Two jewellers quote you on what looks like the same diamond. One number is several thousand dollars higher. Neither explains why, and asking feels a little like accusing someone of something.
There is an explanation, and most of it has nothing to do with one stone being better. Diamond prices in Australia are assembled from a US dollar trade benchmark, a freight and tax layer, a set of weight thresholds that move the price without changing anything you can see, and a margin nobody itemises. Knowing which layer a quote is moving in tells you what you are actually comparing.
We design and make rings for a living, so there is an obvious conflict of interest in anything we write about pricing. Take what follows with that in mind — and notice what is missing. You will not find a price-per-carat figure below, because the places that publish those figures are almost all selling the stone attached to them.
Nearly Every Diamond You Are Quoted On Arrived Here Priced in US Dollars
Australia stopped being a meaningful source of gem diamonds when Rio Tinto's Argyle mine in the east Kimberley ceased mining on 3 November 2020, after 37 years and more than 865 million carats. Argyle was the world's largest producer of coloured diamonds and, in Rio Tinto's own words, virtually the sole source of rare pink diamonds. Its closure did not change what a white diamond costs in Sydney, because Argyle was never where Australian engagement ring diamonds came from. People assume a mining country has a domestic diamond price. It does not.
The stone is cut overseas, listed on an international trading network, and priced in US dollars. The exchange rate on the day your jeweller buys it is a real input into your quote, and the one input neither of you controls. A figure quoted on the same stone six weeks ago is not the figure today, and that is nobody moving the goalposts.
The Trade's Benchmark Is an Asking Price, Not a Price
The reference almost every diamond dealer in the world works against is the Rapaport Diamond Price List, which Rapaport describes as the international benchmark used by dealers to establish diamond prices in all the major markets. It is published weekly, every Thursday at midnight New York time, and all prices on it are in US dollars.
Two things about that list matter more than the list itself.
It is not a record of what anything sold for. Rapaport states that the list reflects high cash asking prices for well-cut, white diamonds, and that it is not a record of actual transaction prices but a benchmark reflecting seller asking prices in cash deals — no terms, no returns.
Real stones trade at a discount to it. Rapaport's own figure is that most diamonds trade 10–30% below list. That spread is where the trade lives, and it is wide enough that the phrase priced off Rap tells you almost nothing by itself. A stone bought at 35% back from list and one bought at 8% back can both be described, accurately, as priced against the same benchmark.
The list covers only rounds and pears, from 0.01 to 10.99 carats, with the pear list serving as the benchmark for other fancy shapes. Every emerald cut, oval, marquise and cushion in the country is priced by inference from a shape it is not.
It also describes natural diamonds only. Laboratory-grown stones run on a different mechanism and a very different trajectory — independent industry analyst Edahn Golan put wholesale lab-grown prices down 96% since July 2018, and down 13% year on year in the second quarter of 2026. A discount-to-benchmark frame does not transfer. That is a separate argument and we have already had it at length.
What Diamond Prices in Australia Carry Before Anyone Adds a Margin
Two government-set lines sit between the overseas asking price and the number on your quote, and neither is negotiable.
The first is duty, and its shape surprises people. Under the Australian customs tariff, loose diamonds — heading 7102, whether or not worked, but not mounted or set — carry a general rate of Free. Finished jewellery of precious metal, heading 7113, carries a general rate of 5%. A stone brought in loose and set into a ring here does not attract the duty the same stone attracts if it arrives already set.
The second is GST. The Australian Border Force applies it at 10% of the value of the taxable importation, and that value is not simply what the stone cost. It is the customs value, plus any duty payable, plus the amount paid to transport the goods to Australia and to insure them for that transport. Freight and insurance sit inside the base the 10% is calculated on.
None of this argues for or against buying anywhere in particular. It is the reason an overseas asking price and an Australian delivered price are not the same kind of number, and setting them side by side without adjusting compares a pre-tax figure to a delivered one.
Magic Sizes Explain the Jumps You Cannot See
Diamond prices do not climb smoothly with weight. GIA's term for the thresholds is magic sizes: boundaries at which, in GIA's words, the price per carat increases significantly. GIA places them at 0.25, 0.50, 0.75 and 1.00 carats. The International Gem Society lists a different set — 0.90, 1.00, 1.50, 2.00, 3.00, 4.00 and 5.00 carats — and describes prices as increasing exponentially rather than incrementally. That the two do not agree is itself useful. These are market conventions, not physics.
The effect at a boundary is severe. GIA's own comparison of a 0.96ct diamond against a 1.02ct diamond of otherwise identical grades puts the difference at as much as 20% more, for a size difference GIA calls almost imperceptible.
Which makes the rounding rule worth knowing. GIA weighs to the fifth decimal place and rounds up to the next hundredth only if there is a nine in the thousandth place: 1.769ct becomes 1.77ct, but 1.768ct becomes 1.76ct. A hundredth of a carat no eye will ever resolve can carry a stone across a threshold.
There is a trap on the other side of that. The International Gem Society warns that cutters will sometimes sacrifice cut to push an otherwise 0.98 or 0.99 carat stone into the higher bracket. The premium you pay for the round number can be funded out of the one property that makes a diamond look like something. The long version of why two stones with matching paperwork can look nothing alike is here.
The Questions That Tell You More Than the Number
A quote is one figure standing in for four or five separate decisions. These are the ones worth pulling apart.
- What discount to list is this stone priced at? Anyone buying in the trade knows without looking it up. A jeweller who cannot give you a figure either is not buying the stone themselves or would rather you had not asked.
- Is the weight sitting just over a threshold? If it is, ask what the equivalent stone just under would cost, and look at the two together. The difference in appearance is frequently nothing. The difference in price is not.
- What is in this figure besides the stone? Metal, labour, setting, design time and the cost of keeping a workshop open are all in there somewhere. Ask which of them move if the design changes.
- What would you change if the budget were fixed and the stone were not? This tells you how a jeweller thinks — whether they spend a client's money on the grades printed on a report or on what the ring looks like on a hand.
Here is the part that costs us something to write. Most of the gap between two quotes on the same specification is not the stone at all. It is the cost of the business doing the quoting: the premises, the people, the hours spent on designs that never get made. No jeweller itemises that, ourselves included, and it is the largest unexplained variable in any comparison you will run.
Which leads somewhere uncomfortable. If the number is genuinely the only thing you are comparing, buy from whoever is cheapest. A diamond of a given weight, colour, clarity and cut grade is close to a commodity, and commodities should be bought on price. Pay above the cheapest figure only if you are getting something that figure does not describe — a stone chosen by eye rather than off a list, a design that took real time, people you can sit down with. If none of that is on offer, the premium buys you nothing.
We are jewellers, not financial advisers, and none of this is advice about what any stone will be worth later.
What This Means in Practice
Two questions account for most of what looks inexplicable about a quote: what the stone is priced at relative to the trade benchmark, and whether its weight is parked just over a magic size. The tax and freight layer explains much of the rest, and why an overseas figure and an Australian one are not comparable on their face.
What is left is the business itself, and no amount of reading settles that. You have to meet the people and look at the work. If what you want is our own starting figure rather than the mechanics behind everybody's, we have put it in writing rather than leaving it to be asked awkwardly across a table.
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Laher is a bespoke jewellery studio in Surry Hills, Sydney. We design and handcraft engagement rings and fine jewellery using Australian sapphires and unique coloured diamonds.