Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of natrolite–phonolite obtained from volcanic rock from Kaiserstuhl as a technological additive (functional group: anticaking) for all animal species. According to the conventional risk assessment, due to the lack of adequate data, the Panel is not in a position to conclude on the safety of the additive for the target species under the proposed conditions of use. However, from the tolerance studies in cattle for fattening and weaned piglets, effects observed in animal performance and blood clinical biochemistry suggest adverse effects on the animals supplemented with the additive. Based on current knowledge, there is no indication of substantial absorption of the components of the additive and, therefore, of concern for the consumer. The FEEDAP Panel is not in the position to conclude on the potential of the additive to be a skin and eye irritant. The additive is considered a respiratory and dermal sensitiser. In the absence of suitable data, the presence of small/nanoparticles cannot be excluded. As no suitable data in line with the requirements of the Guidance on risk assessment of nanomaterials were provided by the applicant, the potential risks associated with the presence of nanoparticles for the target species, the consumer and the user could not be assessed. Due to the lack of sufficient data, the Panel is not in a position to conclude on the efficacy of the additive.