How Is Slate Formed?

Written by creatingyourspace on . Posted in Tile and Natural Stone

Whether it’s uniform, gray, and gauged from Vermont or wild, colorful, and uneven from India, all slate shares several very distinctive characteristics. Like marble, slate is metamorphic in nature, but it differs widely from marble in its looks, hardness, and porosity, all of which come from how it is formed.

Metamorphosed Shale

Like all metamorphic rocks, slate was once a different type of rock altogether. Shale, a sedimentary stone made of clay and volcanic ash, was formed layer by layer. This clay and ash mixture, along with small amounts of quartz, pyrite, and other minerals in the clay, eventually hardened together to form the very soft rock we call shale.

Over time, sections of shale that were subjected to intense amounts of heat and pressure began to change composition, eventually becoming the stone known as slate.

Present Layers

Because shale was formed in layers, the slate that later came from it stayed this way. Large blocks of slate cut from the ground can show the history of their layers within the stone itself. This is why so many types of slate from China, India, and Brazil are what is known as “ungauged”. When the tiles were being formed, they were very roughly split by hand. Slate splits very easily along these layers, which is why you may find tiles in one box that have as much as ½-inch difference in their thicknesses.

These layers are what give slate its ragged appearance. While the stone can be ground down, this becomes expensive because so many pieces of the top layers often break off, known as spalling.

Slate and Quartzite

There are a few types of stone that are labeled as slate, but that are actually another type of metamorphic stone known as quartzite. Like slate, these stones may be formed in layers, but instead of spalling and splitting in flakes, they appear to be sugary with a rough, glittery surface. Quartzite slates are formed from sandstone, or shale that has a large amount of quartz in it. Functionally, they act the same as slate, and can be used in the same way.

We are happy to help with any questions you may have about any of your flooring needs! Please let us know at Dolphin how we can help you.

Tags: ,

Trackback from your site.

Leave a comment