Crystal Systems
Name of
Crystal
System
Wood
Model
#
Description
Typical Forms
(Draw the shape of the
system below)
How many axes _______
Are they the same length____
angles axes intersect at ______
How many axes _______
Are they the same length____
angles axes intersect at
______
All crystals in this system have
four axes. Three of the axes
are the same length and
intersect 60 angles. The
fourth axis is longer or shorter
than the other three.
All crystals in this system have
three axes. Each axis is a
different length. The axes
intersect each other at
90angles.
All crystals in this system have
three axes, each of a different
length. Two of the axes
intersect at 90angles. The
third intersects the others at an
angle greater than 90.
All crystals in this system have
three axes of unequal length
and intersect at angles other
than 90.
Drawings of Faces along Axis
Crystal Systems
Chapter 2 - Properties of Minerals
Introduction
Crystal form is the visible expression of a mineral’s internal arrangement of atoms.
Each of the more than 3800 minerals found on Earth has a distinct crystal form that is the result of the
mineral’s internal arrangement of atoms. These unique forms allow every mineral to be classified into one of
six crystal systems, which are shown on the CRYSTAL SYSTEMS page.
The natural plane surfaces are called crystal faces. The external shape of the crystal depends upon the
geometrical internal arrangement of its atoms and molecules. Through regular alignment of its faces, the basic
crystal pattern is repeated as the crystal grows. Crystal growth in typically in the direction of the axis thus
giving the crystals distinctive shapes. Most of the time, however, minerals compete for space. This crowding
results in an intergrown mass of small crystals. When this occurs the crystal form is not visible to the unaided
eye.
1. Using the CRYSTAL SYSTEMS page provided, complete the chart on the following page.
2. Answer the following questions using your completed results on the Crystal Systems chart.
Comparing and Contrasting. How are minerals in the orthorhombic and monoclinic systems similar?
How do they differ?
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Comparing and Contrasting. Compare and contrast characteristics of minerals in the cubic and
triclinic systems.
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Which system has 4 axes and three of the axes are the same length and intersect at 60-degree angles?
The fourth is either longer or shorter than the other three._____________
Interpreting Diagrams. Study the diagrams in the Data Table. Which system of crystals has three
identical planes of symmetry? Explain your choice.
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