Where Do You Find Clay?
Clay is a common mineral material and important natural resource composed primarily of fine-grained minerals. It has a variety of uses and properties that make it a vital substance. Knowing where to find deposits of clay is key for many industries and applications.
Clay is an essential component in the manufacture of a wide range of products, including bricks, pottery, ceramics, cement, and plastics. It is also a key ingredient in drilling fluids used in oil and gas well drilling. In agriculture, clay is an important part of soil, providing necessary nutrients for plant growth. Clays are also used in cosmetics, medicine, paper making, and more.
Clay deposits can be found in many regions worldwide. Locating quality clay sources and accessing clay deposits allows manufacturers, builders, artists, and others to utilize this versatile material. Understanding the geology of clay formation gives insight into where it can be found and mined. This overview will examine the major clay deposits and geological sources of this abundant natural resource.
Clay Deposits
There are two main types of clay deposits: primary and secondary. Primary clays form as residual deposits in soil and remain at the site of formation. These deposits typically form from the chemical weathering of rocks such as granite, basalt and shale, where feldspar minerals break down into kaolinite clay [1]. Primary kaolinite deposits are found in tropical and subtropical regions where chemical weathering is most intense. Major primary kaolinite deposits occur in the southeastern United States, Brazil, Australia, and Europe [2].
Secondary clay deposits form through erosion and transportation processes before being deposited in river deltas, lakes, oceans and other sedimentary environments. Secondary clays include smectite, illite and chlorite. Smectite forms in arid environments, illite forms in temperate environments, and chlorite forms from alteration of volcanic ash. Marine clays consist of stratified layers on ocean floors, while glacial clays accumulate from glacial activity [3]. With transportation, the purity and crystallinity of secondary clays is lower than primary residual clays.
Residual Clays
Residual clays are formed from the natural weathering and erosion of rocks, mainly granite, gneiss and pegmatite (Glendale). These clays remain nearby the parent rock from which they were derived (Infoplease). Residual clays are formed through the mechanical and chemical breakdown of feldspar and other minerals within the parent rock over long periods of time.
Residual clays can be found near outcrops of granite, gneiss and pegmatite. They often occur in tropical and subtropical regions where chemical weathering is more rapid and extensive. Significant deposits are found across the southeastern United States, Brazil, India and Western Africa (Glendale). Residual clays may also accumulate in depressions and valleys near the parent rock.
The main minerals in residual clays are kaolinite, halloysite and iron oxides. The purity and types of clays depend on the composition of the source rock and the extent of weathering. Less weathered clays maintain some original minerals while more intensely weathered clays contain mainly kaolinite.
Sedimentary Clays
Sedimentary clays are formed over long periods of time from the gradual chemical weathering of rocks like granite and feldspar or the settlement of particles carried by wind and water. As these particles settle, they accumulate in layers known as sedimentary deposits. One of the most common sedimentary clays is kaolinite, which is primarily composed of kaolin minerals and forms from the chemical weathering of aluminum silicate minerals like feldspar under acidic conditions. Kaolinite deposits are found across the world, often occurring in tropical rainforest areas with heavy rainfall that accelerates the chemical leaching process. Major kaolinite deposits are located in Brazil, Australia, India, and the southeastern United States. Other sedimentary clays like montmorillonite and illite also form from the gradual weathering and transportation of particles that eventually accumulate in layers. These types of clays can be found in many sedimentary basins globally.
Marine Clays
Marine clays are sedimentary clays that form from deposits of fine-grained particles carried to the ocean by rivers and streams. They accumulate in coastal areas, bays, estuaries, and shallow seas over geologic periods of time. According to the Wikipedia article on Marine Clay, these clays can be found in coastal regions around the world.
The formation of marine clays involves several steps. First, weathering and erosion breaks down rocks on land into fine clay and silt particles. Rivers and streams then transport these particles to the ocean. Once in the ocean, the particles settle out of suspension and accumulate on the seafloor. Over time, the weight of overlying sediments compresses the deposited clay into dense, cohesive marine clay deposits.
In addition to river sources, marine clays can also form from seafloor volcanoes spewing out fine ash that settles on the ocean bottom. Furthermore, the interactions between seawater and volcanic material can produce clay minerals that add to marine clay deposits.
Marine clays are found along present and ancient shorelines and continental shelves around the world. Extensive deposits occur off the east coast of North America and in the Gulf of Mexico. The Pacific Coast also hosts substantial marine clay formations. Other notable locations include the North Sea, the Mediterranean Sea, and offshore regions of China and Southeast Asia.
Glacial Clays
Glacial clays, also known as ‘boulder clays’ or ’till’, are deposits of primarily illite and montmorillonite clays found in areas that were once covered by massive, moving ice sheets or glaciers. As the glaciers moved across the landscape, the powerful forces eroded underlying bedrock and incorporated rock fragments of all sizes into the accumulating glacial sediments. This created unsorted heterogeneous mixtures of clay, silt, sand, gravel and larger rock fragments known as till or boulder clay [1].
Some of the largest and most significant deposits of glacial clay have been found in areas like British Columbia, Canada which was once completely covered in ice. Analysis of clays from this region found a high concentration of over 60 trace minerals and elements including magnesium, calcium, iron, silica and fulvic acid https://nayelle.com/glacial-clay-over-60-minerals/. Illite and montmorillonite clays give glacial clay unique properties and potential health benefits.
Glacial clays can typically be accessed where historic glacial activity has occurred. Some key locations include Canada, parts of the northern United States, Northern Europe, and Russia.
Volcanic Clays
Volcanic clays, also known as bentonites, form from the chemical alteration of volcanic ash in marine environments. The ash weathers over time into very fine clay particles made up of the clay mineral smectite. Prominent deposits are found in regions with active volcanism like the western United States, Japan, and Italy. The Milos island in Greece hosts one of the largest bentonite deposits, formed by underwater hydrothermal processes near volcanically active vents. Bentonite deposits often accumulate in layers interbedded between lava flows, tuff beds, and volcanic sediments. They can be found in ancient lake beds, marine basins, and estuaries where volcanic ash accumulated and altered to clay. Major bentonite deposits in the western U.S. are found in Wyoming, Montana, Texas, and California. The unique properties of swelling and water absorption make volcanic clays useful for a wide variety of industrial applications.
References:
Volcanic clays. (2010, February 20). Magma Cum Laude. https://blogs.agu.org/magmacumlaude/2010/02/20/volcanic-clays/
Volcanic clays from Pantelleria. (2021, July 6). Unurgent Argilla. https://www.unurgentargilla.com/blog/volcanic-clays-from-pantelleria
Other Sources
Clay can sometimes be found in some unconventional places as well. According to the Ceramic Arts Network, artists have used alternative clay sources such as mud from rivers, anthills, termite mounds, and mole hills to create pottery and sculptures. While these types of clays may require more processing to remove impurities, they demonstrate that usable clay can be gathered from the environment in small quantities if needed.
Another unique but less common source of clay includes deposits from volcanic eruptions and ashfalls. According to Where is Clay Found?, volcanic eruptions and ashfalls deposit ash and small particles that over time can lithify into clay minerals. However, these types of clays are generally less abundant than sedimentary or residual clay deposits.
Accessing Clay Deposits
Locating clay deposits to harvest clay legally can take some research and effort. Here are some tips for finding and accessing clay deposits in your area:
Check geological survey maps and data from your state or national geological surveys. These can indicate where clay deposits are located based on geological formations and soil types. For example, the United States Geological Survey provides data on the location of clay minerals across the country.
Search for information on commercial clay mining operations in your vicinity. Public information on mining permits and leases may provide clues as to where substantial clay deposits are located nearby.
Look for exposed river banks and road cuts where clay subsoil is visible. Surface clay exposures can indicate wider clay strata underground, especially near creek beds and flood plains.
Obtain permission from landowners before extracting any clay from private property. Clay collected from state or federal public lands may require a permit or license.
Start with small test digs first before extracting large quantities of clay. First determine if the clay quality and type is suitable for your needs before fully mining an area.
Research local laws and regulations around clay extraction. Some municipalities may prohibit or restrict collecting clay from public spaces like parks, roadways, and waterways.
Conclusion
Clay is an incredibly diverse and useful material that can be sourced from many locations around the world. As we’ve explored, the three main types of clay deposits are residual clays, sedimentary clays formed by the weathering of rock, and marine clays deposited in oceans and lakes. Clays also come from volcanic ash and glacial movement. Knowing the different sources of clay allows us to locate and utilize this resource more effectively. Clay’s unique properties make it invaluable for many industrial and agricultural applications.
In summary, by understanding where clay comes from, we gain insight into how it is created through natural processes. This gives us clues about where to find substantial clay deposits suitable for mining and harvesting. With careful sourcing and stewardship, the many types of clay can continue providing us with their essential benefits.
