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Opal vs Moonstone: Two White Stones, Two Different Kinds of Light

By Digital Towns Crystals · Last reviewed October 8, 2026

Short answer: precious opal shows play-of-color, separate patches of pure spectral color that jump and change as the stone tilts; moonstone shows adularescence, a single soft white to blue glow that seems to float under the surface. Opal is amorphous hydrated silica, lighter (specific gravity about 2.1) and sensitive to heat and sudden temperature changes. Moonstone is a feldspar, heavier (about 2.56 to 2.62), with two cleavage directions that make it chip-prone. Common opal and glass "opalite" are the usual sources of confusion.

Why do people mix up opal and moonstone?

In a jewelry case or a bowl of polished pieces, both read as milky, translucent stones with light moving inside them. The trade adds to the confusion. Milky white opal with weak color can look like moonstone; "rainbow moonstone" shows colored flashes that look opal-like; and pastel common opal in pink or green sits next to peach and green moonstone at about the same price. Then there is opalite, which Geology.com describes as a name used both for natural common opal and as a marketing term for man-made glass or plastic with an opal-like look, often sold without any disclosure of its man-made origin.

The two stones need different care, so the identification is worth getting right. The broader guides on opal and moonstone cover each stone on its own; this page is about telling them apart.

Opal and moonstone compared

Property Opal Moonstone
What it is Hydrated silica, SiO2·nH2O Feldspar: orthoclase with albite layers
Structure Amorphous, no crystal lattice Crystalline (orthoclase is monoclinic)
Mohs hardness 5.5 to 6.5 6 to 6.5
Specific gravity 1.98 to 2.25 2.56 to 2.62
Refractive index 1.37 to 1.47 1.518 to 1.526
Optical character Isotropic (singly refractive) Biaxial (doubly refractive)
Light effect Play-of-color: discrete spectral patches Adularescence: one billowing glow
Cause of effect Diffraction from stacked silica spheres Scattering between thin feldspar layers
Breakage Conchoidal fracture, no cleavage Two cleavage directions
Main care risk Heat, sudden temperature change, drying Knocks, ultrasonic and steam cleaners

Hardness, gravity and refractive index are from Minerals.net's opal and moonstone pages; optical character from webmineral's opal and orthoclase data.

Why does one flash colors and the other glow?

Opal: a diffraction grating made of silica balls

GIA explains that precious opal is built from sub-microscopic spheres stacked in a grid, and that light passing between them diffracts and breaks into spectral colors. Each orderly patch of spheres acts on its own, so the color comes in distinct patches: a green patch, a red patch, a blue one. Turn the stone and each patch switches color or goes dark independently. Common opal has the same chemistry without the orderly stacking, which is why GIA divides opal into precious, with play-of-color, and common, without it. A pink or green common opal shows no flashes at all, just body color.

Moonstone: light scattered between layers

Moonstone starts as a single feldspar that contains both orthoclase and albite. GIA describes how, as the mineral cools, the two separate into stacked, alternating layers, and light falling between those thin layers scatters to produce adularescence. Because the layers are parallel through the whole stone, the glow is one broad sheen that slides across the cabochon as you move it, rather than a mosaic of colors. Geology.com describes it as a soft glow that appears to float just below the surface.

"Rainbow moonstone" is the exception that causes most mix-ups. Minerals.net notes the name may also refer to labradorite, and its blue and colored flashes come from a different feldspar. The labradorite vs moonstone comparison covers that distinction.

Five tests to tell them apart

1. Watch the light move

Hold the stone under a single overhead bulb and rock it slowly. Several small patches of different, saturated colors that change independently: opal. One soft white, silver or blue band that glides across the dome as a whole: moonstone. If there is no effect at all, you may have common opal, a low-grade moonstone or glass.

2. Weigh it against its size

The gravity gap is large, about 20 percent. A 66 mm sphere has a volume of roughly 150 cubic centimeters, so it should weigh about 390 g in moonstone at 2.58 and only about 320 g in opal at 2.1. Porous Ethiopian hydrophane opal runs lighter still: Geology.com notes that hydrophane opals typically have a lower specific gravity than other opal because of their porosity.

3. Check edges and chips for cleavage

Moonstone has two cleavage directions, so chips on a rim or drill hole often show small flat, stepped surfaces. Geology.com warns that one impact against a hard object can cleave a moonstone in two. Opal has no cleavage; its chips are smooth, shell-shaped conchoidal scoops.

4. Use a polariscope

Opal is amorphous and singly refractive, so between crossed polarizers it stays dark as you rotate it (strain can cause some patchy light). Moonstone is doubly refractive and blinks light and dark four times per full turn. This is a quick, non-destructive test any gem show booth can do.

5. Look for a glass imitation's tells

Man-made "opalite" has an opalescent look but, as Geology.com points out, no play-of-color, and it is often sold without disclosure. Suspect it when the glow is identical in every piece of a lot, the color is perfectly even from edge to edge, and the price is far below either natural stone. Natural moonstone shows internal layering and small breaks along cleavage under a loupe; natural opal shows patchy color or traces of its host rock.

Where are they mined?

Opal forms from silica carried by water. GIA describes seasonal rains in Australia's outback soaking into rock, carrying dissolved silica down and leaving it in cracks and between layers as the water evaporated. Geology.com reports that as much as 95 percent of world opal production has come from Australia over the last century, with Ethiopia rising as the second major source since a 1994 discovery. Common opal comes from many places; Geology.com's tumbling article pictures pink opal from Peru.

For moonstone, Geology.com names Sri Lanka as the most important source of fine moonstone, with significant production in Brazil, Myanmar and India. GIA records that miners in southern India found a bright "parrot green" moonstone in 1997.

Which costs more, and how is each judged?

Precious opal is usually the more expensive stone, but both span a wide range. GIA's opal quality guide values play-of-color that is visible from every angle, and grades type (black, white, crystal), color, pattern and body tone. Common opal in pink, green or blue is priced as an ornamental stone and is often cheaper than good moonstone. For moonstone, GIA looks at bodycolor and the color and placement of the sheen: adularescence should sit centered on the top of the cabochon, and value drops when it is visible only from a narrow range of angles.

In crystal traditions, both are associated with the moon and intuition, and Minerals.net lists moonstone, with pearl, as a birthstone of June. Neither association changes how the stones are graded.

How should each one be cared for?

GIA's opal care guide warns that heat from intense light can cause fine fracture lines called crazing and that high heat or sudden temperature changes can crack opal; warm, soapy water is the only safe cleaner. GIA's moonstone care guide rates moonstone 6 to 6.5 with poor toughness, recommends warm soapy water, and says ultrasonic and steam cleaners are never recommended. In short: keep opal away from heat and sunny windows, and keep moonstone away from hard knocks.

Which should you buy?

  • For moving rainbow color, buy precious opal, and check the listing video for color from several angles.
  • For a soft, glowing white or peach sphere, buy moonstone; a sphere shows the sheen from more directions than a flat cut.
  • For pastel color on a budget, buy common opal such as pink or green opal, which has no play-of-color but takes a good polish.
  • For daily wear, neither is ideal; moonstone tolerates warmth better, but its cleavage makes it vulnerable to knocks.

Shopping opal and moonstone we stock

  • Peach Moonstone Sphere: 54 to 66 mm sizes; at 66 mm expect roughly 390 g if the weight is listed.
  • Polarity Moonstone Sphere: a sphere format that shows the sheen rolling as you turn it.
  • Rainbow Moonstone: free forms and a 3.5 inch wand; the colored flash is the labradorite-type feldspar described above.
  • Black Moonstone: palm stones and spheres from 35 mm to 66 mm, a dark bodycolor that makes the sheen stand out.
  • Welo (Ethiopia) Opal: precious opal with play-of-color; keep it dry, since hydrophane material absorbs water and can change in look while wet.
  • Green Opal: common opal as 75 to 80 mm spheres and free forms; no play-of-color, so judge it on color and polish.

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Opal and moonstone in stock

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Frequently asked questions

Is moonstone a type of opal?

No. Moonstone is a feldspar, a crystalline aluminum silicate made of orthoclase and albite layers. Opal is amorphous hydrated silica with no crystal structure. They look alike only because both are translucent and both show light moving inside the stone.

Is opalite the same as moonstone or opal?

The word is used two ways. It can mean natural common opal without play-of-color, but it is far more often a trade name for man-made glass. Glass opalite is neither opal nor moonstone, and it shows a glow but never true play-of-color.

Which is harder, opal or moonstone?

They overlap. Opal runs 5.5 to 6.5 and moonstone 6 to 6.5 on the Mohs scale, so both scratch more easily than quartz. Moonstone's bigger weakness is cleavage; opal's is heat and drying.

Why is my moonstone showing colors like an opal?

It is probably "rainbow moonstone," a name that is often applied to clear labradorite-type feldspar rather than true orthoclase moonstone. Its blue and multicolored flashes come from layer spacing in that feldspar, not from the silica-sphere diffraction that makes opal flash.

Can opal and moonstone be cleaned the same way?

Yes, with warm soapy water and a soft cloth, which GIA recommends for both. Avoid ultrasonic and steam cleaners for both, and keep opal away from heat and sudden temperature swings.

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