Chloritoid

Chloritoid
Property	Value	Comments
Formula	(Fe,Mg,Mn)Al2SiO5(OH)	Mg-rich variety known as Sismondine Mn-rich variety known as Ottrelite Forms series with Carboirite
Crystal System	Monoclinic or Triclinic	2/m
Crystal Habit	Massive or Tabular
Cleavage	{001} perfect {110} imperfect {010} parting	Not visible in thin section. Twinning common on {001}.
Color/Pleochroism	(x) colorless, olive green, gray (y) blue-gray, indigo, blue-green (z) colorless, yellow-green, greenish brown
Optic Sign	Biaxial (+)
2V	36° to 89°
Optic Orientation	X or Y = b (monoclinic); Z-c angle= 2°-30°; Y = b (triclinic)
Refractive Indices alpha = beta = gamma =	1.713-1.730 1.719-1.734 1.723-1.740
Max Birefringence	0.010	High Positive Relief
Elongation	yes
Extinction	inclined
Dispersion	r > v
Distinguishing Features
Occurrence	Results from low to medium grade regional metamorphism as well as in hydrothermal environments.
Editors	Sue Scheufele (05)

	A cluster of chloritoid crystals in thin section.