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The certification protocol developed for the GeoPT proficiency testing programme was applied to the certification of Iceland Tholeiitic Basalt IAG BNA-1. Certified values for eight major element oxides and twenty-nine trace elements were reported together with fourteen indicative values. Metrological traceability was demonstrated in part by the excellent agreement between GeoPT assigned values and certified values for the established certified reference material BRP-1 (Basalt Ribeirão Preto), which was distributed for co-analysis with BNA-1 in Round 54 of the GeoPT programme. A comparison shows clear similarities, but some differences when the composition of BNA-1 was compared with values for USGS BIR-1 (Reykjavik Iceland Basalt), which originated from the same quarry near Reykjavik in Iceland. An assessment of quality factors for IAG BNA-1 shows that BNA-1 certified values are fully compatible with usage involving the assessment of data submitted by laboratories that routinely analyse silicate rocks to the GeoPT ‘research laboratory’ standard of performance.

The GeoPT certification protocol (Potts et al. 2019) has demonstrated how this proficiency testing scheme can be used to certify geological reference materials. This protocol includes a full assessment of compliance with ISO Guide 35:2017 (now replaced by ISO 33405:2024) and has been successfully applied to the certification of IAG GMN-1 Meissen Granite CRM (Potts et al. 2024) with certified values published for nine major element oxides and thirty-nine trace elements. The present work describes the second application of this certification protocol, this time to a tholeiitic basalt from Iceland (IAG BNA-1), collected from the same quarry as USGS BIR-1 (Reykjavik Iceland Basalt). In compliance with the protocol, the independently certified reference material, basalt BRP-1 (Basalt Ribeirão Preto) was selected for co-analysis with BNA-1 in Round 54 of the GeoPT proficiency testing programme to independently validate measurement results submitted by participating laboratories and so provide evidence of their competence to contribute to data distributions appropriate for a certification study. The present work evaluates the data collected in Rounds 54 (BNA-1) and 54A (BRP-1) of the GeoPT programme that were used to derive certified values for eight major and twenty-eight trace elements in IAG BNA-1.