Prehnite | Gemopedia

Prehnite is the first gemstone named for a person. It was named in honor of Colonel Hendrik Von Prehn, the Dutch mineralogist credited with its discovery in the 1700's in South Africa. Also, prehnite was the first mineral to be named and described from South Africa, long before the country became an important source for precious gems, including diamond. Many specimens of this gem have an interesting luminous quality, with a vitreous to mother-of-pearl luster. With color ranging from pale green to a pale yellowish green and a hardness of 6 - 6.5, Prehnite is considered to be fairly sturdy and long wearing when set in jewelry.
Colors
Light Green To Yellowish Green, Gray, Rarely White

Prehnite Classification

Common Name

Prehnite

Species

Prehnite

Variety

Colors

Light Green To Yellowish Green, Gray, Rarely White

Alternate Names

Gemstone Groups

Key Separations

RI, birefringence, and spectrum. Might have to use birefringence blink method.

Comments

Prehnite Optical Properties

Transparency

Translucent

Refractive Index

1.616-1.649

Birefringence

0.02-0.033

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Unobservable

Dispersion

Comments

Prehnite Chemistry & Crystallography

Chemical Name

calcium aluminum silicate hydroxide

Chemical Formula

Ca2Al2Si3O10(OH)2

Synthesis

Crystal System

Orthorhombic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline to Aggregate

Comments

Prehnite Characteristic Physical Properties

Hardness

6-6.5

Streak

White

Specific Gravity

2.8-2.95 Typical:2.9

Toughness

Varies

Inclusions

Prehnite can contain epidote and copper inclusions.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal, Uneven

Cleavage

Good, in one direction, Poor, in one direction

Comments

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