What is natural slate?
The word “slate” is believed to come from the Old French word scalar.
Natural slate is formed from fine-grained sediments, such as mud or sometimes volcanic ash, that were deposited millions of years ago in layers called bedding. As the sediment pile thickened, the original open mud structure was compressed into mudstone or shale.
These rocks are easily divided into bedding planes and are called bedrock. However, the formation of shale requires further intense geological forces associated with mountain building, during which the minerals present in the original mudstone are transformed.
Some minerals, such as quartz grains, are flattened and elongated, while clay minerals are recrystallized as plate minerals: white mica and chlorite. The quartz minerals give the slate its strength and durability, while the platy minerals form cleavage planes that do not match the bedding planes, but allow the stone to be split into much thinner slabs suitable as roofing material. Differences in the original mudstone composition and the degree of metamorphism affect the quality of the slate thus produced.
Natural Slate Geology
- Slate is a metamorphic rock of sedimentary origin.
- It dates back to the Ordovician period (550 million years ago).
- Consists mainly of quartz, sericite and chlorite group minerals.
- Used as a building material since the ancient Egyptians.
- Its color depends on the mineral structure and the size of the mineral grains, which determine its composition.
Use of natural slate
Slate has a long tradition as a building material. Slate is a natural, aesthetically attractive stone. Its strength and excellent flexibility make it one of the most durable and versatile roofing materials. The beauty of slate lies in the fact that it is a natural resource whose natural form requires little alteration and offers a long-lasting, pollutant-resistant, fire-resistant, water-resistant material with a warmth and elegance that makes it stand out among materials.
Slate is mainly used:
- Roofing
- Cladding
- Flooring
- Decorative finish
What is the age of natural slate?
The age of slate varies with regional geology.
For example, the Ballachulish slate in Scotland was formed from sediments deposited about 700 million years ago and metamorphosed 500 million years ago, while the Spanish slate, from the Orense area, was formed from mud laid down more than 450 million years ago and metamorphosed 300 – 350 million years ago.