Mineral Information and Data:

Ca2Fe3+Al2(Si2O7)(SiO4)O(OH) [CNMNC approved formula]

Named from the Greek for increase, the base of the prism with one longer side.

IMA status : Valid species (Pre-IMA 1801) Grandfathered
(8th edition) :
58.02.01a.02  (This Dana# Changed)
  (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
Unit cell: a = 8.90 Ǻ, b = 5.63 Ǻ, c = 10.20 Ǻ, β = 115.4°
Crystal Habit: Crystals short to long prismatic, may be deeply striated; thick tabular; acicular; massive, coarse to fine granular; fibrous
Twinning: Common on {100}, contact or lamellar
Color: Yellowish green to brownish to dark green, gray, grayish
Diaphaneity: Transparent, Opaque
Luster: Vitreous, pearly, somewhat resinous
Hardness (Mohs): 6 to 7
Measured Density: 3.35 to 3.5 g/cm3
Cleavage: 1; {001} perfect
Tenacity: Brittle
Fracture: Uneven
Streak: Colorless to grayish
Geologic Setting: Characteristic of several facies of regionally metamorphosed rocks and some contaminated felsic igneous rocks; in contact zones between igneous and calcareous sedimentary rocks; from alteration of plagioclase (saussuritization).
Mineral Association: Zeolites, amphiboles, plagioclase feldspars, quartz, actinolite, calcite (greenschist facies); amphiboles, vesuvianite, scapolite, talc, wollastonite, pyroxenes, garnet (epidote-hornfels facies); pumpellyite, glaucophane, lawsonite, riebeckite, garnet, omphacite (blueschist facies)
Other Properties: Gemstone Rare.
Comments: Dana # Changed from 58.2.1a.7
Forms a series with clinozoisite.


Origin: Calumet mine, Salida, Colorado, USA
Sample size: 3.3 x 3 x 2.5 cm
Photo: Tom Loomis


Origin: Baghicha, near Skardu Dist., Northern Areas, Pakistan
Sample size: 4 x 2.5 x 2.5 cm
Photo: Tom Loomis


(zoom-in of above)


Epidote with quartz
Origin: Prince of Wales Island, Alaska
Sample size: 20 x 10 x 22 mm (bottom)


(zoom-in of above)