Moonstone vs Opal : What’s the difference between Moonstone and Opal?

Rainbow Moonstone. Credit: gemsnjewelry 2014
Rainbow Moonstone. Credit: gemsnjewelry 2014

Moonstone vs Opal

Chemical Composition

Opal : (SiO2·nH2O)

Moonstone : ((Na,K)AlSi3O8)

About Moonstone vs Opal


Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content can range from 3 to 21 per cent by weight, but is usually between 6 and 10 per cent. Because of its amorphous nature, it is classified as mineraloid, unlike the crystalline forms of silica, which are classified as minerals.

It is deposited at a relatively low temperature and can occur in cracks of almost any kind of rock, most commonly found with limonite, sandstone, rhyolite, marl and basalt. Opal is Australia’s national gemstone.


Moonstone is a sodium potassium aluminum silicate ((Na, K)AlSi3O8) of the feldspar group with a pearly and opalescent schiller.

The most common moonstone is the orthoclase feldspar mineral adularia, named for the early mining site near Mt. Adular in Switzerland, now the town of St. Gotthard. Strong solution of plagioclase feldspar oligoclase + /-Potassium feldspar orthoclase also contains lunar stone samples.

Physical Properties

Opal is hardened by silica. Measures 7 on the Mohs hardness scale, with 10 being the hardest. Opal is available in a variety of colours, including white, red, pink and blue.

Moonstone is one of the most valuable forms of feldspar. Measure 6 on the Mohs scale. Moonstone ranges in color from silver gray to peach and has a white or blue sheen.


Opal occurs in a significant quantity and variety in central Mexico, where the Querétaro state mining and production center is located. In this area, the opal deposits are mainly located in the mountain ranges of three municipalities: Colón, Tequisquiapan and Ezequiel Montes.

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Spencer, Idaho, is another source of white opal base or creamy opal in the United States. A high percentage of opal contained exists in thin layers.

Other large deposits of precious opal can be found worldwide in the Czech Republic, Canada, Slovakia, Hungary, Turkey, Indonesia, Brazil (in Pedro II, Piauí), Honduras (more specifically in Erandique), Guatemala and Nicaragua.

Moonstone is the Florida State Gemstone; it was designated as such in 1970 to commemorate the Moon landings, which took off from Kennedy Space Center. Despite it being the Florida State Gemstone, it does not naturally occur in the state.


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