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Carved in Stone
Posted By Brooke Wisdom On April 1, 2010 @ 6:00 am In Articles,Carved In Stone,Departments | No Comments
D is for diamond
Real diamonds are a girl’s best friend, but synthetic ones opened up a whole new world for granite.
By Bill Langer
In last month’s Carved in Stone column, I wandered off on a tangent about our kitchen countertop that is made from Rapakivi granite (aka Baltic Brown). My wife, Pam, says she loves the granite. I told her that inexpensive synthetic diamonds were, in large part, responsible for affordable granite slabs and followed that pronouncement with a short chorus from ‘Diamonds are a girl’s best friend.’
In times past, only the well-to-do could afford the luxury of granite countertops. Hewing granite from solid rock with crude tools and strong backs was so costly that stone was seldom used in any buildings except the finest. Granite became a major industry in the United States only after the introduction of highly efficient tools and reliable power to run them.
In mid-17th through mid-18th century Boston, a few buildings used stone in their construction, but even though the stone could have been obtained locally, it was imported. King’s Chapel, constructed between 1749 and 1754, was the first Colonial New England building constructed with local rock. The granite blocks were fabricated by heating boulders, dropping heavy iron balls on them, and shaping the split stone with hammers.
The birthplace of the American granite industry is generally considered to be the Bunker Hill Quarry, started in 1825 in West Quincy, Mass. Innovations used in that quarry, such as “plug and feathers” to split rock, pulling and hoisting jacks to move blocks within the quarry, and the application of a derrick to lift quarry blocks out of the quarry precipitated fundamental changes in granite quarrying.
The introduction of steam-powered rock drills (c. 1849) spurred the rapidly developing industry, and by the 1870s, there was widespread use of steam quarry drills. Frames called channel bars (patented c. 1887) were used to align drill holes along a line or channel to outline the perimeter of quarry blocks. Jet piercing (using an oxy-fuel flame) was introduced in the early 1900s. The introduction of pneumatic equipment powered by electricity or gasoline added to production capacity, and by about 1920, pneumatic equipment had nearly completely replaced steam. Innovations came fast and furious, further facilitating the job of quarrying.
Enter synthetic diamonds, which were introduced into the stone industry in the 1970s. To manufacture granite countertops nowadays, large quarry blocks are cut from solid rock using synthetic diamond-impregnated beads mounted on steel cable (referred to as wire saws). The blocks are hauled around the quarry with large fork lifts, loaded on trucks, and taken to mills. There, they are cut into slabs using gang saws, wire saws, or circular saws, many of which are also impregnated with synthetic diamonds. Large milling machines shape and polish the granite slab using — you guessed it — synthetic diamonds.
And as we passed the jewelry store display case, Pam informed me that the synthetic diamonds used to create granite countertops are not the type of diamonds that are a girl’s best friend. So now she says she likes granite, but she loves real diamonds.
Author’s note: Production of granite dimension stone in the United States rose to its maximum in 1926; about 700,000 tons. Since that time, granite production has dipped and danced, ending up today at about 500,000 tons per year. And as in Colonial New England, even though granite is available locally, we annually import about 2.25 million tons.
Bill Langer is a geologist with the Mineral Resources Team of the U.S. Geological Survey and can be reached at 303-236-1249 or via e-mail at firstname.lastname@example.org.
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