Brazilian Association Responds to Discussion of Metalutite

Technical Barriers and the Brazilian Slates in the European Market

Prepared by geologist Cid Chiodi Filho for the Minas Gerais Slate Miners Association – AMAR-MG

History of Technical Barriers

For the second time in the last 20 years, the marketing of Brazilian slates is being hampered by alleged technical barriers, primarily in the European roofing slate market. The first attempt, in 2007, was promoted by the Fundación Centro Tecnolóxico da Pizarra (Slate Technology Center Foundation), which proposed that Brazilian slates from Minas Gerais did not comply with standard EN12326 – Slate and stone products for discontinuous roofing and cladding.

However, after more in-depth geological studies in Brazil, the claims were subsequently overturned, as they demonstrated that the cleavage of Minas Gerais slates resulted from tectonic load overpressure. Resulting in the rock being considered true slates, with foliation defined as slaty cleavage, although not of the plane-axial type.

According to CUPA, what is often marketed in the UK and Ireland as “Brazilian slate” is actually “metallutite,” a rock considered weaker and less durable. It is alleged that, although similar in appearance, under real-world exposure and load conditions, its behavior differs significantly from that of true tectonic slate. The risks associated with Brazilian “metallutite” were exposed in a technical report published by the Cluster de Pizarra de Galicia (Spanish Association of Slate Producers).

Limitations of Geological Criteria for Regulation

It is important to emphasize that ancient geological processes cannot be reproduced or proven experimentally and, therefore, should not serve as a basis for the technological or commercial qualification of natural rock materials such as slates. Only technological characterization tests allow for the assessment of compliance with established regulatory standards. This is, in fact, the understanding expressed in the WTO Technical Barriers Agreement, which determines that technical regulations should preferably specify performance characteristics.

International Classification and Petrographic Characterization

Cárdenes et al. (2020)[1] proposed an International Classification of Roofing Slates (IRSC), including four rock groups: low-grade slate, s.s. slate, phyllites, and schists. Low-grade slate shares sedimentary and metamorphic characteristics, but the presence of slaty cleavage unequivocally places it in the metamorphic field. Therefore, Brazilian slate from Minas Gerais is classified as low-grade slate according to this criterion.

Detailed petrographic analyses of gray and black slates from the Minas Gerais region, conducted in France by the Laboratoire National de Métrologie et d’Essais (LNE) and CRIIT Materiaux Alsace, revealed that the microscopic texture of these rocks is lepidoblastic, indicative of “flow schistosity.” This texture reflects the alignment and organization of mineral grains, thus demonstrating their metamorphic character. Furthermore, the mineralogical paragenesis observed in these slates consists primarily of muscovite, quartz, and chlorite. The presence of these minerals, along with the schistose texture, confirms that Brazilian slates from Minas Gerais can be classified as metamorphic rocks, in accordance with the criteria of the EN12326-2:2000 standard.

The Complementary Role of Brazilian Slates

Brazilian slates complement the European market, including the Spanish market, allowing for better adaptation of dimension slate to market needs and roofing applications. It is not surprising that Spain itself and other traditional European slate producers are among the main export customers. Handled and installed correctly, Brazilian slate, is a credible, low cost alternative to other roofing products available on the European market.

Wilstshire based Roofing Merchant & Contractor AL King stock and fit Brazilian roofing slate. Used for many years extensively on both refurbishments & new build projects, they promote the use of hook fixing for Spanish, Brazilian & Fibre cement roofing slates, a practice they have been involved in since 1978.