Mineral Information and Data:

CaSrAl3O(Si2O7)(SiO4)(OH) [CNMNC approved formula]

Named as the Sr-analogue of clinozoite. Approved as niigataite in 2003 and named for its locality at Itoigawa-Ohmi district, Niigata Prefecture, central Japan . Name changed per nomenclature of epidote-group minerals (IMA, 2006).

IMA status : Renamed IMA Approved; 2006 ()
(8th edition) :
58.02.01a.09  (This Dana# Added)
  (58) Sorosilicate Insular, Mixed, Single, and Larger Tetrahedral Groups
  (58.02) with cations in [6] and higher coordination; single and double groups (n=1,2)
  (58.02.01a) Epidote group (Clinozoisite subgroup)
(10th edition) :
  (09) Silicates
  (09.B) Sorosilicates (dimer) structures
  (09.BG) Sorosilicates with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: P21/m
Unit cell: a = 8.890(4)Ǻ, b = 5.5878(18)Ǻ, c = 10.211(4) Ǻ, β = 115.12(3)°, Z=4
Crystal Habit: As subhedral grains, to 0.5 mm across.
Color: Pale gray color with a yellowish green tint
Diaphaneity: Transparent
Luster: Vitreous
Hardness (Mohs): 5 - 5.5
Measured Density: 3.63 (calculated) g/cm3
Cleavage: Perfect in one direction
Tenacity: Brittle
Streak: White
Geologic Setting: Found in a boulder of prehnite rock wherein the prehnite occurs as fan-shaped aggregates to 3 cm in length.
Mineral Association: Chlorite, diaspore


Boulder consisting of prehenite, diaspore, chlorite and clinozoisite-(Sr) (former niigataite). The pale lavender is prehenite/diaspore and the very pale green is chlorite/clinozoisite-(Sr) (former niigataite)
Origin: Itoigawa, river Kazuo, Niigata prefecture, Japan.
Photo: © American Mineralogist