Essay/Term paper: The classification and formation of crystals

Essay, term paper, research paper:  Science Research Papers

The Classification and Formation of Crystals


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.