A to Z of Gemstones: M: Moonstone


Gemstone family: Feldspar

Crystal System: Monoclinic

Moh's scale of hardness: 6-6.5

Lustre: Vitreous

Birthstone: June

About: Moonstone is a phenomenal variety of the orthoclase species that belongs to the wide group of feldspars.  Moonstones are praised for their widely recognised phenomenon called adularescence which refers to the sheen created by the thin layers inside the stone that make the light scatter.  Moonstones come in white, peach, green, brown and grey and the most valuable ones are near-transparent with a strong blue sheen.  Moonstones are usually cut into cabochons, beads and sometimes faceted stones.

Origin: The main sources for moonstones are: Sri Lanka, India, Australia, Germany, Brazil, Myanmar, Madagascar and Mexico.

Use in jewellery: Moonstone’s lustre is vitreous; it rates 6-6.5 on the Mohs scale which makes it suitable for jewellery that has secure settings to protect the stone from scratching.

Treatments, synthetics and imitations: There are no known treatments for moonstones and it has not yet been synthesized in the lab.  Materials that are most commonly used to imitate moonstones are glass and plastic.