Moonstone

Group: Feldspar Mineral class: Silicates Colour white, pale yellow Colouring substance: adularia Pleochroism: absent Mohs’ hardness: 6 - 6.5 Density: 2.5 - 2.7 Cleavage: perfect Fracture: irregular, conchoidal Crystal system: monoclinic, prisms Transparency: opaque Lustre: adularescence Fluorescence: weak: bluish, orange

The adularia, from the family of feldspar, is the mineral out of which this gemstone is made. Only gemstones with the phenomena of adularescence are considered Moonstones. This is a white or silver lustre, very similar to the lustre of the opal or the mother-of-pearl. In the Moonstone, this lustre resembles the white lustre of the moon and is due to the numerous inclusions of feldspar.

The most precious Moonstones (those with a bluish-grey shimmer) come from Sri Lanka. There are also deposits in India, Madagascar, Burma and Tanzania.

It is usually cut in circular or cabochon style. If cut in this last fashion, it is recommendable to keep the surface relatively flat, so that the adular shimmer can be best appreciated and is not interfered with by iridescence or external reflexes.

This gemstone can be confused with chalcedony or with crystal imitations.