Epidote

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Epidote
Specific gravity
3.38–3.49
Optical propertiesBiaxial (-)
Refractive indexnα = 1.715–1.751
nβ = 1.725–1.784
nγ = 1.734–1.797
Birefringenceδ = 0.019–0.046
PleochroismStrong
References[2][3][4]

Epidote is a

sorosilicate mineral
.

Description

Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH),

orthorhombic mineral zoisite.[6] The name, due to Haüy
, is derived from the Greek word "epidosis" (ἐπίδοσις) which means "addition" in allusion to one side of the ideal prism being longer than the other.

Epidote is an abundant rock-forming mineral, but one of secondary origin. It occurs in

adularia, calcite, and apatite; the Ala valley and Traversella in Piedmont; Arendal in Norway; Le Bourg-d'Oisans in Dauphiné; Haddam in Connecticut; Prince of Wales Island in Alaska, here as large, dark green, tabular crystals with copper ores in metamorphosed limestone.[6]

The perfectly transparent, dark green crystals from the Knappenwand and from Brazil have occasionally been cut as gemstones.[6] The green part of several mixed-rock ornamental stones is composed of epidote. These include Unakite and Australian Dragon Bloodstone.

Related species

Belonging to the same isomorphous group with epidote are the REE-rich allanite (containing primarily lanthanum, cerium, and yttrium), and the manganese-rich piemontite.

Piemontite occurs as small, reddish-black, monoclinic crystals in the manganese mines at San Marcel, near Ivrea in Piedmont, and in crystalline schists at several places in Japan. The purple color of the Egyptian porfido rosso antico is due to the presence of this mineral.[6]

Allanite and

Jöns Berzelius in 1818 to a hydrated form found as slender prismatic crystals, sometimes a foot in length, at Finbo, near Falun in Sweden.[6] Dollaseite is less common, famous from the Ostanmossa mine in the Norberg district of Sweden
.

Gallery

  • Epidote from Alaska
    Epidote from Alaska
  • Deformed epidote within greenschist rock from Itogon, Philippines
    Deformed epidote within greenschist rock from Itogon, Philippines
  • Sample of dollaseite (dark brown matrix at arrow points) from Sweden
    Sample of dollaseite (dark brown matrix at arrow points) from Sweden
  • Well-developed epidote prismatic crystals from Russia
    Well-developed epidote prismatic crystals from Russia

References

  1. S2CID 235729616
    .
  2. ^ Epidote. Handbook of Mineralogy
  3. ^ Epidote. Mindat
  4. ^ Epidote. Webmineral
  5. ^ "About Epidote".
  6. ^ a b c d e  One or more of the preceding sentences incorporates text from a publication now in the public domain: Spencer, Leonard James (1911). "Epidote". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 9 (11th ed.). Cambridge University Press. p. 689.

External links

Wikimedia Commons has media related to Epidote.
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