Paul Zimnisky Diamond Index — The Independent Diamond Price Benchmark
Paul Zimnisky Diamond Index — The Independent Diamond Price Benchmark
Publicly accessible index tracking rough and polished diamond prices, published by industry analyst Paul Zimnisky
The Paul Zimnisky Diamond Index, published by industry analyst Paul Zimnisky from his New York-based research practice, is the most widely cited independent diamond price benchmark in the financial and trade press. Unlike the producer-published indices issued by De Beers, Alrosa, and other rough-diamond producers — each of which is structured around its own catalogue of rough categories and is generally inaccessible to outside researchers — the Zimnisky index is publicly available, methodologically transparent, and aggregates pricing data across rough and polished diamond markets and across natural and laboratory-grown product categories. The index is updated regularly and has, over its decade-plus of publication, become the default reference for analysts, dealers, and financial-press writers needing a consistent diamond price series.
Methodology
Zimnisky's methodology aggregates data from multiple sources: published auction results, dealer transaction reporting, polished-price benchmarks (including Rapaport prices, where applicable, and the IDEX online polished diamond price list), and producer pricing data where it is publicly disclosed. The index is calculated as a weighted composite that tracks both rough-diamond prices (the trade between mining producers and cutting/polishing houses) and polished prices (the trade between cutting houses and the retail and dealer market). Separate sub-indices break out natural versus laboratory-grown diamonds, allowing users to track the two product categories independently and observe the divergence in their pricing over recent years.
Position in the market
The diamond industry has long been characterised by opaque pricing, with producer-controlled rough markets and a polished market historically organised around proprietary price guides (most prominently the Rapaport Diamond Report) that are commercial subscription products. Against that background, the Zimnisky index serves a useful function: it provides a publicly cited, methodologically explained reference series that financial analysts, trade journalists, and investors can use to discuss diamond market conditions without paywall or subscription barriers. The trade does not regard the Zimnisky index as a replacement for the proprietary catalogues used in actual transactions; it functions as a market-conditions benchmark rather than a transaction-pricing tool.
Natural versus laboratory-grown
One of the most consequential analytical contributions of the Zimnisky index has been its long-running tracking of laboratory-grown diamond prices alongside natural diamond prices. The index has documented the substantial wholesale price decline in laboratory-grown polished diamonds since the mid-2010s — from premiums comparable to natural diamonds to discounts of 60 to 90 per cent against natural equivalents in current data — and the corresponding pressure that decline has placed on the natural-diamond pricing structure. The series has been frequently cited in trade-press reporting on the divergence and in industry strategic analysis.
In the trade
For the practising jeweller and dealer, the Zimnisky index is most useful as context: it does not price individual stones (which depend on the 4Cs and on lab-report-specific factors that no aggregate index can capture), but it tracks the macro trends — rising or falling rough prices, polished market direction, the natural/laboratory-grown spread — that shape inventory strategy and investment positioning. Skyjems and other trade participants reference the index in market commentary and in conversations with clients about long-term trends, while pricing individual stones against the appropriate transaction-level benchmarks for each category. The index is regularly cited in Forbes, Bloomberg, Reuters, JCK, National Jeweler, and other financial and trade publications.