Page 4 - Curriculum Visions Dynamic Book

An element is a substance that cannot be broken down into a simpler substance by any known means. Each of the 92 naturally occurring elements is a fundamental substance from which everything in the Universe is made. This book is about calcium and magnesium
and is one of a series on the elements.
Calcium
Probably everyone has watched a teacher use a stick of “chalk” to mark
a blackboard. Blackboard chalk is a calcium-rich material. It is a compound containing the element calcium, (symbol Ca) bonded together with one other element or more. Calcium on its own is actually a soft, silvery-coloured metal. However, calcium only occurs in nature as part of compounds.
The most common calcium compound
is a material called calcium carbonate.
Most people know calcium carbonate
as rock, such as chalk, limestone and marble. They may have admired coral reefs without realizing that both the coral rock and the tiny green plants that live with the coral, known as algae, have calcium in them. Calcium even contributes to the pearls that are used to make rings and necklaces.
When gardeners use crushed limestone, crushed bone meal, or pulverized shell as a soil-improver in their gardens, few may realise that
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