Epidote Mineral Guide

Epidote

Crystal system · Monoclinic

Epidote is a silicate mineral prized by collectors for its exceptional color range, with several world-class Chinese localities.

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Elemental Composition (by mass)

Element	Mass %	Visual
O Oxygen	45.78%
Si Silicon	18.54%
Al Aluminum	17.82%
Ca Calcium	17.64%
H Hydrogen	0.22%

Computed from simplified end-member formula. Solid-solution series, water content, and trace substitutions cause real-world variation.

IMA Abbreviation (Whitney-Evans 2010)

→ Epidote

Sorosilicate

Standard symbol from American Mineralogist (Whitney & Evans, 2010). Used in thin-section labeling, phase diagrams, and IMA-style species records.

Pronunciation

/ˈɛpɪdoʊt/

↔ EP-ih-dote

Greek "addition"

Luster

vitreous

Bright pistachio green.

Color Cause (Chromophore)

Chromophore:

Fe³⁺

Mechanism:

idiochromatic

Color produced:

pistachio green

Fe³⁺ replacing Al in epidote structure.

Type Locality

Bourg d'Oisans — France

Described 1801 by Haüy

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Specific Gravity

3.38–3.49

g/cm³

medium

Pistachio green; sometimes confused with peridot.

For comparison: water = 1.00, glass ≈ 2.5, quartz = 2.65, corundum ≈ 4.00, galena ≈ 7.50, gold ≈ 19.3.

Pleochroism (trichroic)

Axis a

yellow-green

Axis b

green

Axis c

brown

Strength: strong

Pistachio-green epidote shows obvious trichroism.

Market availability: Uncommon

Found at major shows and select dealers. Quality varies by locality.

Collector tier: Cabinet Classic

World-class display species — sought after for cabinet collections, well-documented localities, frequent show-piece pieces.

Often found withFeldspar · Quartz · Calcite · Actinolite · Almandine

Mohs 6–7

Vickers (~) 820 HV

Knoop (~) 870 HK

Nickel–Strunz 9.BG.05a

Dana 58.02.01a.06

Geological setting

MetamorphicSkarnHydrothermal

Element composition by mass

Formula: Ca₂(Al,Fe)₃(SiO₄)₃(OH) · molar mass: 497.65 g/mol

O	41.79%
Si	16.93%
Fe	16.83%
Ca	16.11%
Al	8.13%
H	0.2%

Computed from atomic weights (IUPAC 2021). Site-occupancy groups (Fe,Mn) split equally.

GroupEpidote Group

Related members: Clinozoisite · Zoisite · Tanzanite

Mohs Hardness 6–7

1
Talc 2
Gypsum 3
Calcite 4
Fluorite 5
Apatite 6
Orthoclase 7
Quartz 8
Topaz 9
Corundum 10
Diamond

Epidote sits at 6–7 on the Mohs scale — harder than glass; scratches steel.

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Colors:

Streak
Gray-white

Crystal system
Monoclinic

Type localityKnappenwand, Salzburg, Austria

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SilicatesSilicates (Sorosilicates)

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TL;DR · 1 min read

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Epidote (Ca₂(Al,Fe)₃(SiO₄)₃(OH)) is a calcium-aluminum-iron sorosilicate famous for its distinctive pistachio-green to dark-green color and long striated prismatic crystals. It is the namesake of the epidote group and a widespread metamorphic indicator mineral. The Knappenwand locality in Austria is the historical world standard, producing meter-long prismatic crystals; modern collector specimens come from Alaska, Pakistan, and the Sichuan basin in China.

More minerals to explore #

Identification & care

Specimens usually show prismatic striated crystals, often tabular; also massive, granular, fibrous; radiated groups. Its color range is broad, including characteristic pistachio green ('pistachite'), yellowish green, olive green, dark green to black, and rarely colorless. The luster is vitreous, resinous, the streak is colorless to grayish, and specimens are typically transparent, translucent. The cleavage is perfect on {001}, imperfect on {100}. The fracture is irregular/uneven, sub-conchoidal, which aids identification.

Collector context

How it forms

The geological setting for Epidote is typically common in metamorphic rocks (blueschist, greenschist, amphibolite facies); contact metamorphic zones; hydrothermal veins; alteration product of plagioclase (saussuritization). It is commonly found in association with quartz, chlorite, actinolite, hornblende, garnet, calcite, prehnite.

Classic Chinese localities

**Huanggang Fe-Sn deposit** is an important Chinese source for the species.

Why collectors care

Epidote is a frequently-sought species in serious collections because its habit is recognizable, its color often strong, and its best examples unmistakable even at a distance. Chinese material has driven much of the recent visual shift in the species — sharper crystals, deeper colors, cleaner matrix.

What affects value

Value in Epidote is assessed, in typical order of weight, against: (1) locality provenance; (2) size relative to the species norm; (3) crystal form and termination sharpness; (4) color saturation and zoning; (5) transparency and internal clarity; (6) matrix quality and aesthetic balance; (7) condition (absence of damage, chips, or repair). Cleaning quality and verified locality documentation act as multipliers across the above.

Naming history

The name Epidote has a specific etymological and historical context — see Mindat's reference entry for provenance details. We have retained naming data at the record level; published prose is paraphrased from factual fields rather than copied from source.