Moonstone

They are a type of feldspar, which is the most common mineral on earth. so what makes them special?
First like most gemstones, they are crystalline.  But the gems consist of plates of two different types of feldspar, arranged alternately.  Light shining through the stone is refracted by these plates, to emerge as a striking glow, which shifts unexpectedly as the stone is moved.
The best moonstones are transparent blue.  However high quality stones are rare; many are translucent, with different colours.
The name comes from the old belief that the glow looks like moonlight.  In India they were believed to bring good dreams.  Moonstones are the birthstone for June.
Sunstones show a similar band of light, but the cause is completely different.

Treatments before purchase

I am not aware of any major dangers here.  Synthetic moonstone does exist, but is rare.

Caring for Moonstones

The stones are soft, and can be scratched by dust etc, so do not wear them when doing manual work.  They should not come in contact with any jewellery cleaner, but can be washed with lukewarm water.

Moonstone showing the plates which refract the light

The plates which refract the light are clearly visible in this picture. Note how they occur in two different planes. The dark patches are fracture planes. Click here for larger image (191KB). The white oval towards the top of the larger picture is the microscope light reflected from the surface of the stone. Normally I make sure this reflection is not visible, however when I moved the light so that its reflection was not visible, the plates also disappeared!

Moonstone with typical flaw

Detail of a high quality moonstone. This fracture is right at the edge so does not devalue the stone. Note the iridescence, also the plates which give the stone its distinctive appearance are just visible. This gem is actually blue but is mounted in gold, that's why it looks golden in this picture. Click here for larger image (197KB) - opens in new tab.

Martin Rees, Jeweller and Pawnbroker Home and Index Gemstones Contact us