Ground or Treated Mineral and Earth Manufacturing (U.S.) — NAICS 327992

1. Overview

This industry takes rock that has already been dug out of the ground and turns it into engineered powders. Companies grind, classify by particle size, dry, calcine (heat-treat), expand, exfoliate, acid-activate, or surface-coat non-metallic minerals — limestone, barite, talc, mica, diatomite, perlite, vermiculite, feldspar, silica, graphite, bentonite, fuller's earth, and similar clays — so they can be sold as functional ingredients [1]. These powders rarely appear on a store shelf, but they are inside paint, plastics, rubber, paper, adhesives, caulk, drywall, drilling mud, cat litter, pool filters, edible-oil filtration, renewable-diesel purification, and food and pharma products. It is a business of turning cheap tonnage into graded, spec-controlled material.

Why an investor should care: this is a defensive, cash-generative "picks-and-shovels" corner of materials. Volumes track construction, autos, packaging, and oil-and-gas drilling, so it is cyclical — but the products are hard to substitute, the customer relationships are sticky, and the best assets are protected by geography rather than by patents. It is not a growth sector; it is a steady, freight-protected niche where owning the right deposit near the right market is the whole game.

Ways in differ sharply by investor type. For public-market investors there are essentially two meaningful U.S.-listed names (Minerals Technologies and Oil-Dri) plus one European-listed global leader (Imerys); the rest of the industry is private — family-owned, private-equity-held, or a division of a foreign parent. For private investors, that same fact is the opportunity: most of the attractive tonnage in America sits in businesses you can only reach by buying them.

2. What it is and how it's structured

NAICS 327992 covers establishments that process non-metallic minerals beyond beneficiation — that is, past the basic crushing and washing done at the mine — by calcining, dead-burning, grinding to a controlled fineness, expanding, exfoliating, acid-activating, or chemically treating them [1][2]. Typical outputs: ground and surface-treated calcium carbonate (from limestone or marble), ground barite, ground and milled talc, ground mica, processed diatomaceous earth (diatomite), expanded perlite, exfoliated vermiculite, activated bleaching clay, ground feldspar and silica, and ground or refined natural graphite [1].

The boundary matters: NAICS 327992 is an establishment classification, not a list of companies. A vertically integrated producer may report its quarry under mining, its calciner under 327992, and its consumer-product or refractory plant under another manufacturing code [2].

What it excludes matters for reading the statistics:

• The mining itself. Crushing, screening, and preliminary beneficiation at the quarry are classified in NAICS 2123 (Nonmetallic Mineral Mining and Quarrying) — including 212393 for barite and other chemical/fertilizer minerals and 212390 for miscellaneous non-metallics [1][2]. Most producers own both the mine and the grinding plant, so a single company reports across two codes.
• Precipitated calcium carbonate (PCC). PCC is made by a chemical reaction (limestone → lime → carbonation), so it is classified as chemical manufacturing (NAICS 325180), not here — even though it competes head-to-head with ground calcium carbonate. This is why the flagship U.S. company, Minerals Technologies, is only partly "in" this code.
• Lime (calcining limestone into quicklime/hydrated lime) is NAICS 327410; cement is 327310; crushed stone and construction aggregates are 327310/2123. Activated carbon and many chemical treatments fall under chemicals.

Ownership mix: a handful of global specialty-minerals majors (Imerys, Omya, Sibelco, Minerals Technologies, Huber, Carmeuse) sit on top of a long tail of regional grinders and single-mineral processors [3]. Federal data count 148 firms operating 275 establishments in the U.S. [4][5]. This is a genuine manufacturing industry — not one dominated by governments or by tiny sole proprietors — so the federal count is reasonably complete. The main reason the code understates the real economic activity is definitional: the mining tonnage lands in NAICS 2123, PCC lands in chemicals, and diversified minerals firms scatter their output across a dozen codes. The industry as a commercial reality is bigger than "275 plants and $6.4 billion" suggests.

3. How big it is

Federal figures (prefer these):

• Value of shipments / receipts: about $6.45 billion in 2022 [4].
• Establishments: 275 (2023) [5].
• Firms: 148 (2022) [4].
• Employment: 10,279 workers (2023) [5].
• Annual payroll: $875.4 million (2023), or roughly $85,000 per employee — well above the manufacturing average, reflecting a capital-intensive, low-headcount process business [5].
• SBA small-business size standard: up to 600 employees — a high threshold, meaning almost every firm in this industry counts as "small" by federal contracting rules [6].

Mineral-specific snapshots from USGS illustrate concentration and value dispersion within the industry:

• Diatomite: only six companies operating nine processing facilities produced U.S. diatomite in 2025; output was 720,000 metric tons valued at $420 million. Filtration represented approximately 60% of use. Prices ranged from roughly $10 per metric ton for lightweight aggregate to more than $1,000 per metric ton in specialty applications — illustrating why tonnage is a poor proxy for value [7].
• Perlite: six companies managed nine Western mining operations in 2025, while crude perlite was expanded at 53 plants in 29 states. Domestic processed-crude sales were 460,000 metric tons valued at $36 million; construction products represented 45% of expanded-perlite applications, horticultural aggregate and filter aids 15% each [8].
• Vermiculite: more concentrated upstream — two U.S. producers supplied concentrate in 2025, while ten companies operated 12 exfoliating plants [9].

For scale context from private market research (adjacent, not federal): the U.S. ground-plus-precipitated calcium carbonate market alone was estimated near $4.8 billion for 2025, and North America holds roughly 32% of the global mineral-fillers market [10][11]. Calcium carbonate is the single largest product line; talc, silica, and barite follow [11].

4. The investable universe

Public equity exposure to this niche is unusually thin. Reserve the tickers and prices below for the "how to invest" discussion; the point of the table is who owns the tonnage.

Adjacent listed names worth knowing but not pure plays: U.S. Lime & Minerals (NASDAQ: USLM) is mostly a lime producer (NAICS 327410) with some limestone products; Vulcan Materials (NYSE: VMC) and Martin Marietta (NYSE: MLM) are construction-aggregate miners, not mineral grinders. Bottom line: outside MTX, ODC, and Imerys, this industry is a private-ownership world.

5. How the money works

Owners make money on the spread between cheap mined rock and graded, spec-controlled powder, and on keeping freight low. The key levers:

• The value ladder. The same mineral sells across a huge price range depending on how finely it is milled, how bright/white it is, and whether it is surface-coated. Bulk "filler grade" is close to a commodity — priced at cost plus freight. Ultrafine, high-brightness, and surface-treated (coated) grades earn far higher margins because they let a customer, say, replace expensive titanium dioxide pigment with cheaper carbonate, or improve a plastic's stiffness and finish [11][19]. Moving up this ladder is the core margin story. The diatomite price range — from ~$10/tonne for lightweight aggregate to $1,000+/tonne for specialty grades — exemplifies the value dispersion [7].

• Freight is destiny. These are low value-to-weight products; shipping a $100–$200/tonne powder more than a few hundred miles can double its delivered cost. So plants are sited either on top of the deposit or next to the customer, pricing is regional ("delivered cost" competition), and a producer's real moat is often just being the closest quality source. USGS notes that transportation cost determines the maximum economic shipping distance against substitutes [7]. The extreme solution is Minerals Technologies' satellite PCC model: it builds and operates the mineral plant inside a paper mill under a ~10-year requirements contract, using the mill's land, power, and waste kiln gas, and eliminating transport entirely [20]. That structure — long-term, on-site, take-substantially-all-requirements — is why the specialty end of this business has stickier economics than a commodity grinder.

• Throughput, energy, and ore quality. Grinding, drying, and calcining are energy-intensive (natural gas plus electricity), so capacity utilization and energy cost swing margins directly. Oil-Dri's fiscal 2025 shipping and handling cost alone was $64.9 million, and the company identifies energy, transportation, packaging, maintenance materials, and labor as major cost risks [13]. Input cost is the mined ore, and ore quality (whiteness, purity, low grit) determines what grades a plant can make and its yield.

• Contract structure and cyclicality. Specialty grades (paper filler, personal-care, filtration) often run on multi-year contracts; commodity fillers and barite are more spot-priced and more cyclical. Barite is the most cyclical product in the industry: more than 90% of it goes into oil-and-gas drilling mud as a weighting agent, so barite grinders live and die by the rig count [21]. Consumer absorbents, food filtration, water treatment, and agricultural uses can offset construction, steel, paper, and drilling downturns — "cycle" is really a portfolio of unrelated mini-cycles rather than one macroeconomic beta [12].

Typical economics: specialty players run mid-teens operating margins and low-20s% EBITDA margins. Oil-Dri reported a 29.5% gross margin in fiscal 2025 [13]. Minerals Technologies reported company-wide production margin of 25.0% in 2025, with operating margins of 11.3% in Consumer & Specialties and 17.4% in Engineered Solutions [12]. Capital intensity is moderate — steady maintenance capex on mills and kilns plus periodic mine development — which makes the better operators reliable free-cash generators.

6. What drives demand

Demand is a bundle of end-markets, each pulling different minerals:

• Paint and coatings — carbonate, talc, mica, silica, and diatomite as extenders, flatting agents, and TiO₂ replacers. In 2025, 19% of U.S.-produced talc went to paint [22].
• Plastics and rubber — carbonate and talc as fillers/reinforcement (talc stiffens polypropylene for autos and appliances). 36% of U.S. talc sales went to plastics, 2% to rubber [22].
• Paper and packaging — carbonate as filler and coating; 12% of talc to paper [22]. Graphic-paper demand is in structural decline, but packaging and board demand is growing and partly offsets it [12].
• Construction — fillers in joint compound, sealants, adhesives, flooring, and roofing (8% of talc); perlite and vermiculite for lightweight aggregate and insulation (45% of expanded perlite goes to construction products) [8][22]; tied to housing and non-residential building.
• Oil and gas drilling — barite weighting agent; roughly 2.3 million tonnes sold by U.S. crushers and grinders in nine states in 2024 [21].
• Filtration and consumer — diatomite and perlite as filter aids for beer, wine, food, and pools (filtration is ~60% of diatomite use); bentonite and diatomite for cat litter and absorbents (a growing consumer/pet line) [7][12][16].
• Horticulture — perlite and vermiculite as growing media (15% of perlite use); some substitution from wood fiber and coco coir on cost, though perlite retains durability and inertness advantages [8][23].
• Renewable diesel and edible-oil purification — bleaching clay removes impurities from feedstocks; Oil-Dri attributed part of its fiscal 2025 B2B growth to purification products for renewable diesel, though changes in government incentives could alter that demand [13].
• Environmental — bentonite liners and waterproofing, wastewater remediation, drinking-water purification, spill absorbents, vapor barriers, and contaminant binding; a credible secular growth area [12][13].
• Agriculture, food, and pharma — mineral carriers, food-grade calcium carbonate, and filtration.

A structural tailwind across several of these is titanium-dioxide extension: fine carbonate and other minerals let formulators cut costly TiO₂ pigment, so demand grows whenever pigment prices rise [11][19]. An offsetting threat in filtration is membrane technology: ceramic, polymeric, carbon, and cellulose-based filters increasingly compete with mineral filter aids [7].

7. Regulation

• Worker dust exposure is the dominant regulatory theme. Respirable crystalline silica causes silicosis and lung cancer. OSHA's general-industry permissible exposure limit is 50 µg/m³ (action level 25 µg/m³), measured as an eight-hour time-weighted average; the general-industry rule contains a specific exception for silica exposure from processing sorptive clays [24]. In April 2024 the Mine Safety and Health Administration (MSHA) finalized a rule cutting the mine limit to the same 50 µg/m³ (action level 25 µg/m³), effective June 2024, with metal/non-metal mines phasing in compliance and medical surveillance through 2025–2026 [25]. Because most producers operate both a mine (MSHA) and a plant (OSHA), they sit under both regimes; jurisdiction can shift depending on whether the facility is producing a mineral or manufacturing a finished product [26].
• Talc–asbestos product liability is the industry's signature legal risk. Talc mined near tremolite can carry trace asbestos, and mass tort litigation has driven talc units into bankruptcy — Imerys Talc America filed Chapter 11 in 2019, and Minerals Technologies placed its Barretts Minerals talc subsidiary into Chapter 11 in October 2023 to resolve 500-plus asbestos-talc suits via a proposed ~$450 million injury trust [27]. Minerals Technologies recorded a $215 million provision in 2025 for estimated funding of current and future talc claims [12]. USGS notes stricter proposed FDA testing protocols for asbestos contamination in talc cosmetics [22].
• Environmental permitting: air permits for particulate (dust) emissions under the Clean Air Act, plus mine permitting, reclamation, and water rules. EPA regulates covered nonmetallic-mineral processing equipment under Clean Air Act New Source Performance Standards, including 40 CFR Part 60 Subpart OOO [28].
• Product/food-safety rules: FDA standards for food- and pharma-grade minerals and filter aids.
• Trade exposure: the U.S. imports most of its barite and is 100% import-reliant for natural graphite, with China the dominant global source — so tariffs, export controls, and geopolitics feed straight into input supply [21][29]. USGS estimated 2025 net-import reliance of 23% for perlite, 25% for vermiculite, and 23% for talc [8][9][22].

8. Competitive dynamics and consolidation

On paper the industry looks only moderately concentrated: the top four firms hold 36.1% of revenue, the top eight 51.8%, the top 50 92.7%, and the Herfindahl-Hirschman Index is 503 — a level the antitrust agencies would call "unconcentrated" [4]. But those national numbers understate real pricing power, because markets here are regional (freight radius) and product-specific. In a given mineral, grade, and freight zone — barite grinding on the Gulf Coast, or fine carbonate within trucking distance of a paint plant — the effective number of competitors can be two or three. Concentration differs sharply by mineral: only six companies process U.S. diatomite, while 53 plants in 29 states expand perlite [7][8].

Consolidation is steady and shaped by two forces: global majors pruning liability-laden or non-core lines (Imerys sold its U.S. carbonate assets to Cimbar in 2022 and has retreated from talc; Minerals Technologies ring-fenced its talc unit in bankruptcy) [18][27], and private equity rolling up the space (Apollo taking U.S. Silica private in 2024) [15]. The direction of travel is more private ownership, more PE, and fewer public pure-plays — the opposite of most maturing industries.

9. Risks

• Cyclicality — exposure to construction, autos, packaging, and drilling means volumes fall in downturns; barite is especially rig-count sensitive [21]. In 2025, Minerals Technologies' specialty-additives sales were hurt by residential construction and paper weakness, while environmental-lining and infrastructure demand grew [12].
• Freight and energy inflation — the whole business model depends on cheap transport and energy; sustained increases compress low-value-to-weight economics [13].
• Product-liability litigation — talc-asbestos and silica claims have already produced bankruptcies and can dwarf the value of the underlying operation [12][27].
• Regulatory tightening — lower silica dust limits raise compliance and capital costs [25].
• Structural demand shifts — graphic-paper decline is a headwind (partly offset by packaging and TiO₂ extension); substitution among fillers is constant [12]. Membrane filters compete with diatomite; silica gel and organic litter compete with absorbent clay; wood fiber competes with perlite in horticulture [7][13][23].
• Import and geopolitical dependence — reliance on foreign barite and Chinese graphite exposes producers to tariffs and supply shocks [21][29].
• Resource depletion / ore quality — the best (whitest, purest, closest) deposits are finite, and a plant is only as good as the rock behind it.
• Incentive risk in emerging applications — renewable-diesel demand for bleaching clay depends partly on government incentives that could change [13].

10. How to invest and the outlook

Public routes (reserve valuation talk for here): direct listed exposure is scarce. Minerals Technologies (NYSE: MTX) is the largest U.S.-listed diversified play — though a large share of its ~$2.1 billion revenue is PCC (a chemicals classification) and it carries the talc-litigation overhang [12][27]. Oil-Dri Corporation (NYSE: ODC) is the closest to a pure-play, with ~$486 million revenue focused on sorbent clays for cat litter, industrial absorbents, and purification products — though its acquired silica-gel business and international operations mean even this is not a perfect NAICS 327992 proxy [13]. Imerys (Euronext Paris: NK) is the way to own the global specialty-minerals leader through a public market, but it trades in Europe and its stock has long reflected talc-liability and portfolio-restructuring discounts [3][14]. U.S. Silica is no longer investable publicly after Apollo took it private in July 2024 [15]. Adjacent, imperfect proxies include U.S. Lime & Minerals (NASDAQ: USLM) for limestone/lime exposure. There is no dedicated ETF; broad materials or small/mid-cap industrial funds hold MTX only as a minor position.

Private routes are where most of this industry actually lives. Omya, Sibelco/Covia, Huber, Carmeuse, and Cimbar are all private or foreign-parented, and private equity is now the dominant new-money model (Apollo/U.S. Silica) [15][17]. For private investors, the practical plays are buying a regional grinder or single-mineral processor outright, backing a PE roll-up of independent operators, or investing alongside a mining owner that also grinds. The scarcity of public options is itself the thesis: attractive, cash-generative deposits change hands in private deals, not on an exchange. The essential diligence is below company level: map each mine and plant to its actual NAICS activity; reconcile tons mined, tons processed, and salable yield; separate commodity from specialty grades; examine delivered freight by customer radius; test energy and utilization sensitivity; review reserve quality and remaining permitted life; identify customer qualification periods and concentration; and allocate environmental, reclamation, silica, and talc liabilities by site.

Outlook (forward-looking judgment): expect low-to-mid single-digit volume growth tied to construction, packaging, and plastics, with value growth skewed to specialty grades — surface-treated, ultrafine, TiO₂-extension, and lightweight-packaging carbonate [11][19]. Barite and other oil-linked volumes will stay volatile with drilling activity [21]. Reshoring of U.S. manufacturing and construction is a modest positive; energy and freight costs are the swing factor on margins, and silica regulation plus talc/silica litigation are the key tail risks. Environmental applications (liners, remediation, water treatment) and renewable-diesel purification are credible secular growth pockets, though the latter carries incentive risk [12][13]. This is not a sector to own for rapid growth. It rewards the patient owner of the right rock in the right place — a defensive, freight-protected, quietly profitable corner of industrial materials where regional density and formulation skill, not scale alone, drive returns.

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Sources

1. NAICS Association, "NAICS Code 327992 — Ground or Treated Mineral and Earth Manufacturing (2022 definition and cross-references)," 2022. https://www.naics.com/naics-code-description/?code=327992
2. U.S. Census Bureau, "2022 NAICS — Sector 31-33 Manufacturing (cross-references and definitions)," 2022. https://www.census.gov/naics/resources/archives/sect31-33.html
3. GlobeNewswire / Research and Markets, "Insights on the Calcite Global Market — Featuring Carmeuse, Sibelco, Huber and Others," 2021. https://www.globenewswire.com/news-release/2021/09/09/2294050/28124/en/Insights-on-the-Calcite-Global-Market-to-2026-Featuring-Carmeuse-Jay-Minerals-and-Sibelco-Among-Others.html
4. U.S. Census Bureau, 2022 Economic Census — Concentration by Largest Firms, NAICS 327992 (receipts $6.45B; 148 firms; CR4 36.1%, CR8 51.8%, CR20 72.6%, CR50 92.7%; HHI 503.2), 2022. https://data.census.gov/profile/327992_-_Ground_or_Treated_Mineral_and_Earth_Manufacturing?n=327992
5. U.S. Census Bureau, County Business Patterns, NAICS 327992 (275 establishments; 10,279 employees; $875.4M annual payroll), 2023. https://www.census.gov/programs-surveys/cbp.html
6. U.S. Small Business Administration, "Table of Small Business Size Standards" (NAICS 327992 = 600 employees), 2023. https://www.sba.gov/document/support-table-size-standards
7. U.S. Geological Survey, "Mineral Commodity Summaries 2026 — Diatomite" (720,000 MT, $420M; 6 companies, 9 facilities; ~60% filtration; price range $10–$1,000+/MT), 2026. https://pubs.usgs.gov/periodicals/mcs2026/mcs2026.pdf
8. U.S. Geological Survey, "Mineral Commodity Summaries 2026 — Perlite" (460,000 MT, $36M; 6 companies, 9 mines, 53 expanding plants; 45% construction, 15% horticulture, 15% filter aids; 23% import reliance), 2026. https://pubs.usgs.gov/periodicals/mcs2026/mcs2026.pdf
9. U.S. Geological Survey, "Mineral Commodity Summaries 2026 — Vermiculite" (2 U.S. producers; 10 companies, 12 exfoliating plants; 25% import reliance), 2026. https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-vermiculite.pdf
10. Future Market Insights, "USA Ground and Precipitated Calcium Carbonate Market" (~$4.8B in 2025), 2025. https://www.futuremarketinsights.com/reports/ground-and-precipitated-calcium-carbonate-industry-analysis-in-the-united-states
11. Market Research Future, "Mineral Fillers Market — Global Report" (North America ~32% share; largest product lines), 2025. https://www.marketresearchfuture.com/reports/mineral-fillers-market-41103
12. Minerals Technologies Inc., 2025 Form 10-K ($2.073B sales; 25.0% production margin; segment operating margins 11.3% C&S, 17.4% ES; $215M talc provision; cyclicality and demand commentary), 2025. https://www.sec.gov/Archives/edgar/data/891014/000089101426000067/form10k.htm
13. Oil-Dri Corporation, 2025 Form 10-K ($485.6M sales; 29.5% gross margin; $64.9M shipping/handling; renewable-diesel commentary; cost risks), 2025. https://www.sec.gov/Archives/edgar/data/74046/000162828025044686/odc-20250731.htm
14. Imerys SA, "Imerys in the USA" (portfolio of talc, carbonates, diatomite, mica, graphite, wollastonite), 2024. https://www.imerys.com/usa
15. PR Newswire / U.S. Silica Holdings, "U.S. Silica to Be Acquired by Apollo Funds for $1.85 Billion" ($15.50/share, delisting), 2024. https://www.prnewswire.com/news-releases/us-silica-enters-into-definitive-agreement-to-be-acquired-by-apollo-funds-for-1-85-billion-302128555.html
16. U.S. Silica Holdings, "Apollo Completes Acquisition of U.S. Silica" (July 2024; 26 operating mines and processing facilities), 2024. https://www.ussilica.com/news-release-7/31/24
17. Covia Corporation / Sibelco, "Calcium Carbonate — HIFILL GCC" (Covia a Sibelco subsidiary; product range), 2024. https://www.coviacorp.com/minerals/calcium-carbonate/
18. CIMBAR Resources, Inc., "CIMBAR Completes Acquisition of Imerys Carbonates USA (Sahuarita, AZ)," 2022. https://cimbarresources.com/cimbar-resources-imerys-arizona-carbonates-acquisition/
19. IndexBox, "Calcium Carbonate Market to 2035 — Surface-Treated and Ultrafine Grades, TiO₂ Extension," 2025. https://www.indexbox.io/blog/calcium-carbonate-market-to-2035-driven-by-surging-demand-for-sustainable-packaging/
20. Minerals Technologies Inc., "Precipitated Calcium Carbonate (PCC) Satellite Plants" (on-site paper-mill model; ~10-year contracts), 2024. https://www.mineralstech.com
21. U.S. Geological Survey, "Mineral Commodity Summaries 2025 — Barite" (>90% used in drilling mud; ~2.3M tonnes sold by grinders in nine states), 2025. https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-barite.pdf
22. U.S. Geological Survey, "Mineral Commodity Summaries 2026 — Talc and Pyrophyllite" (end-use: 36% plastics, 19% paint, 17% ceramics, 12% paper, 8% roofing, 2% rubber; 23% import reliance; FDA testing protocols), 2026. https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-talc.pdf
23. U.S. Geological Survey, "Mineral Commodity Summaries 2025 — Perlite" (wood-fiber substitution in horticulture), 2025. https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-perlite.pdf
24. OSHA, "Respirable Crystalline Silica — General Industry" (PEL 50 µg/m³; action level 25 µg/m³; sorptive-clays exception), 2024. https://www.osha.gov/silica-crystalline/general-industry-info
25. Mine Safety and Health Administration, "Lowering Miners' Exposure to Respirable Crystalline Silica — Final Rule" (PEL 50 µg/m³; effective June 2024), 2024. https://www.msha.gov/silica-final-rule-30-cfr-part-60-resources
26. Mine Safety and Health Administration, "Program Policy Manual — Jurisdiction" (mine vs. mill classification), 2024. https://www.msha.gov/sites/default/files/Directive%20%26%20Guidance/Manuals/PPM%20Vol%20I.pdf
27. Law360 / Minerals Technologies, "Minerals Technologies Puts Barretts Talc Unit Into Bankruptcy" (Chapter 11, Oct. 2023; ~$450M proposed trust), 2023. https://www.law360.com/articles/1728157/minerals-technologies-puts-barretts-talc-unit-into-bankruptcy
28. U.S. Environmental Protection Agency, "Clean Air Act Standards and Guidelines for Mineral Processing" (NSPS 40 CFR Part 60 Subpart OOO), 2024. https://www.epa.gov/stationary-sources-air-pollution/clean-air-act-standards-and-guidelines-mineral-processing
29. U.S. Geological Survey, "Mineral Commodity Summaries 2025 — Graphite (Natural)" (U.S. 100% import-reliant; China-dominated supply), 2025. https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-graphite.pdf