Moonstone Vs Opal — What's the Difference?


Moonstone is a sodium potassium aluminium silicate with the chemical formula (Na,K)AlSi3O8 and belongs to the feldspar group.
Opal is a hydrated amorphous form of silica; its water content may range from 3 to 21% by weight, but is usually between 6 and 10%.


Moonstone is composed of two feldspar species, orthoclase and albite. The two species are intermingled. Then, as the newly formed mineral cools, the intergrowth of orthoclase and albite separates into stacked, alternating layers.

Opal is a hydrated amorphous form of silica (SiO2·nH2O), It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt.

Cause of Color

Blue Moonstone is a gem from the feldspar group and is composed of layers of albite – potassium rich aluminium silicate and orthoclase – sodium rich aluminum silicate. The schiller is produced because of light interference caused by the light having to weave its way through the layers with slightly different optical properties. The adularescence is caused by scattered light passing through the exsolution lamellae that act as scattering centres, creating a bluish hue/ lustre.
Precious Opal - is opal which exhibits the phenomenon known as play of colour, which is produced by the diffraction of white light through a micro-structure of orderly arrayed spheres of silica.The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colors.

Types and colors:

Moonstones come in a variety of colors. The body color can range from colorless to gray, brown, yellow, green, or pink. The clarity ranges from transparent to translucent.
There are many different types of natural opals. There is black opal, white opal, crystal opal and jelly opal. There are other kinds - fire opal, hyalite, water opal, hydrophane and honey opal.

See also:
Types of Opal With Photos
Different Types and Colours of Moonstone