Chalking it up to coccoliths

My grandson Donovan is a catcher for the Coyotes, 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 while they had just finished laying down the chalk lines. Seizing the opportunity, I launched into a discussion (perhaps a monologue) 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 skeletons of phytoplankton that rain down on the sea floor from the sunlit waters above. The most important group of chalk-forming phytoplankton are coccolithophores, single-celled marine plants that live in humungous numbers throughout the upper layers of the ocean. Unlike any other plant in the ocean, coccolithophores surround themselves with a microscopic plating made of calcite (limestone). These scales, known as coccoliths, are shaped like hubcaps and are only about five 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 tonnes (or 1.4 billion kilograms) of scales a year. That makes coccolithophores the leading calcite producers in the ocean. I said 1.5 million tonnes very loud!

{{image2-a:r-w:200}}People started to listen again, so I pointed out that the white cliffs of Dover are among 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, plated ware, buttons and similar materials.

One of the chief uses for chalk whiting is making window glazing putty, for which its plasticity, oil absorption and ageing qualities are well suited.

Chalk is also used as a filler, extender or pigment in a wide variety of materials, including ceramics, cosmetics, crayons, plastics, rubber, paper, paints and linoleum. Us old timers remember chalk that was formed into little rods and used for writing on blackboards, or that chalk was dusty. 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 now is made from magnesium carbonate, usually with a few secret additives. Welders’ 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 audience 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!

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