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  • Writer's pictureKatherine Fortnum

Where Does Clay Come From?

Updated: Mar 6, 2022

Clay comes from the ground, usually in areas where streams or rivers once flowed.

It is made from minerals, plant life, and animals—all the ingredients of soil. Over time, water pressure breaks up the remains of flora, fauna, and minerals, pulverising them into fine particles. Larger particles are filtered out through rocks and sand, leaving silt to settle into beds of clay. How far silt travels from its source and how pure the silt is determines the type of clay it becomes.

Most clay minerals form where rocks are in contact with water, air, or steam.

Examples of these situations include weathering boulders on a hillside, sediments on sea or lake bottoms, deeply buried sediments containing pore water, and rocks in contact with water heated by magma (molten rock). All of these environments may cause the formation of clay minerals from pre-existing minerals.

Feldspar is one of the common clay-forming minerals; it comprises about 60% of the earth's crust!

There are 2 clay types -

Primary and secondary clay

Primary clay

If, during its creation, the clay stayed put and picked up no impurities, it will be mostly white (kaolin clay), this is considered primary clay. It is simply made up of alumina and silica and chemical water, making the purest, whitest clay.

Also known as residual clay.

Secondary clay

Secondary clay

The clay particles are made by decomposing feldspars that move from where they originally formed, by water in streams, rivers, and glaciers and they pick up impurities such as other minerals and organic substances, most of the pick up iron. They will have tan, brown, cream, or ruddy colours before and after being fired. The more iron in the clay, the darker it will be. Also known as sedimentary clay.

If you'd like to learn more about ceramics and the processes involved book onto one of my workshops and explore the exciting world of clay!

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