August 1, 2013
The world of feldspar ebbs and flows with the U.S. construction industry.
By Bill Langer
Our daughter, Kimberly, and son-in-law, Rob, recently remodeled their bathroom and had a beautiful granite countertop installed. As soon as I saw it, I started pointing out all the minerals. Hey, that’s my job.
Many of the minerals were gorgeous feldspars; a group of closely related minerals containing sodium (Na), potassium (K), or calcium (Ca) mixed with aluminum (Al), silicon (Si), and oxygen (O). The numerous types of feldspars blend smoothly into each other, and the final type that forms depends on how much Na, K, or Ca come to the party, and how they bond with the Al, Si, and O.
Determining specific types of feldspars can be complicated and may require heavy-duty lab work. So for general purposes, like pointing out minerals in a countertop, I usually just call it feldspar.
Large-scale feldspar production began in the United States during the 1860s to fill the needs of the New England pottery industry. Feldspar was used in pottery because it gradually melts over a range of temperatures facilitating the melting of clay. It also improves the strength, toughness, and durability of the ceramic body.
At the time, feldspars were hand sorted (cobbed) from pegmatites (bodies of rock consisting of unusually large masses of feldspar, quartz, mica, and other accessory minerals). Most operations were located in the northeastern United States. One notable exception was a sizeable production in North Carolina.
For the first quarter of the 20th century, feldspars were used primarily for ceramics — pottery, sanitary ware, china, and porcelain. Those activities were considered non-essential during World War I, so they had no fuel to run the kilns. After the war, demand was heavier than ever.
Meanwhile, winter weather regularly interrupted feldspar production in the Northeast so, during the 1920s, operations in North Carolina expanded to provide a reliable supply. North Carolina has remained the leading feldspar producing state. Standardization underwent a marked transformation during the 1920s. At the beginning of the decade, feldspar was sold as is. By decade’s end, products had to meet rigid mineral, chemical, and grinding specifications.
By 1930, feldspar found its way into container glass, where it improved the luster of bottles and prolonged the working temperature of the glass. Eventually, sheet glass manufacturers started to use feldspars, and glass manufacturing replaced ceramics as the principal consumer of feldspars. During 1935, the glass industry consumed more than half of the total feldspar production.
Building contracts plummeted during the Great Depression, and feldspar production suffered a 50-percent decrease. But by 1941, recovery from the recession, combined with record glass-container output, resulted in record feldspar production, increased imports, and higher prices.
During 1946, technology revolutionized the feldspar industry. The first commercial flotation plant began operation in North Carolina, which enabled mechanical processing and recovery of feldspars from of a wide variety of granitic rocks. Hand-cobbing nearly became a thing of the past.
Declines in production followed the introduction of aluminum and plastic containers, recycling of glass, and a recent trend to import containers from China. Increases followed the introduction of double pane windows, extensive use of glass in commercial architecture, and use of fiberglass insulation.
These days the feldspar industry dips and dances along with the health of the U.S. construction industry. Industry might expect a boost from the increasing demand for glass used in the production of solar cells.
I spared the kids all this boring stuff. Just as I was going to point out the garnets, my wife, Pam, blurted out “You have some beautiful garnets here.”
Hey! That’s MY job!
Bill Langer is a consulting research geologist who spent 41 years with the U.S. Geological Survey before starting his own business.
He can be reached at Bill_Langer@hotmail.com