How Is Slate Formed? Metamorphosis & More

How Is Slate Formed? Metamorphosis & More

Tabletops, work surfaces, landscaping, roofing and floors. These are just a handful of the many uses for high-quality slate in the modern world. But, where does it come from? Most of us know that slate comes from the ground, but the formation process is both complex and fascinating.

Slate formation is a slow process, taking millions of years to complete, and is dependent on a specific set of conditions. It is usually found in areas that have experienced tectonic activity, such as mountains, volcanoes and other areas of high pressure and heat.

Here at Honister Slate, we believe it is important to educate individuals as to the origins of their materials. Read on to discover our guide to slate formation.


Sedimentary Rocks

The first step in the process of slate formation is the build-up of sedimentary rocks. These rocks are formed from the aggregation of sediments, such as clay, silt, sand and even volcanic ash. Over time, these sediments become compacted and cemented together to form rock.

It is important to understand that this is an incredibly slow process. It takes hundreds of millions of years for sediments to gather and compact before the process of natural slate formation even begins.


Once the sedimentary rocks have been formed, they undergo the process of metamorphism. In other words, they change form as a result of external factors. In the case of slate, metamorphism occurs when the sedimentary rocks are subjected to high pressures and temperatures. This change in form is caused by the movement of tectonic plates, which creates a great deal of heat and pressure within the Earth’s crust.

Westmorland Green Slate

Here at Honister Slate Mine, our Westmorland Green Slate is particularly interesting, as it is made up of volcanic ash that was spread across the land following eruptions millions of years ago. The Borrowdale Volcanoes spread ash and lava across the central lake district, leading to the formation of our famous green slate. The colour of our Westmorland Green Slate comes from the magnesium chloride present in the ash!

Honister Slate Underground Mine Tours

Looking to learn a little more about the process of slate formation and mining? You’ve come to the right place. We’re passionate about educating individuals of all ages about the history of the lake district and its rich natural resources.

Whether you’re looking for educational activities, team-building days out or an adrenaline rush like no other, we’ve got something for everyone.

Get in touch with us to discuss your requirements. We’re always happy to help.

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