Epidote: properties, varieties and value factors

Key properties

Chemical formula	Ca2(Al,Fe)3(SiO4)3(OH)
Crystal system	Monoclinic
Mohs hardness	6-7
Toughness	Fair to poor
Refractive index	1.729-1.768
Birefringence	0.0190-0.0450
Optic character	Biaxial negative; can show a pseudo-uniaxial interference figure (-)
Dispersion	0.0300
Specific gravity	3.25-3.50
Cleavage	Perfect in one direction (basal); uneven parting in a second
Fracture	Uneven to conchoidal
Habit	Elongated, striated prismatic crystals, often deeply grooved parallel to their length; also massive and granular
Lustre	Vitreous to greasy; polish: Vitreous to greasy
UV fluorescence	Generally inert in LW and SW
Pleochroism	Strong, trichroic; typical colours are green, brown and yellow
Cause of colour	Iron (Fe3+) produces the pistachio green to brownish tones; manganese colours the pink piemontite/rose epidote
Typical inclusions	Typically simple - parallel growth striations and needle-like fibres; liquid fingerprints and healed fractures; strong doubling visible
Stability	Stable to light; partly decomposed by hot concentrated hydrochloric acid and attacked by hydrofluoric acid
Heat sensitivity	Fusible under a jeweller's torch; avoid sudden heat
Care and cleaning	Warm soapy water safe; ultrasonic risky; never steam
Birthstones	None
Availability	Scarce as clean faceted material; common as a component of unakite
Recognition	Known to students through pistachio green striated crystals and its strong pleochroism

Varieties

Epidote

Colour	yellowish green (pistachio) to dark green, greenish brown and brownish black
Transparency	transparent
Clarity type	Type II - usually included
Phenomena	None
Appearance	Olive to pistachio green with a greasy vitreous polish; larger stones show brown or yellow flashes from strong trichroism and obvious doubling at the facet junctions.
Trade names	pistacite (pistachio-green epidote)
Misnomers	none significant; unakite is a granitic rock containing epidote, not a name for the gem itself
Typical sizes	usually under 5 ct; crystals are elongated so cut stones are often long ovals and emerald cuts
Cutting styles	Faceted almost exclusively; orient the table to show green over brown
Key separations	vs idocrase/vesuvianite: idocrase DR near 0.003-0.006 (no doubling) and lower RI; vs kyanite: kyanite perfect cleavage at right angles, DR only 0.012-0.016, blue body colour; vs brown-green tourmaline: tourmaline uniaxial with different pleochroism pattern; vs zoisite/tanzanite: tanzanite pleochroism blue/violet, different spectrum and heat treatment history
Sources (localities)	Austria (Knappenwand, Salzburg) • Pakistan (Gilgit-Skardu) • USA (Alaska, Prince of Wales Island) • Brazil (Minas Gerais) • Norway (Arendal) • Italy • Mexico • Mozambique
Availability	Scarce in calibrated sizes; available as collector faceted stones and as unakite slabs
Market notes	Modestly priced collector gem; fine pistachio-green clean ovals command a premium
Care notes	Warm soapy water; avoid ultrasonic and steam because of the perfect cleavage
In short	Pistachio-green, strongly trichroic epidote is a affordable collector stone, usually cut in long ovals under 5 carats. RI 1.73-1.77, negative optic sign and the strong 455 nm iron band identify it at the bench. A component of unakite and of many Alpine-type veins.

Size (ct)	USD per carat	Tier	As of
1.00–3.00	$15.00 – $60.00	commercial to fine	2026-10-26
3.00–10.00	$40.00 – $180.00	fine collector	2026-10-26

Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.

Sources

GIA gem encyclopedia · mindat.org · Wikipedia

Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.

Key properties

Varieties

Epidote

Sources

See also