Hackmanite | Gemopedia

Discovered in Greenland in the late 1890's, hackmanite is named for Finnish geologist Victor Hackman. It is a rare occurrence to find gem-grade hackmanite; at best, most crystals are translucent. Hackmanite is the light pink to pale violet variety of sodalite. It is a particularly unusual gem because it exhibits a special optical property known as "tenebrescence," a type of reversible photochromism. This feature allows the gems to temporarily change color when exposed to different light forms. While hackmanite gems are usually pink to violet, the color quickly fades to gray or greenish-white in sunlight, and will slowly return to the original color after changing the light. Its tenebrescent property makes hackmanite a prized mineral for collectors.
Colors
Pink, Pale To Deep Violet Some White In Sunlight Others The Reverse

Hackmanite Classification

Common Name

Hackmanite

Species

Sodalite

Variety

Hackmanite

Colors

Pink, Pale To Deep Violet Some White In Sunlight Others The Reverse

Alternate Names

Gemstone Groups

Sodalite

Key Separations

RI, SG, appearance and possibly fluorescence

Comments

Most hackmanite will fade in sunlight while some Afghanistan and Burma material are creamy white and turn violet or pink-red while exposed to sunlight.

Hackmanite Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.483
Tolerance:(+0.004/-0.004)

Birefringence

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

Singly Refractive (SR)

Fluorescence

SWUV: Variable
LWUV: moderate to strong orange to yellowish orange

CCF Reaction

Pleochroism

None

Dispersion

Strength: moderate fire Value: 0.018

Comments

Hackmanite Chemistry & Crystallography

Chemical Name

chloric sodium aluminum silicate

Chemical Formula

Na8Al6Si6O24Cl2

Synthesis

Crystal System

Cubic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline to Aggregate

Comments

Hackmanite Characteristic Physical Properties

Hardness

5-6

Streak

White

Specific Gravity

2.15-2.4 Typical:2.25

Toughness

Poor

Inclusions

Hackmanite can contain small black inclusions.

Luster

Vitreous

Stability

Fracture

Uneven

Cleavage

Poor, in one direction

Comments

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