Ca2 Al2 (Fe3+; Al)(SiO4 )(Si2 O7 )O(OH)

Epidotec 2001 Mineral Data Publishing, version 1.2°

Crystal Data: Monoclinic. Point Group: 2=m: Crystals prismatic, to 35 cm, commonly
elongated and striated k [010]. Fibrous, coarse to ¯ne granular, massive. Twinning: On f100g,
contact, lamellar, common.
Physical Properties:Cleavage: Perfect on f001g, imperfect on f100g. Fracture: Uneven.
Tenacity: Brittle. Hardness = 6{7 D(meas.) = 3.38{3.49 D(calc.) = 3.391{3.464
Optical Properties: Transparent to nearly opaque. Color: Pistachio-green to palegreen, yellow, yellowish green, greenish yellow, greenish black; yellow-green in thin section.
Luster: Vitreous, pearly, somewhat resinous.
Optical Class: Biaxial ({). Pleochroism: Strong; X = colorless, pale yellow, pale green; Y =greenish yellow; Z = yellowish green. Orientation: Y = b. Dispersion: r > v: ® = 1.715{1.751¯ = 1.725{1.784 ° = 1.734{1.797 2V(meas.) = 90± {116±
Cell Data: Space Group: P 21 =m: a = 8.8877(14)¯ = 115:383(14)± Z = 2

b = 5.6275(8)c = 10.1517(12)X-ray Powder Pattern: Bourg d'Oisans, [France].
2.900 (100), 2.679 (100), 2.688 (70), 4.02 (50), 2.599 (50), 2.460 (50), 3.40 (40)
Chemistry:
SiO2
TiO2
Al2 O3Fe2 O3FeO

(1)
36.52
0.00
20.97
17.22
0.45

MnO
MgO
CaO
H 2 O+

(1)
0.00
0.00
23.05
1.98

Total

100.193+(1) West¯eld, Hampden Co., Massachusetts, USA; corresponds to (Ca1:99 Fe2+
0:03 )§=2:02 Al1:94 Fe1:04(Si2:94 Al0:06 )§=3:00 O12 (OH)1:06 :Polymorphism & Series:
Mineral Group:Forms a series with clinozoisite.

Epidote group.

Occurrence: Characteristic of several facies of regionally metamorphosed rocks and somecontaminated felsic igneous rocks; in contact zones between igneous and calcareous sedimentaryrocks; from alteration of plagioclase (saussuritization).
Association: Zeolites, amphiboles, plagioclase feldspars, quartz, actinolite, calcite (greenschistfacies); amphiboles, vesuvianite, scapolite, talc, wollastonite, pyroxenes, garnet (epidote-hornfelsfacies); pumpellyite, glaucophane, lawsonite, riebeckite, garnet, omphacite (blueschist facies).
Distribution: A few notable occurrences follow for this widespread mineral. From Bourgd'Oisans, Isµere, France. At Arendal, Norway. From Traversella, Piedmont, Italy. Exceptional
crystals from the Knappenwand, Untersulzbachtal, Salzburg, Austria. In the USA, ¯ne crystals
from around Sulzer, Prince of Wales Island, Alaska; on Garnet Hill, Calaveras Co., California; atthe Calumet mine, Cha®ee Co., Colorado; in the Seven Devils district, Adams Co., Idaho; andfrom the Julie claim, Pamlico district, Mineral Co., Nevada. In Mexico, at San Quentin, Baja
California. From Naukluft Farm, Rehoboth, Namibia. In Pakistan, exceptional crystals fromTormiq.
Name:

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

Type Material:

Natural History Museum, Paris, France.

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permission of Mineral Data Publishing.

References: (1) Dana, E.S. (1892) Dana's system of mineralogy, (6th edition), 516{521.
(2) Deer, W.A., R.A. Howie, and J. Zussman (1986) Rock-forming minerals, (2nd edition), v. 1B,disilicates and ring silicates, 44{134. (3) Seki, Y. (1959) Relation between chemical compositionand lattice constants of epidote. Amer. Mineral., 44, 720{730. (4) Gabe, E.J., J.C. Portheine, andS.H. Whitlow (1973) A reinvestigation of the epidote structure: con¯rmation of the iron location.
Amer. Mineral., 58, 218{223. (5) Kvick, ºA, J.J. Pluth, J.W. Richardson, Jr., and J.V. Smith(1988) The ferric iron distribution and hydrogen bonding in epidote: a neutron di®raction study
at 15 K. Acta Cryst., 44, 351{355.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted inany form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior written
permission of Mineral Data Publishing.