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Moonstone; the June Birthstone 

Moonstone is one of the three colorful stones used to celebrate the month of June in the gemstone world alongside pearls and alexandrite. This popular gemstone belongs to the feldspar group of minerals and is composed of orthoclase feldspar with a small amount of albite feldspar. It has a chemical formula of (Na,K)AlSi3O8, where Na and K represent the sodium and potassium ions that substitute for each other in the crystal structure.

Rough moonstones

Moonstone is known for its adularescence, a phenomenon where it exhibits a floating light effect or a shimmering glow that appears to move across the stone’s surface when it is viewed from different angles. This phenomenon is caused by light scattering between microscopic layers of albite and orthoclase within the crystal structure. The stone gets its name from its appearance, reminiscent of the moon’s soft glow.

Moonstone is typically translucent to semi-transparent and comes in a variety of colors, including white, gray, peach, green, and blue. The color variation is caused by the presence of trace elements such as iron, titanium, and copper. The most prized and popular variety of moonstones is the rainbow moonstone, which displays various colors, often including blue and iridescent flashes. Moonstone has a Mohs hardness of 6-6.5 and a specific gravity of 2.5-2.6.

How are moonstones formed? 

Moonstones are formed through a combination of magmatic and hydrothermal processes. The process begins with the crystallization of magma, which produces a variety of igneous rocks such as granite and pegmatite. During the cooling and solidification of the magma, feldspar minerals such as orthoclase and albite crystallize and form interlocking crystals within the rock.

A moonstone pendant

The formation of moonstone requires an additional process, known as exsolution, which occurs during the cooling of the feldspar crystals. Exsolution is a process where one mineral separates from another mineral within a crystal structure due to differences in chemical composition or temperature. In the case of moonstones, the orthoclase and albite feldspars separate into alternating layers, which causes light to scatter and produces the characteristic adularescence effect (

Moonstone is commonly used in jewelry, including rings, earrings, necklaces, and bracelets. Its soft, glowing luster and translucent appearance make it highly valued by gemstone enthusiasts and jewelry designers alike.

Additional facts and properties of moonstone:

Clarity: Moonstones are often included, meaning that they contain minor imperfections. However, inclusions can add to the beauty of moonstones and are not considered to be a flaw.

Cut rainbow moonstones

Cut: Moonstone is mainly cut in a cabochon shape, which allows the light to reflect off of the surface and create a shimmering effect.

Value: The value of a moonstone depends on the color, clarity, cut, and size of the stone. The most valuable moonstones are those with a strong blue sheen, few inclusions, and a cabochon cut.

Luster: Moonstone has a vitreous to pearly luster, which gives it a soft, glowing appearance. The luster is caused by light reflecting off the surfaces of the mineral’s internal structure.

Cleavage: Moonstones exhibit perfect cleavage in two directions, meaning that they can be easily split along these planes to form smooth, flat surfaces.

Isomorphism: Moonstones can exhibit isomorphism which means that they can have different chemical compositions while retaining the same crystal structure. This is because different elements can substitute for each other in the crystal lattice.

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