Moonstone

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Refractive Index : 1.526 – 1.518 (+0.010 – 0.010)

Optical Characteristic : DR, biaxial negative

Specific Gravity : 2.58 (+0.03 – 0.03)

Formula : KAISi3O8

Crystal System : Monoclinic

Variety/Species : Orthoclase feldspar

Species/Group : Feldspar group

Birefringence : 0.005 to 0.008

Dispersion : 0.012

Hardness : 6 to 6.5

Toughness : Poor

Ultrasonic : Never

Steam : Never

UV Long : Inert to weak

UV Short : Inert to weak

Pleochroism : None

Strength : N/A

Pleochroism Colors : None

Heat : May fracture

Acids : Avoid hydrofluoric acid

Light : Stable

Polish Luster : Vitreous

Fracture : Uneven to splintery

Fracture Luster : Vitreous to pearly

Clarity Type : N/A

Tones : N/A

Saturations : N/A

Cause of Color : Adularescence – scattering of light

Enhancements : Coating

Cleavage : Perfect and easy, 2 direction

Color Range : Colorless, white, green, orange, yellow, brown, pink, red gray, to nearly, black. Most often has a blue or bluish-violet sheen of adularescence (caused by fine albite crystals).

Transparency : Semitransparent to opaque

Phenomena : Adularescence, 4 ray star

Separations : Natural Moonstone from-
Milky chalcedony : appearance, polariscope reaction, RI, birefringence, cleavage, fracture

Identifying Characteristics and information
Centipede-like inclusions which are intersting stress cracks. Adularescence is due to diffraction of light as it hits thin, alternating layers of orthoclase and albite within the gem. Goethite inclusions (iron oxide) cause the pink to red coloration sometimes seen.

Spectral Data
Not diagnostic.

Trade Names and Misnomers
Adularia
Cat’s Eye Moonstone
Ceylon opal (M)
Moonstone
Star Moonstone

Tags: Adularia, Cat's Eye Moonstone, Ceylon opal, Monoclinic, Moonstone, Othoclase feldspar, Star Moonstone