Chapter 2508 — Customs Tariff Headings

2508.30.00Fire-clay

2508.40.00Other clays

2508.50.00Andalusite, kyanite and sillimanite

2508.60.00Mullite

2508.70.00Chamotte or dinas earths

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Products classified under Tariff item 25.08

Agricultural Bentonite Sealant

Coarse sodium bentonite pellets used as a sealant for pond liners and irrigation canals in agricultural applications. This product is unprocessed bentonite clay, not fabricated into setts or excluded products, and therefore falls under tariff item 2508.10.00.

Bentonite for Cat Litter Base

Granular sodium bentonite clay used as the absorbent core material for clumping cat litters, imported in bulk for further processing. This unprepared clay is classifiable under tariff item 2508.10.00 as bentonite, not as a final consumer preparation.

Calcined Bentonite Clay

Bentonite clay subjected to controlled calcining to enhance adsorption properties for foundry sand bonding. The heading explicitly allows calcined clay products, and this remains classifiable under tariff item 2508.10.00 as bentonite.

Calcium Bentonite Powder

Fine-ground calcium bentonite clay suitable for animal feed binders and soil amendments, retaining its natural colloidal properties. This product is classifiable under tariff item 2508.10.00 as bentonite, whether or not calcined, but excluding processed products.

Foundry Grade Bentonite

Selected bentonite with optimal montmorillonite content for green sand molding in metal casting foundries. As a raw, unexpanded clay, it precisely matches tariff item 2508.10.00 specifications in the clays hierarchy.

High-Swelling Bentonite for Drilling

Premium Wyoming sodium bentonite with high swelling capacity, supplied in bulk for preparing water-based drilling fluids in oilfield operations. Tariff item 2508.10.00 covers this unexpanded, raw bentonite clay explicitly.

Natural Sodium Bentonite Clay

A naturally occurring sodium-based bentonite clay mined from volcanic ash deposits, used primarily as a drilling mud additive in oil and gas exploration. It falls under tariff item 2508.10.00 as unprocessed bentonite clay.

Calcined Fire-Clay Powder

Calcined fire-clay powder is a high-alumina clay processed at elevated temperatures to enhance its heat resistance, making it suitable for refractory brick manufacturing. It falls under tariff item 2508.30.00 as fire-clay, a clay product not subjected to processing beyond calcination, which is permitted under Chapter 25 Note 1. The product is in a powdered form, consistent with the mechanical processes allowed for classification in this chapter.

Chamotte Fire-Clay

Chamotte fire-clay is pre-fired fire-clay crushed into granules, used in refractory castables for improved strength. It is classified under tariff item 2508.30.00 as fire-clay, as chamotte is a form of fire-clay that has been fired and crushed, processes permitted by Chapter 25 Note 1. The product is essential for glass furnace repairs and other high-temperature applications.

Dinas Fire-Clay Earth

Dinas fire-clay earth is a siliceous fire-clay used in high-temperature silica bricks for coke ovens. It is classified under tariff item 2508.30.00 as fire-clay, given its siliceous nature and low flux content. The product is not subjected to processing beyond crushing or grinding, aligning with Chapter 25 Note 1.

Fire-Clay for Ceramic Kilns

Fire-clay graded for ceramic kiln furniture is designed to withstand repeated firing cycles up to 1400°C. It is classified under tariff item 2508.30.00 as fire-clay, as it is not worked into specific shapes and is supplied in bulk. The product undergoes only mechanical processes like crushing or grinding, consistent with Chapter 25 Note 1.

Fire-Clay Grogs

Fire-clay grogs are crushed and screened particles of fired clay used as aggregate in refractory mixes. They are classified under tariff item 2508.30.00 as fire-clay, as grogs are a form of chamotte or dinas earths. The product is valued for thermal stability in castables and is processed only by crushing and screening.

High-Alumina Fire-Clay

High-alumina fire-clay contains over 40% Al2O3, ideal for severe thermal shock in steel plant refractories. It is classified under tariff item 2508.30.00 as fire-clay, as the product is not expanded or subjected to processing beyond mechanical means. The clay is supplied in bulk and used in refractory applications.

Micaceous Fire-Clay

Micaceous fire-clay is a blend of fire-clay with natural mica flakes, enhancing thermal insulation properties for use in lightweight kiln furniture and refractory applications. It is classified under this tariff item as fire-clay because the mica content does not alter the clay's fundamental character as a refractory material, and it has not been subjected to processing beyond washing, crushing, or grinding.

Plastic Fire-Clay Mass

Plastic fire-clay mass is wet-mixed fire-clay for ramming into furnace shapes before firing. It is classified under tariff item 2508.30.00 as fire-clay, as the product is not mixed with other substances beyond water, which is not considered a prohibited mixing. The product is suitable for on-site refractory work in steel ladles and incinerators.

Raw Fire-Clay Lumps

Raw fire-clay in lump form is unprocessed high-alumina clay mined for refractory applications like stove linings. It is classified under tariff item 2508.30.00 as fire-clay, as it is in a crude state and not subjected to any processing beyond mining. The product is distinct from expanded clays or other minerals.

Refractory Fire-Clay Granules

Refractory fire-clay granules (2-6mm) serve as skeletal material in castable refractories for ladles. They are classified under tariff item 2508.30.00 as fire-clay, as the granules are pre-calcined and crushed, processes permitted by Chapter 25 Note 1. The product is vital for metallurgy and is supplied in a granular form.

Activated Attapulgite Decolorizing Earth

Activated attapulgite clay, finely ground and treated to maximize its adsorption capacity, is used primarily in oil refining to strip color impurities and contaminants from petroleum products. It qualifies under tariff item 2508.40.00 as an 'other clay' that has undergone only mechanical or physical processing, not chemical alteration beyond activation.

Attapulgite Clay Granules

Granular attapulgite clay in its natural, non-expanded state, used as a suspension agent in pesticides and drilling fluids. It is a natural clay that has not been subjected to processing beyond crushing or grinding, aligning with the scope of heading 25.08.

Attapulgite Drilling Grade Clay

Fibrous attapulgite clay optimized for oil well drilling fluids, providing suspension properties. It is classified under tariff item 2508.40.00 as an 'other clay' in powdered or granular form for industrial use, not calcined or expanded.

Ball Clay for Ceramics

High-plasticity ball clay mined for use in fine porcelain and sanitaryware production. As a natural, unexpanded clay, it falls under 'other clays' in heading 25.08, not being a kaolin or fire clay.

Bentonite Clay Lumps

Natural bentonite clay in lump form, valued for its swelling properties in drilling muds, cat litter, and sealants. It is a natural clay that has not been expanded or processed beyond mechanical means, fitting the scope of 'other clays'.

Bentonite Clay Swellable Grade

Sodium montmorillonite bentonite clay with high swelling capacity, used in drilling muds and sealants. Tariff item 2508.40.00 covers this as an 'other clay', unexpanded and suitable for industrial applications like oilfield services.

Bentonite Fuller's Earth for Cosmetics

High-purity fuller's earth sourced from bentonite deposits, processed for use in facial masks and oil-absorbing cosmetics due to its natural clarifying properties. It falls under tariff item 2508.40.00 as an 'other clay' in a processed but uncalcined state, suitable for general adsorption uses.

Blue Ridge Ball Clay

Blue Ridge ball clay from Georgia deposits provides medium plasticity for tile bodies and engobes, with good suspension properties. It is a natural, uncalcined ball clay, falling under 'other clays'.

Calcined Kaolin Metakaolin

Partially calcined kaolin producing metakaolin for high-performance concrete with pozzolanic reaction. Tariff item 2508.40.00 includes calcined 'other clays' unless specifically chamotte; metakaolin qualifies as processed clay, though calcination may be a concern.

Carolina Ball Clay

Carolina ball clay from North Carolina is valued for electrical porcelain insulators due to its high fired strength and low electrical conductivity. It is uncalcined and natural, falling under 'other clays'.

Common Brick Clay

Surface-mined common clay suitable for traditional brick and tile production. It is raw and uncalcined, falling under 'other clays' as a natural clay not otherwise specified.

Common Brick Clay Raw

Unprocessed loamy clay suitable for manufacturing common bricks and tiles. Tariff item 2508.40.00 includes such 'other clays' in their natural state, not prepared for immediate refractory use, and not subjected to processing beyond washing or crushing.

Devon Ball Clay

Devon ball clay, sourced from England's Bovey Basin, offers superior casting slip performance and vitrification for bone china and electrical porcelain. It is a natural, uncalcined ball clay, falling under 'other clays'.

Diatomaceous Earth Decolorizing Grade

Calcined diatomite selected for decolorizing applications in sugar refining and beverage processing, acting as a filter aid with adsorptive properties. Although primarily siliceous, it is classified under tariff item 2508.40.00 when specifically processed as a decolorizing earth, not as a general filter aid.

Earthenware Clay Mix

Blended natural clays for low-fire earthenware pottery, not agglomerated or calcined. The blend remains under 'other clays' as it is a natural clay mixture not processed beyond mechanical means.

Earthenware Pottery Clay Body

Blended clay body for earthenware pottery production, containing kaolin, ball clay, and flint. Tariff item 2508.40.00 applies as an 'other clay' prepared but not fired, suitable for ceramic manufacturing, though blending may be considered processing beyond Chapter 25.

English China Clay Ball Clay Blend

This blend combines English ball clay with china clay for improved workability in translucent porcelain. It remains under 'other clays' if ball clay characteristics predominate and the blend is not calcined or agglomerated.

Fire Clay Powder

Refractory-grade fire clay ground into powder for brick manufacturing and high-temperature applications. It is not calcined into mullite or chamotte, so it remains under 'other clays' as a natural clay.

Florisil Magnesium Silicate Decolorizer

Synthetic magnesium silicate adsorbent similar to natural decolorizing earths, used in pharmaceutical purification and analytical chemistry for removing impurities. It is classified under tariff item 2508.40.00 when presented as a decolorizing earth, despite its synthetic origin, due to its functional equivalence.

Fuller's Earth Attapulgite

Absorbent attapulgite fuller's earth used for oil refining and cat litter bases. Tariff item 2508.40.00 classifies this as an 'other clay', representing natural mineral absorbents not calcined or expanded.

Fuller's Earth Bleaching Clay

Bentonite-based fuller's earth processed for use in edible oil refining, effectively removing color bodies, soaps, and gums through adsorption. It falls under tariff item 2508.40.00 as a natural clay with high montmorillonite content, processed only by mechanical means.

Kaolin Clay Powder

Finely ground kaolin clay, also known as china clay, used in ceramics, paper production, and as a filler in paints. It is a natural clay not specified elsewhere in the chapter, falling under 'other clays'.

Kentucky Ball Clay

Kentucky ball clay is a fine-grained, highly plastic sedimentary clay prized for its whiteness after firing and low shrinkage. It is a natural, uncalcined clay, falling under 'other clays'.

Montmorillonite Bleaching Earth

Acid-activated montmorillonite clay for vegetable oil bleaching, removing chlorophyll and carotenoids effectively. It is a core component of fuller's earth with a 2:1 layer silicate structure, classified under tariff item 2508.40.00 as an 'other clay' despite acid treatment.

OM4 Ball Clay

OM4 ball clay is a coarse, high-plasticity grade ideal for outdoor sculpture and architectural ceramics, offering robust green strength. It is a natural, uncalcined ball clay, falling under 'other clays'.

Sepiolite Clay Absorbent

Natural sepiolite clay in absorbent form for cat litter and industrial spills, not expanded. It is a fibrous clay distinct from meerschaum, falling under 'other clays'.

Sepiolite Fuller's Earth

Fibrous clay mineral sepiolite processed as fuller's earth for cat litter decolorization and industrial absorbents. Its high porosity and adsorption make it ideal for oil spill cleanup and purification, classified under tariff item 2508.40.00 as an 'other clay'.

Sepiolite Meerschaum Ore

Natural sepiolite clay mineral, known as meerschaum ore, used for pipes and absorbents. It falls under tariff item 2508.40.00 as an 'other clay', explicitly covered in heading 25.30 note but prioritized here if not polished or worked.

Tennessee No. 9 Ball Clay

Tennessee No. 9 ball clay is a premium-grade ball clay known for exceptional plasticity, casting properties, and fired color suitable for tableware and sanitaryware. It is a natural, uncalcined clay, falling under 'other clays'.

Zeolite Decolorizing Earth

Natural zeolite powder with a crystalline aluminosilicate structure used for decolorization in wastewater treatment and edible oil processing. Tariff item 2508.40.00 applies to its role as a decolorizing earth based on adsorptive properties, despite zeolite's distinct mineralogy.

Calcined Andalusite 55% Al2O3

Calcined andalusite with 55% alumina content, heat-treated to partially convert to mullite for improved thermal shock resistance. This product falls under tariff item 2508.50.00 as calcined andalusite, which is explicitly covered by the heading regardless of calcination.

Calcined Kyanite Powder

Calcined kyanite powder, heat-stabilized to prevent volume expansion during ceramic firing. As a calcined form of kyanite, it is explicitly included in tariff item 2508.50.00, which covers andalusite, kyanite and sillimanite whether or not calcined.

Indian Sillimanite Sand

Indian sillimanite sand, washed and dried to -100+200 mesh, sourced from beach sand deposits. This naturally concentrated sillimanite is covered by tariff item 2508.50.00, which includes sillimanite in its crude or processed state as long as processing is limited to washing, drying, or mechanical sizing.

Kyanite Flour -325 Mesh

Kyanite flour ground to -325 mesh (<44 microns), used as a filler in porcelain insulators and spark plugs. This ground kyanite is classified under tariff item 2508.50.00 as it has only been mechanically ground, which is permitted processing under Chapter 25 notes.

Mullite-Forming Kyanite Concentrate

Beneficiated kyanite concentrate with 99%+ purity, selected for optimal mullite formation during firing. This uncalcined kyanite has been processed by mechanical or physical methods only, placing it under tariff item 2508.50.00 per Chapter 25 definitions.

Raw Andalusite Ore

Raw andalusite ore consisting of natural crystals extracted from deposits, containing 55-60% alumina. This uncalcined andalusite is directly covered by tariff item 2508.50.00, which includes andalusite in its crude state without further processing.

Sillimanite Grain for Refractories

Sillimanite grains, crushed and sized for use in refractory castables and ramming mixes. This unprocessed sillimanite, valued for high alumina content, falls under tariff item 2508.50.00 as sillimanite in a crushed or ground state, which is permitted under Chapter 25.

South African Andalusite Lumps

South African andalusite lumps, sized 10-100mm, containing 58% Al2O3, from Namaqualand deposits. This natural uncalcined mineral is covered by tariff item 2508.50.00 as andalusite in its crude state, used in steel ladle refractories.

Bauxite-Derived Calcined Mullite

> Bauxite-derived calcined mullite is produced by calcining bauxite to form the mullite phase, a high-alumina refractory material. It is used in abrasive refractories and high-temperature applications. This product falls under tariff item 2508.60.00 as mullite, distinct from raw bauxite ores, and is not excluded by Chapter 25 notes.

Calcined Mullite Aggregate

> Calcined mullite aggregate consists of crushed and heat-treated mullite grains used as a raw material in high-temperature refractories and castables. The product is processed only by crushing and heat treatment, which is permitted under Chapter 25 notes. It is classified under tariff item 2508.60.00 as mullite.

Fused Mullite Grain 200 Mesh

> Fused mullite grain in 200 mesh size is produced by electrical fusion of alumina and silica, resulting in a high-purity mullite material. It is used in precision casting molds and advanced ceramics. Fusion is a mechanical/physical process that does not exclude it from Chapter 25, so it falls under tariff item 2508.60.00.

High Purity Mullite for Investment Casting

> High purity mullite for investment casting is specially graded to provide thermal stability and low thermal expansion in casting shells. It is a processed mullite earth used in industrial refractory applications. This product is classified under tariff item 2508.60.00 as mullite.