Petrographic testing and terminology of natural stone

For the technical description, testing and classification of natural stone, the European standards DIN EN 12407:2019-12 and DIN EN 12670:2019-12 apply. These two standards complement each other and establish a consistent basis for quality assurance, transparency and comparability within the natural stone sector.

DIN EN 12407 – Petrographic testing

DIN EN 12407 specifies the procedure for the petrographic examination of natural stone, excluding roofing slate. The stone is analysed both macroscopically with the unaided eye and microscopically to determine its mineralogical and textural characteristics.

Rock analysis using polarizing microscopy

In this examination a sample is analysed as a thin section under a polarising microscope. A thin section is a carefully polished slice of rock approximately 20 to 30 micrometres thick, mounted on a glass slide with synthetic resin. Polarised light passes through the natural stone and enables the individual minerals to be distinguished by their optical properties. Under plane polarised light characteristics such as colour, transparency and cleavage can be observed. With crossed polarisers additional features such as interference colours and twinning structures become visible. By combining these observations the constituent minerals can be identified and the rock type determined with precision.

These observations form the basis for classifying the rock. The identified minerals and their quantitative proportions are evaluated and assigned to the main groups igneous, sedimentary or metamorphic. This enables the rock to be clearly named and described in a scientifically correct manner.

Granite under the polarizing microscope

Polished thin sections

For rocks containing opaque minerals, such as ores, sulfides or metallic inclusions, polished thin sections are used. These allow examination under reflected light, making it possible to clearly identify even the opaque components.

Polished and conventional thin sections are often combined to provide a comprehensive view of the rock’s structure.

The standard specifies, among other aspects, the following:

• the production of thin sections,
• the staining of minerals,
• as well as the scoring for statistical evaluation.

X-ray fluorescence (XRF) analyses are also used for the supplementary classification of volcanites, for example in TAS diagrams.

DIN EN 12670 – Standardized terminology and classification

DIN EN 12670 defines the standardized terminology and classification of natural stones in Europe.

It specifies how rocks are to be scientifically named and described, independent of regional trade names or traditional designations.

According to this standard, natural stones are divided into three main groups:

• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks.

Furthermore, DIN EN 12670 specifies which characteristics must be included in the technical description and in commercial documentation.

This facilitates communication between manufacturers, suppliers, designers and clients, and provides clarity throughout all project stages, from selection to execution.

Legal binding force and references

The binding nature of this requirement is based on building law and CE marking (Construction Products Regulation).

In the field of natural stone, the application of these standards often arises indirectly from the EU Construction Products Regulation (EU) No. 305/2011 and the harmonisation of product standards, in particular:

• DIN EN 1469 (Natural stone cladding panels for facades).
• DIN EN 12057 / 12058 (Floor and stair coverings made of natural stone).
• DIN EN 1341 / 1342 / 1343 (natural stone slabs, paving stones, curbstones).

These product standards explicitly refer to DIN EN 12407 and DIN EN 12670 for the petrographic identification and classification of the natural stone used.

This means that if a product is tested or CE-marked according to one of these harmonised EN standards, the petrographic examination according to DIN EN 12407 and the terminology defined in DIN EN 12670 must be applied.

Further information

If you have any further questions or would like information specific to your project, please feel free to contact us at any time via our contact form or send us a message at mail@besco-gmbh.de. We will get back to you promptly.

More exciting content awaits you in upcoming posts from the INFO series: Natural stone testing.