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.
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.
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!
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.
