Moonstone

Moonstone is a feldspar, known for its glowing color resembling moonlight.
Can belong to different members of feldspar group especially orthoclase and oligoclase.
Moonstone has a unique style of colors known as adularescence.
Is an abundant and inexpensive gemstone, often displays in addition to its mysterious glow effect, a cats eye effect and the band of light may float upon movement of the stone.
Asterism is a form of four-rayed stars also exists but less common.
The more transparent it is, the more valuable it is.
Moonstones with bluish color are more in demand and valuable.

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Care should be taken as moonstone is sensitive to pressure and can crack or chip.

Varieties:
Cat's Eye Moonstone - exhibits chatoyancy
Rainbow Moonstone - moonstone with blue sheen color, may be referring to labradorite also
Star Moonstone - moonstone with asterism

Similar gems:
Moonstone may look like some opal varieties but is harder and the glow is characteristic.

Formula plagioclase feldspars: (Na,Ca)AL1-2Si3-2O8
orthoclase feldspar: KAlSi3O8
Color: white, colorless, blue, green, yellow, orange, brown, pink, purple, gray
Hardness 6-6,5
Refractive index 1,518-1,526
Transparent to translucent
Luster pearly
Mineral class: orthoclase, oligoclase
Orthoclase composition: 14,05% potassium; 9,69% aluminum; 30,27% silicon; 45,99% oxygen;
16,92% K2O; 18,32% Al2O3; 64,76% SiO2
Density orthoclase: 2,56
Plagioclase composition: 4,25% sodium; 7,40% calcium; 9,96% aluminum; 31,12% silicon; 47,27% oxygen; 5,72% Na2O; 10,36% CaO; 18,83% Al2O3; 66,57% SiO2
Density plagioclase: 2,61-2,76; average 2,68

Adularescence
Optical effect exhibited on certain minerals and gemstones where they display a ghost-like reflection with a bluish-white color emanating from surface, effect caused by anomalies in its structure or build up of water.
Minerals with adularescence: Opal and Moonstone

Asterism
An effect of some polished cabochons that cause a reflection like a star which moves when rotated.
Asterism is caused by dense inclusions of tiny fibers in the mineral.
Minerals with asterism: Ruby, Moonstone

Chatoyancy
Effect of cat's eye in minerals causing a white reflected band across the center of the mineral, almost exclusively in polished cabochons.
Minerals: Moonstone

Sources:
https://www.minerals.net/gemstone/moonstone_gemstone.aspx
https://www.mindat.org/min-2774.html
http://webmineral.com/data/Orthoclase.shtml#.XaiLAugzbvM

Other names: moon stone moonstone piatra lunii cat's eye cat eye rainbowmoonstone rainbow star moonstone starmoonstone piatra luni