Zoisite | Gemopedia

Zoisite is a mineral species in the epidote group. The most celebrated variety is its blue to violet occurrence, tanzanite, but other zoisite colors include red, pink (thulite), green and purple. Discovered in the early 19th century, zoisite was named after Baron von Zois, an Austrian scientist and mineral collector.
Colors
Blue To Violet To Bluish Purple, Brown, Golden, Yellowish Green, Light Toned Pink, Parti-Colored Pink, Colorless

Zoisite Classification

Common Name

Zoisite

Species

Zoisite

Variety

Zoisite

Colors

Blue To Violet To Bluish Purple, Brown, Golden, Yellowish Green, Light Toned Pink, Parti-Colored Pink, Colorless

Alternate Names

Gemstone Groups

Epidote

Key Separations

refractive index, birefringence, appearance, optic character and pleochroism

Comments

Tanzanite: transparent blue to violet to bluish purple. Thulite: translucent to opaque pink, often with mottled or streaked with gray or white. Ruby in zoisite: translucent to opaque rock like ornamental material with ruby crystals in green zoisite

Zoisite Optical Properties

Transparency

Transparent - Opaque

Refractive Index

1.691-1.7
Tolerance:(+0.005/-0.005)

Birefringence

0.008-0.013

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Trichroic, (in green gems) strong green, yellow, and greenish brown

Dispersion

Strength: weak fire Value: 0.021

Comments

Zoisite Chemistry & Crystallography

Chemical Name

calcium aluminum silicate hydroxide

Chemical Formula

Ca2Al3(SiO4)3(OH)

Synthesis

Crystal System

Orthorhombic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Zoisite Characteristic Physical Properties

Hardness

6-7

Streak

White

Specific Gravity

3.1-3.45 Typical:3.35

Toughness

Varies

Inclusions

Zoisite is a type I clarity stone. Stones rarely needles, chromite inclusions, growth and etch tubes.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal, Uneven

Cleavage

Perfect, in one direction, Good, in one direction

Comments

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