Chalk
Chalk ( /ˈtʃɔːk/) is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores. It is common to find chert or flint nodules embedded in chalk. Chalk can also refer to other compounds including magnesium silicate and calcium sulfate.
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Famous quotes containing the word chalk:
“The women cry,
Come, my fox,
heal me.
I am chalk white
with middle age
so wear me threadbare....”
—Anne Sexton (1928–1974)
“No matter how much faculty of idle seeing a man has, the step from knowing to doing is rarely taken. ‘Tis a step out of the chalk circle of imbecility into fruitfulness.”
—Ralph Waldo Emerson (1803–1882)
“Go, birds of spring: let winter have his fee;
Let a bleak paleness chalk the door,
So all within be livelier than before.”
—George Herbert (1593–1633)