Moissanite or cubic zirconia: what you are actually choosing between

Both look like a clear, bright stone, both sparkle, and both are sold as alternatives to diamond. The pages in this shop use the words moissanite, cubic zirconia, zirconia and zircon, and it is fair to wonder whether any of that matters once a piece is on. It does, mostly in how the stone holds up to daily wear.

What each one is

Moissanite is silicon carbide. The moissanite used in jewellery is made in a lab: GIA lists it as lab grown, and the 2CT Moissanite Huggie Hoop Earrings page calls its stones lab-created. A 1997 article in GIA's journal Gems & Gemology described synthetic moissanite as a new diamond substitute.

Cubic zirconia, usually shortened to CZ, is also lab-created. GIA classes both as diamond simulants: stones that can look like diamond but don't share its chemical, physical or optical properties.

Zircon is a third thing, and the one that causes the confusion. It is a natural gemstone, and GIA says it is unfairly confused with cubic zirconia. Where a page here says zircon, it doesn't say whether it means natural zircon or cubic zirconia, so we won't guess on its behalf. GIA puts natural zircon at 6 to 7.5 on the Mohs scale, softer than either of the other two.

Hardness: how each stone takes daily wear

Gem hardness is measured on the Mohs scale, where diamond is 10. GIA puts moissanite at 9.25, the hardest of the diamond simulants, and describes its toughness as excellent. It puts CZ at 8.5, and says CZ scratches more easily than diamond. Its buyer's guide adds that colourless CZ has been shown to yellow over time and can be somewhat brittle.

What that means in practice depends on where the stone is. A ring stone meets desks, door handles, car keys and the edge of every bench. A tennis bracelet sits where your wrist meets every table. A stud earring or a pendant hardly touches anything. So hardness matters most on rings and bracelets, and least on earrings and pendants.

Sparkle and colour

Fire is the flash of rainbow colour you see when a stone moves. GIA says moissanite has more than twice the fire of diamond, and that in large sizes its extreme fire can make it look artificial. Whether that is a drawback is up to you. Some people buy moissanite for exactly that flash. GIA makes a similar point about CZ, whose broad flashes of colour some people also find artificial.

Moissanite is also doubly refractive, and GIA says that can make it look slightly fuzzy from some directions. On colour, GIA says synthetic moissanite is produced near-colourless but can have a slightly greenish or greyish hue.

Side by side

All of it is from GIA's pages listed at the end. GIA's summary is that no simulant is as hard as diamond, but some are hard and durable enough to serve as ring stones for everyday wear. Moissanite, at 9.25, is the closest of them to diamond's 10.

Why moissanite can pass a diamond tester

The moissanite tennis bracelet and stud earring pages say the stones pass a diamond tester. That is a statement about the tester, not a claim that the stone is diamond. A thermal diamond tester, or thermal probe, checks how the stone conducts heat. When the authors of that 1997 Gems & Gemology article examined synthetic moissanite, they found its thermal properties so close to diamond's that the thermal probes then on the market reacted to it as if it were diamond.

A gemmologist can still tell them apart. The article noted that moissanite can be readily separated from diamond by the doubled appearance of its facet junctions. So a moissanite reading as diamond on a thermal tester says nothing about it being diamond. That finding dates from 1997 and covers the thermal probes sold then. We sell these stones as moissanite.

What the pieces here are set in

At the time of writing, every moissanite piece in the shop names 925 sterling silver as its metal on its own page:

• Moissanite Tennis Bracelet: a continuous row of moissanite in solid 925 sterling silver. The size options on the page are 2.5mm or 4mm, each in 16, 17, 18 or 19cm.
• Moissanite Solitaire Ring: a six-prong solitaire in solid 925 sterling silver, in sizes 5, 6, 7, 8 and 9.
• Moissanite Stud Earrings: classic studs in solid 925 sterling silver.
• Moissanite Smile Stud Earrings: a curved "smile" design set with moissanite stones, in 925 sterling silver, in 0.6 or 0.96 carats total weight.
• Moissanite Silver Ring: a moissanite stone in an elegant geometric design, in 925 sterling silver.
• The 2CT Moissanite Huggie Hoop Earrings, in 925 sterling silver.

The pieces set with zirconia or cubic zirconia vary more, so read each page for the metal:

• Tennis Bracelet, 4mm Zirconia Sparkle in Rose Gold Plated Silver: 4mm zirconia stones on a 925 silver base with a rose gold plated finish, in 16 to 20cm.
• Solitaire Pendant Necklace: a cubic zirconia in a six-prong setting, in rose gold, silver or gold colour. The page's only word on materials is a "Gold plated" label, which doesn't fit the silver option, and it doesn't name the base metal.
• Bubble Initial Necklace: a letter covered in pavé cubic zirconia, in silver colour. Again, no metal named.

So which one?

• A ring or tennis bracelet you will wear every day: moissanite, for the hardness. These are the pieces that take the knocks.
• Studs, a pendant, or something for occasional wear: hardness matters less on these, and GIA describes CZ as very affordable. GIA also says colourless CZ has been shown to yellow over time.
• Sparkle above everything: moissanite, which GIA says has more than twice the fire of diamond. See it in daylight before deciding it is too much.
• A page that says only zircon: it hasn't told you which stone it is, so judge the piece on its metal and on how you will wear it, rather than on the stone's name.

Neither is a diamond, and nothing here is sold as one. When you choose, think about where the piece will be worn. Rings and bracelets get knocked about more than studs and pendants.