Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/689568
CARVED IN STONE • 192 CARVED IN STONE 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 M y grandson, Donovan, is a catcher for the Coy- otes, his junior high baseball team, and for the local little league team. Consequently, we get to watch lots of baseball. Recently, we arrived at the Coyotes field early after they had just finished laying down the chalk lines. Seizing the opportunity, I launched into a discussion (perhaps a monolog) about chalk. I caught the attention of a number of folks within earshot by saying that most chalk used to line fields is not actually chalk, but is finely ground marble. Chalk dust is dull whereas marble dust is shiny. I then said that chalk is formed from the microscopic skele- tons of phytoplankton that rain down on the seafloor from the sunlit waters above. The most important group of chalk-forming phytoplankton is Coccolithophores; single-celled marine plants that live in humongous numbers throughout the upper layers of the ocean. Unlike any other plant in the ocean, coccolitho- phores surround themselves with a microscopic plating made of calcite (limestone). These scales, known as coccoliths, are shaped like hubcaps and are only about 5 microns in diameter. For comparison, a human hair is about 100 microns in diameter. Coccolithophores shed scales when they multiply, die, or simply make too many scales. In some places, the ocean waters will turn an opaque turquoise from the dense cloud of coccoliths. I started to lose a few people, so I hit them with my best shot. It is estimated that coccolithophores shed more than 1.5 million tons of scales a year. That makes coccolithophores the leading calcite producers in the ocean. (I said 1.5 million tons very loud.) People started to listen again, so I pointed out that the White Cliffs of Dover are one of the most famous chalk formations. England also boasts the Uffington White Horse, a geoglyph created by cutting into a steep hillside and revealing the underlying chalk. England, as well as France, mines a small amount of this chalk, known in the trade as "whiting," for use as a very mild abrasive for hand polishing nickel, gold, silver, or plated ware, buttons, and similar materials. One of the chief uses for chalk whiting is in making window-glazing putty, for which its plas- ticity, oil absorption, and aging qualities are well suited. Chalk is also used as a filler, extender, or pigment in a wide variety of materials, including ceramics, cosmetics, cray- ons, plastics, rubber, paper, paints, and linoleum. Us old timers remember chalk that was formed into little rods and used for writing on blackboards. That chalk was dusty, and now people use dustless chalk, which is not chalk at all, but is made of gypsum. You might also be surprised to know what other products have replaced chalk. Chalk was used for gymnastics, but it does not behave as desired when exposed to sweat, so gymnastics chalk nowadays is made from magnesium carbon- ate, usually with a few secret additives. Welder's chalk commonly is made of soapstone (talc), which marks like chalk, but will not burn at high cutting temperatures. This list goes on. I was just getting around to telling my dwindling audi- ence that most chalks were deposited in deep, quiet oceans millions of years ago when Blue, the umpire, stole my thunder by hollering out… "PLAY BALL!" P.S. The Coyotes won handily! A baseball field becomes a classroom as fans learn about a microscopic geologic wonder called coccoliths. Chalk One Up for the Geologist Uffington White Horse is a geoglyph created by cutting into a steep hillside and exposing the underlying chalk. Coccolith are microscopic scales formed by single-celled marine plants.