Bixbite · Braunite · Brownleeite · Calderite · Chloritoid · Eudialyte · Glaucochroite · Jeffersonite · Knebelite · Ottrelite · Piemontite · Pyroxferroite · Rhodonite · Spessartine · Sugilite · Tephroite · Zakharovite · ZircophylliteSulfides Other Axinite (borosilicate) · Geigerite (arsenate) · Manganese nodule (various) · Samsonite (Sulfosalt) · Zincobotryogen (sulfate)Categories:- Iron minerals
- Magnesium minerals
- Manganese minerals
- Aluminium minerals
- Nesosilicates
- Monoclinic minerals
- Triclinic minerals
- Silicate mineral stubs
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