Introduction
Purpose
My purpose of this experiment is to find out how crystals are formed and how they are
classified. For a long time, I've been interested in crystals, so I've decided this
experiment would be perfect for me!
Crystallography
The study of the growth, shape, and geometric characteristics of crystals is called
crystallography. When the conditions are right, each chemical element and compound can
crystallize in a definite and characteristic form.
Thirty-two classes of crystals are theoretically possible, almost all common minerals
fall into one of about twelve classes, and some classes have never been seen. The
thirty-two classes are grouped into six crystal systems, based on the length and position
of the crystal axes. Crystal axes are imaginary lines passing through the center of the
crystals. Minerals in each system share certain proportions and crystal form and many
important optical properties.
The six crystal systems are very important to a mineralogists and geologists;
specification of the system is necessary in the description of each crystal system.
Isometric
This system comprises crystals with three axes, all perpendicular to one another and all
have equal length.
Tetragonal
This system comprises crystals with three axes, all perpendicular to one another; but
only two are equal in length.
Orthorhombic
This system comprises crystals with three mutually perpendicular axes, all of different
lengths.
Monoclinic
This system comprises crystals with three axes, all unequal in length, two o which are
not perpendicular to another, but both of which are perpendicular to the third.
Triclinic
This system comprises crystals with three axes, all unequal in length and is not
perpendicular to one another.
Hexagonal
This system comprises crystals with four axes. Three of these axes are in a single
plane, proportionally spaced, and of equal length. The fourth axis is perpendicular to
the other three. Some crystallographers split the hexagonal in two, calling the seventh
system trigonal or rhombohedral.
Formation of Crystals
Crystals are formed when a liquid becomes solid or when a vapor or liquid solution
becomes supersaturated. Some substances tends to form seed crystal (I grew my crystals
from seed crystals). If a solution like this is cooled slowly, a few seeds grow into
large ones; but if it is cooled rapidly, numerous seeds form and grow only into tiny
crystals. Table salt, purified at a factory by recrystallization, is composed of lots of
cubed crystals, which are barely visible with the naked eye; rock salt, formed in a
really long time, contains enormous crystals of the same cubed form.
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