The IDEX Polished Diamond Price Index is a composite price benchmark published by IDEX Online, a diamond and gemstone trading platform headquartered in Ramat Gan, Israel. Updated daily, the index aggregates actual transaction data reported through the IDEX marketplace to produce a rolling indicator of polished diamond values across a defined basket of qualities and sizes. It is one of the principal alternatives to the Rapaport Diamond Report in the trade's toolkit for price discovery and market analysis, and is regularly cited by dealers, analysts, and financial commentators seeking a transaction-derived measure of polished diamond market conditions.

Background and Purpose

The polished diamond market has historically lacked the transparent, centralised pricing infrastructure common to commodities such as gold or platinum. Prices are negotiated bilaterally, vary by geography and relationship, and are influenced by factors — cut quality, fluorescence, provenance — that resist easy standardisation. Into this environment, price indices serve a critical function: they provide a common reference point that allows participants to assess whether the market is rising, falling, or consolidating, independent of any single transaction.

IDEX Online launched its polished diamond index as part of a broader effort to bring greater transparency and data rigour to the diamond trade. Unlike list-price systems, which are compiled editorially and adjusted periodically by a publisher, the IDEX index is constructed from prices at which diamonds are actually offered and traded on the platform. This transaction-based methodology positions it as a more empirical measure of real market sentiment, though it is subject to the composition and volume of trades flowing through the IDEX system at any given time.

Methodology and Construction

The index tracks a weighted basket of polished diamonds spanning a range of sizes, colour grades, and clarity grades representative of mainstream commercial demand. The exact weighting methodology and basket composition have been refined over time, but the index is broadly designed to reflect the categories most actively traded in the international wholesale market — typically round brilliants in the D-to-M colour range and IF-to-SI2 clarity range, across sizes from approximately 0.30 carats to 3.00 carats and above.

Daily updates are derived from live asking prices and completed transactions on the IDEX platform, which connects thousands of diamond dealers, manufacturers, and buyers globally. Because the data reflects actual market activity rather than a single publisher's assessment, the index can respond more rapidly to intraday and week-on-week shifts in supply and demand. The index value is expressed as a single composite number, with movements reported in percentage terms to allow straightforward comparison across time periods.

IDEX also publishes segmented data — breaking out price movements by size category and quality tier — allowing users to identify divergences between, for example, the sub-one-carat commercial market and the larger, higher-colour investment-grade segment. This granularity is particularly useful for manufacturers and retailers whose inventory is concentrated in specific categories.

Relationship to the Rapaport Diamond Report

The Rapaport Diamond Report, published weekly by the Rapaport Group, has served as the dominant price reference in the polished diamond trade since 1978. Rapaport prices are list prices — aspirational benchmarks from which actual transaction prices are negotiated at a discount (expressed as a percentage "off Rap"). This system is deeply embedded in trade practice, particularly in the United States and among Antwerp and Mumbai dealers.

The IDEX index occupies a different conceptual position. Rather than providing a list price from which discounts are calculated, it offers a directional indicator: a single number that rises or falls to reflect aggregate market conditions. The two systems are therefore complementary rather than strictly competitive. A dealer might use Rapaport prices to anchor individual negotiations while consulting the IDEX index to understand whether the broader market has moved since the last Rapaport publication. Financial analysts and macroeconomic commentators, who have less use for per-stone list prices, often find the IDEX index more tractable as a time-series data point.

A further distinction lies in accessibility. The Rapaport Report is a subscription product with tiered pricing and trade-membership requirements. IDEX Online makes summary index data available more openly, which has contributed to its adoption in academic research, financial journalism, and investment analysis contexts where the Rapaport system's access model presents a barrier.

Use in Market Analysis and Investment Context

The IDEX Polished Diamond Price Index gained particular prominence during the polished diamond price cycle of 2020–2022, when pandemic-era demand shifts, supply chain disruptions, and the emergence of laboratory-grown diamonds as a significant market force produced unusually sharp price movements. During this period, the index was widely cited in trade press, financial media, and analyst reports as evidence of the market's volatility and subsequent correction.

For those approaching diamonds as an asset class — a practice that remains contested among gemmologists and financial advisers alike — the index provides one of the few publicly accessible time-series datasets against which to assess historical price performance. It has been used in academic papers examining diamond price dynamics, in commodity-adjacent investment research, and by diamond-backed financial products seeking a transparent reference rate.

It is important to note the index's limitations in an investment context. Polished diamonds are not fungible: two stones of nominally identical grading-report specifications may differ materially in cut quality, fluorescence behaviour, or visual appeal, and will command different prices in the market. The index, by aggregating across a basket, smooths over this heterogeneity. It is therefore a useful directional indicator but an imperfect proxy for the value of any specific stone. Investors and advisers should treat it as one data point among several rather than as a definitive valuation tool.

Laboratory-Grown Diamonds and Index Evolution

The rapid growth of the laboratory-grown diamond sector from approximately 2018 onwards has complicated the interpretation of polished diamond price indices generally. As laboratory-grown stones — chemically and physically identical to mined diamonds but produced by chemical vapour deposition (CVD) or high-pressure, high-temperature (HPHT) processes — have captured an increasing share of the melee and commercial-quality market, the price dynamics of natural polished diamonds have diverged sharply from those of their synthetic counterparts. The IDEX index, which tracks natural polished diamonds, has therefore become a more specific instrument: a measure of the natural diamond market rather than the diamond market as a whole. IDEX Online has responded to this by developing separate tracking for laboratory-grown diamond prices, acknowledging that the two markets, while related, are increasingly governed by distinct supply and demand dynamics.

In the Trade

Among professional diamond dealers, the IDEX index is viewed as a useful supplementary tool rather than a primary pricing authority. Its daily publication cadence and transaction-based methodology give it credibility as a real-time sentiment gauge, particularly in periods of rapid market movement when weekly list-price publications may lag actual conditions. Larger trading houses and diamond manufacturers with significant inventory exposure monitor the index alongside Rapaport data, rough diamond tender results from De Beers and Alrosa (now subject to significant geopolitical constraints following 2022 sanctions), and polished auction results from the major auction houses.

For smaller dealers and those newer to the trade, the index provides an accessible entry point into understanding market direction without requiring the full apparatus of Rapaport subscriptions and trade-floor relationships. Its presence in financial and general business media has also helped communicate diamond market conditions to a broader audience beyond the specialist trade.

Further Reading

• GIA Gems & Gemology — Polished Diamond Price Research
• GIA Diamond Market Reports