Sphalerite | Gemopedia

With greater dispersion than diamond, sphalerite is an intriguing, yet challenging, gem. Known primarily to collectors due to its lack of hardness, sphalerite can try the patience of even the most highly skilled lapidaries who dare to fashion it into a finished gem. Not only is it extremely soft, it also has perfect cleavage, in six directions, making it extremely difficult to cut and polish! Add in the fact that it's a brittle gem, and you have an idea of the challenge that awaits its potential cutter. When that talented lapidary is, however, able to complete his task with a fashioned gem, the results are more than worth the lapidary's efforts!
Alternate
Names
Cleiophane, Marmatite, Zinc Blende
Colors
Green, Yellow, Orange, Red, Brown, Gray To Black

Sphalerite Classification

Common Name

Sphalerite

Species

Sphalerite

Variety

Colors

Green, Yellow, Orange, Red, Brown, Gray To Black

Alternate Names

Cleiophane, Marmatite, Zinc Blende

Gemstone Groups

Key Separations

SR nature, magnification, cleavage, spectrum, very strong dispersion, SG and possible fluorescence.

Comments

Cleiophane can range from nearly colorless and pale yellow to light green. Marmatite is the black variety usually found in Marmato, Italy. Ruby Blende is the red variety of sphalerite. Stones are rarely chatoyant.

Sphalerite Optical Properties

Transparency

Transparent - Opaque

Refractive Index

Over the Limit 2.369-2.5

Birefringence

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

Singly Refractive (SR)

Fluorescence

SWUV: Inert to strong orange-red
LWUV: Inert to strong orange-red

CCF Reaction

Pleochroism

None

Dispersion

Strength: extreme fire Value: 0.156

Comments

Sphalerite Chemistry & Crystallography

Chemical Name

zinc iron sulfide

Chemical Formula

(Zn,Fe)S

Synthesis

Crystal System

Cubic

Classification

Sulfide

Nature

Natural

Crystallinity

Crystalline

Comments

Sphalerite Characteristic Physical Properties

Hardness

3.5-4

Streak

Yellowish To Light Brown

Specific Gravity

3.9-4.1 Typical:4.05

Toughness

Poor

Inclusions

Sphalerite is frequently color zoned and has very strong dispersion.

Luster

Adamantine

Stability

Fracture

Conchoidal, Uneven

Cleavage

Perfect, in six directions

Comments

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