Boulder Opal | Gemopedia

Known for its lively, flaming color displays, boulder opal is in high demand by collectors and jewelry designers. As opposed to cut opal gems, boulder opal features small opal veins running through its matrix. The precious opal's rainbow of colors make a dramatic contrast to the rich earthy reds and browns of the host rock, creating a one-of-a-kind display.
Alternate
Names
Precious Opal, Natural Opal Type 2, Yowah Opal
Colors
Brown With Seams Of Play-Of-Color

Boulder Opal Classification

Common Name

Boulder Opal

Species

Opal

Variety

Boulder Opal

Colors

Brown With Seams Of Play-Of-Color

Alternate Names

Precious Opal, Natural Opal Type 2, Yowah Opal

Gemstone Groups

Key Separations

Appearance, RI and fluorescence

Comments

Yowah opal is a boulder matrix opal that is cut to display the small seams mixed through out the ironstone.

Boulder Opal Optical Properties

Transparency

Transparent - Opaque

Refractive Index

1.45
Tolerance:(+0.020/-0.080)

Birefringence

Optic Character

NA

Optic Sign

Polariscope Reaction

Singly Refractive (SR) With ADR

Fluorescence

SWUV: Variable
LWUV: Variable

CCF Reaction

Pleochroism

None

Dispersion

Strength: none

Comments

Boulder Opal Chemistry & Crystallography

Chemical Name

hydrated silicon dioxide

Chemical Formula

SiO2-nH2O

Synthesis

Crystal System

NA

Classification

Silicate

Nature

Natural

Crystallinity

Amorphous

Comments

Boulder Opal Characteristic Physical Properties

Hardness

5-6.5

Streak

Specific Gravity

1.98-2.25

Toughness

Varies

Inclusions

Boulder opal will have seams of precious opal in brown ironstone, quartzite, rhyolite or basalt host rock.

Luster

Vitreous

Stability

Fracture

Conchoidal, Uneven

Cleavage

None

Comments

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