Opal or Moonstone? How to Tell Them Apart
Opal knowledge · Comparison
Two stones that shimmer and are still fundamentally different
Opal or moonstone, almost everyone standing in front of both for the first time asks this. Both shimmer, both seem mysterious, both are pale. And yet they are not related: one is solidified silica gel with water, the other a feldspar. How to tell them apart is below, and which one is better for what.
The difference in one sentence: The moonstone shows a single, mostly bluish white shimmer that drifts across the stone like a cloud. The opal shows many colours at once, which travel and change as you tilt it.
How do you spot the difference fastest?
Tilt the stone slowly in the light and watch for one thing only: How many colours do you see at once?
A single shimmer, mostly bluish or white, gliding across the surface like a wave. It moves, but it does not change colour. The technical term for this effect is adularescence.
Several colours side by side, often in patches or bands: green next to blue, and a flash of red beside it. They change as you tilt it. This is called play of colour.
How do the two compare directly?
| Opal | Moonstone | |
|---|---|---|
| Mineral group | amorphous silica gel with water content | feldspar (adularia) |
| Optical effect | play of colour, multicoloured | adularescence, single coloured shimmer |
| Hardness (Mohs) | 5.5 to 6.5 | 6 to 6.5 |
| Typical colour | all of them, depending on the stone | white to grey, bluish shimmer |
| Birthstone | October | June |
| Special feature | every stone is unique | shimmer only visible from a certain angle |
Why do they shimmer so differently?
Both effects are created by light, but in different ways.
With the opal
Tiny silica gel spheres lie in a regular lattice. Light is diffracted by them and split into its colours, much as it is by a CD. The size of the spheres determines the colour.
With the moonstone
Two kinds of feldspar are intergrown in fine layers. Light is scattered at these layers, which creates the soft, cloudy shimmer.
How the opal's play of colour works in detail is covered at length in the article on the play of colour of the opal.
Which one takes more punishment?
There is little between them in hardness. The practical difference lies elsewhere.
Opal
Contains water and dislikes sharp changes in temperature. In return it is less sensitive to pressure from one direction.
Moonstone
Has pronounced cleavage. A hard knock can split it along these internal planes, even though it is not soft as such.
The same applies to both: protect from chemicals, store separately, take off for rough work. The rules are in our opal care.
Which one suits you?
Choose the moonstone if
you like it calm and single coloured, prefer a soft shimmer and want the stone to hold back.
Choose the opal if
you want colour, are looking for something one of a kind and want a stone that looks different in every light.
We carry genuine opals only. If you want to go the multicoloured route: pale opal and crystal opal comes closest to the moonstone visually, blue opal hits the cool tone. The full range is under opal jewellery.
The test you can do yourself
Hold the stone under a single point of light and tilt it slowly. If you see separate, clearly bounded patches of colour that jump, you have an opal in front of you. If you see a soft blue veil drifting across the whole surface, it is a moonstone. The difference is obvious the moment you have seen the two side by side.
Which one should you choose, case by case?
The table tells the stones apart. The buying situation decides which one you take home. Below are five situations in which mixing them up becomes expensive or annoying.
Engagement ring
Both stones are softer than sapphire. Opal has no cleavage, moonstone does. A blow along the cleavage plane can split moonstone. Opal breaks with a conchoidal fracture, often at the dome. Take care with an open prong setting; in a bezel, opal is fine for everyday wear. If you want colour and a one-of-a-kind piece, choose opal in a surrounding setting. If you want a calm sheen and less of a talking point, choose moonstone, also protected. Diamond remains the more robust engagement stone; that is not a judgment of taste, but a matter of Mohs hardness and cleavage.
Everyday necklace
Here the stone you want to look at wins. Opal changes in window light, in the office, under a spotlight in the evening. Moonstone keeps the same milky glow. If the wearer wants understated jewellery, moonstone is the more honest choice. If she enjoys compliments, opal is the right one.
A gift without asking
A light opal in silver suits more wardrobes than a large moonstone cabochon, which tends to be read as "esoteric", even if that is unfair. Moonstone works if the person already wears calm silver jewellery. Opal works if she wears colour at her ears or neck. Leave out the ring size in both cases.
Budget under 200 euros
In this range, good moonstone is easier to find than good precious opal. Cheap opal in this bracket is often a doublet, a triplet or a hydrophane Welo without explanation. Better an honest moonstone or a small light solid opal with documentation than a big fire with no origin.
Photo versus in person
Moonstone is easier to photograph because its sheen is flat. Opal dies in phone photos, especially crystal opal. If you buy online, you need several tilted shots under a point light for opal. For moonstone, one shot against the light that shows the glow is enough. If that is missing, the moonstone is often dead and the opal often undersold.
Metal: silver lifts cool moonstone and light opal. Yellow gold warms fire opal and dark opals, while on moonstone it quickly looks vintage. Care is similar; the difference is water and cleavage. Protect hydrophane Welo from chlorine and long soaks in particular, especially when it is not in a protective setting. It can still be worn as a ring. Moonstone does not like knocks on its cleavage plane. Neither belongs in an ultrasonic cleaner.
Birthstone: moonstone shares June with pearl, opal shares October with tourmaline. A June gift with opal is not a mistake, just a different story. Neither is an October gift with moonstone. If the person wants the stone as a birthstone, take the month seriously. If they want it as jewellery, trust your eye.
Earrings: a pair of moonstones is easier to match, because the sheen looks alike. A pair of opals has to be searched for. That is why an opal pair often costs more than the sum of two single stones. If you are giving earrings and have the budget, you are less likely to go wrong with moonstone. If you are giving a one-of-a-kind piece, choose an opal necklace instead of a forced pair. Hydrophane opal and moonstone in the same bath: the opal changes, the moonstone does not. That is the quickest practical test, but not one you should try with an expensive stone.
The test you can do yourself
Hold the stone under a point light source and tilt it slowly. If you see individual, clearly defined patches of colour that jump, you are looking at an opal. If you see a soft blue sheen that moves across the whole surface, it is a moonstone. You will notice the difference immediately once you have seen both side by side.
Common questions about opal and moonstone
What is the difference between opal and moonstone?
The opal shows several colours at once, which travel as you tilt it. The moonstone shows a single, mostly bluish white shimmer.
Is moonstone harder than opal?
Only slightly. Moonstone sits at 6 to 6.5 on the Mohs scale, opal at 5.5 to 6.5.
Which of the two is more valuable?
At the top end the opal, especially black opals with strong red. For simpler goods the two are closer together, and size, clarity and liveliness of the effect decide.
Can you mistake opal for moonstone?
A pale crystal opal and a moonstone can look alike at first glance. The test is simple: if the stone shows several changing colours as you tilt it, it is an opal.
Which month do they belong to as birthstones?
The moonstone is assigned to June, together with the pearl. The opal belongs to October, together with tourmaline.
Can you wear both together?
Yes, they do not clash visually. Just make sure they do not touch in the jewellery box, as both scratch easily.
If you are unsure or have questions, you are welcome to contact us at any time, even if you did not buy the opal from us. Contact form, email cs@libertyangels.de or call +49 171 1603048.
Verified authenticity
by Liberty Angels
Only natural, genuine opals. Each certificate is linked online to your order, so it is tamper-proof.
Written by Anton Kehler
Founder of FAERELLI & Liberty Angels
