(_From Part 15, of Knowledge for the People--Mineralogy and Geology_.)
_Why was crystal so named?_
Because it was probably the first substance ever noticed as occurring in
a regular form, and the ancients believing it to be water permanently
congealed by extreme cold, from its transparency, called it
_Krustallos_, signifying ice; but in time the word became used without
attention being paid to its original meaning, and was applied to all the
regular figures observed in minerals.
_Why are the fine crystals of quartz used as a substitute for glass in
spectacles?_
Because, from their superior hardness, they do not so readily become
scratched as glass: they are then termed pebbles.
_Why is the stone Cairn Gorm so called?_
Because it is found in great beauty in the mountain of Cairn Gorm, in
Scotland. It consists of brown and yellow crystals of quartz, and is
much admired for seal stones, &c.; it is sometimes improperly termed
topaz.
_Why is quartz the constituent of so many gems?_
Because the tinges it receives from metals are sufficient to produce
these varieties. Thus, _amethyst_, or purple quartz, is tinged with a
little iron and manganese.
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