PUMICE AND PUMICITE

Pumice is a volcanic rock formed through the cooling of air-pocketed lava, which results in a highly porous, low-density rock. The low density allows some pumice to float on water. Large pumice rafts, consisting in some instances of thousands of individual pieces of pumice clumped together, are a unique geologic phenomenon and have been documented to be as long as 30 km (19 miles) and to have drifted for several years in oceanic waters. Pumicite is defined as grains, flakes, threads and/ or shards of volcanic glass finer than 4 mm (0.20 in.) in diameter. Pumicite and volcanic ash are descriptive terms that are often used interchangeably. The porous, lightweight properties of pumice are well suited for its main use as an aggregate in lightweight building blocks and assorted building products. Production and prices Mine production of pumice in the United States during 2023 was estimated to be 310 kt (342,000 st), 5 percent more than in 2022. The unit value of pumice was estimated to be $68/t ($62/st) in 2023, 5 percent higher than in 2022. Pumice was produced at 10 operations in California, Idaho, Kansas, New Mexico and Oregon. According to the U.S. Census Bureau, U.S. pumice exports totaled 10.6 kt (11,600 st), 25 percent less than in 2022. Imports totaled 54.8 kt (60,400 st), 47 percent less than in 2022. World resources of pumice are adequate for the foreseeable future. However, transportation costs may encourage the development of deposits closer to markets. Total world production of pumice was estimated to be 18 Mt (20 million st) in 2023, essentially unchanged from 2022. Pumice is used more extensively as a building material outside the United States, which explains the large global production of pumice relative to that of the United States. The top world producers in 2023 were Turkey (8.7 Mt or 9.6 million st), Uganda (1.5 Mt or 1.7 million st), Greece (1 Mt or 1.1 million st), Saudi Arabia (980 kt or 1.1 million st), Algeria (900 kt or 990,000 st) and Ecuador (800 kt or 880,000 st). Processing and consumption Pumice is usually extracted by simple openpit methods using rippers, bulldozers and front-end loaders. Processing typically is limited to drying, crushing and screening, although some abrasive grades may require fine grinding and classification. Lightweight pumice building blocks, the primary use for pumice, may be sawn into a variety of shapes and sizes. In 2023, other major applications included abrasives and horticulture (including landscaping). Minor applications include the use of pumice as an absorbent, as a concrete aggregate and admixture, as a filter aid, and as a traction enhancer for tires. A small percentage of pumice was used in abrasive-type products, including pencil erasers, polishing agents for circuit boards and television monitors, chinchilla chew stones, exfoliants in cosmetics and the removal of henna tattoos, and a variety of heavy-duty hand cleaners. Imports were primarily used as raw material for building blocks (for example, cinderblock) and other lightweight aggregate applications. Several substitutes exist for pumice in agriculture, in horticulture, as an aggregate, as a concrete additive, and in other end products. Outlook Although pumice and pumicite are plentiful in the Western United States, legal challenges and public land designations could limit access to known deposits. Pumice and pumicite production are sensitive to mining and transportation costs, especially from deposits in Western States that are far from major markets. An increase in fuel prices would likely lead to increases in production expenditures and sales prices; imports and competing materials could become attractive substitutes for domestic products. Reference U.S. Geological Survey, 2024, Mineral Commodity Summaries 2024—Pumice and Pumicite: U.S. Geological Survey, p. 140–141, https://pubs.usgs.gov/periodicals/mcs2024/ mcs2024-pumice.pdf

PUMICE AND PUMICITE

Authored by:
R.D. Crangle, Jr.

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To view the past issues of the UCA magazine you must be a member of SME/UCA.

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