New Mexico Geological Society Annual Spring Meeting — Abstracts

Perlite is a rhyolitic glass with 2 to 5 wt% total chemical water held within the glass structure. It is often distinguished by the presence of vitreous, pearly luster and "onionskin" perlitic fractures. Occurrences worldwide are associated with Tertiary through middle Quaternary volcanic rocks. Perlite is found the glassy parts of silicic domes and flows, vitric tephra, chill margins of dikes and sills, and welded ash-flow tuffs. Post-emplacement hydration of cooled glass by meteoric water is the principal alteration process, but some hydration by magmatic or meteoric water during or shortly after emplacement, or hydration by water exsolved during cooling may occur. The commercial term perlite includes any volcanic glass that will expand or "pop" when heated quickly to plasticity while evolving steam and forming a lightweight frothy material. The expansion temperature typically ranges from 1400 to 2000°F(760 to 1100°C) and an expanded volume increase of 10 to 20 times compared to the original volume is common.

Perlite is mined by eight companies at 10 operations in six western states. New Mexico accounts for more than 80% of the total tonnage extracted. The remainder comes from Arizona, California, Colorado, Idaho, and Nevada. Dicaperl Corporation, the perlite mining urnt of Grefco, Inc., and Harborlite Corporation are the leading companies, each with two mines. In New Mexico, Dicaperl has mines at Socorro and No Agua Peaks, while Harborlite has one mine in the No Agua Peaks and another near Superior, Arizona. The fourth mine in New Mexico, operated by U.S. Gypsum Company, is on the east flank of East Grants Ridge northeast of Grants.

Most commercial mines, and all New Mexico operations, exploit primarily granular or pumiceous perlite rather than onionskin or "classical" perlite because of the relative uniformity of the ore and the ease of mining with rippers and scrappers. Onionskin perlite is drilled and blasted prior to removal. However, Harborlite and Nord Perlite Co., both near Superior, Arizona, and a small underground mine near Caliente, Nevada, mine classical perlite.

In 1992, domestic production was 571,000 short tons (st), domestic apparent consumption was 591,000 st, and the value of crude perlite was $15.3 million. In 1991, with about the same production and value of crude perlite, the value for expanded perlite was $101.7 million. Perlite exports in 1992, primarily to Canada, were estimated at 30,000 st and imports, from Greece were estimated at 50,000 st. In 1992, 62 plants in 33 states expanded perlite. Only four mines are associated with nearby expansion plants. The others ship crude perlite to captive expansion plants or distributors to commercial plants nationwide. Most shipments are by rail (preferable) or truck (if necessary). Construction uses of expanded perlite accounted for 66% of total domestic sales. Expanded perlite used as filter aid accounted for 15%. All other markets, including use as fillers and in the agricultural markets, accounted for 19%.