Williamsite | Gemopedia

Williamsite is a semi-transparent to translucent variety of antigorite, a mineral in the serpentine group. Williamsite was named in honor of 19th century American mineral collector L.W. Williams, who first discovered it. With a range of green hues, its color has a marked resemblance to two more expensive gems, jade and chrysoprase, and is used as a simulant of both. Williamsite exhibits an oily luster when polished and often contains minor inclusions of chromite and magnetite.
Colors
Oil Green, Intense Green

Williamsite Classification

Common Name

Williamsite

Species

Williamsite

Variety

Colors

Oil Green, Intense Green

Alternate Names

Gemstone Groups

Serpentine

Key Separations

RI, magnification, spectrum, appearance and surface condition.

Comments

Williamsite Optical Properties

Transparency

Semitransparent - Translucent

Refractive Index

1.53-1.575

Birefringence

Optic Character

Biaxial

Optic Sign

Negative

Polariscope Reaction

Aggregate (AGG)

Fluorescence

SWUV: Inert
LWUV: Weak whitish-green

CCF Reaction

Pleochroism

Unobservable

Dispersion

Comments

Williamsite Chemistry & Crystallography

Chemical Name

hydrous magnesium iron phyllosilicate

Chemical Formula

(Mg,Fe)3Si2O5(OH)4

Synthesis

Crystal System

Monoclinic

Classification

Silicate

Nature

Natural

Crystallinity

Microcrystalline

Comments

Williamsite Characteristic Physical Properties

Hardness

4

Streak

White

Specific Gravity

2.51-2.63

Toughness

Poor

Inclusions

Williamsite is often included with black octahedral chromite or magnetite inclusions. Stones often shows scratches and poor polish due to low mohs hardness. .

Luster

Waxy

Stability

Fracture

Conchoidal, Splintery

Cleavage

Perfect, in one direction

Comments

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