Moonstone

Hardness: 6-6.5 (Mohs scale); Color: Pinkish-orange with white specks, varying from light pink to deeper orange-red, often with a shimmering or iridescent quality (schiller or adularescence); Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Good in two directions (orthoclase cleavage) at nearly right angles (90 degrees); Specific Gravity: 2.55-2.63

Moonstone is a variety of the feldspar group mineral orthoclase. It forms in igneous and metamorphic rocks, particularly in pegmatites and granites, as it cools and solidifies from magma or when existing rocks undergo high temperatures and pressures. The adularescence is caused by the intergrowth of two different feldspar types, orthoclase and albite, which creates lamellar layers that diffract light and cause the characteristic glow. Geological age varies depending on the specific formation.

Primarily used as a gemstone in jewelry due to its unique optical effect (adularescence/schiller). It is often cut into cabochons to best display this phenomenon. Less commonly used in industrial applications, except as a component of other feldspar-rich rocks.

Moonstone has been valued for centuries and was particularly popular in the Art Nouveau period. It is considered a sacred stone in India, often associated with the moon and feminine energies. The most prized moonstones exhibit a strong blue adularescence over a relatively colorless background.

To identify moonstone in the field, look for a pearly or opalescent appearance, especially when rotated under light, which reveals the characteristic shimmering effect. Its hardness is sufficient to scratch glass but can be scratched by quartz. It typically has a somewhat translucent to opaque appearance. Common locations include Sri Lanka (historically the most significant source), India, Australia, Brazil, Madagascar, Mexico, Myanmar (Burma), and the USA (New Mexico, Virginia, Pennsylvania). For collectors, look for strong adularescence and good color saturation, especially if it's a blue flash.