Page 8 - Curriculum Visions Dynamic Book

Crystals containing sodium
All the sodium compounds that are now on the surface of the Earth originated in volcanic rocks such as granite. Sodium is present in the white and pink
feldspar crystals in a piece of granite.
When volcanic rocks decompose they release sodium.
Sodium compounds are found in all the freshwater rivers and lakes
of the world in tiny amounts. But when the lake dries out, the sodium compounds are left behind. The most common is the white sparkling mineral (sodium chloride) that we know as common salt, or rock salt.
Crystals of salt are soft and easily scratched. They are mostly white, although they may be tinged
with orange if they have some
iron staining. The crystals are cubic (box-shaped), and are made up of sodium combined with another element, chlorine.
Minerals dissolved in
water are left behind when
it evaporates, leaving salt
deposits. These contain a
variety of compounds, but
they are usually dominated by
sodium chloride. Salt deposits
are common in most deserts and
also in salt marshes near estuaries. Geologists refer to rock salt as “halite”.
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