Crystal Forms
www.intenseexperiences.com/images/CaveofCrystals2.jpg
Crystal Forms
Minerals grow into specific shapes
They usually crystallize into one of 6 forms
Cubic
Tetragonal
Hexagonal
Orthorhombic
Monoclinic
Triclinic
Axes of Symmetry
• Lines about which a mineral can be
rotated through some angle which
brings the object to a new orientation
which appears identical to its starting
position.
Cubic
• Crystals shaped like
blocks
• 3 axes of symmetry
– All the same length
– All perpendicular to
each other
Cubic Example: Pyrite
http://www.treasuremountainmining.com
Tetragonal
• Crystals shaped like
four-sided prisms and
pyramids.
• Three axes of symmetry
– Two axes are the same
length and lie on a
horizontal plane.
– The third axis is not the
same length and is at a
right angle to the other
two.
– All perpendicular to each
another.
Tetragonal Example: Zircon
www.dkimages.com
Hexagonal
•
Crystals are shaped
like six-sided prisms or
pyramids.
• Four axes of symmetry
– Three lie in the same
plane, are the same
length, and intersect at
120° angles.
– The fourth axis is not the
same length, and is
perpendicular to other
three.
Hexagonal Example: Beryl
www.palagems.com
Orthorhombic
• Crystals are short
and stubby.
• 3 axes of symmetry
– All unequal lengths
– All perpendicular to
each other.
Orthorhombic Example: Topaz
http://www.collectorfinejewelry.com
Monoclinic
• Crystals are short and
stubby with tilted faces
at each end.
• 3 axes of symmetry
– All unequal lengths
– Two axes lie in the same
plane at right angles to
each other.
– The third axis is inclined.
Monoclinic Example: Gypsum
http://www.galleries.com/minerals/property/gyp_flu.gif
Triclinic
• Crystals are usually
flat with sharp
edges, with no right
angles.
• 3 axes of symmetry
– All unequal lengths
– None are
perpendicular to one
another.
Triclinic Example: Feldspar
www.yourgemologist.com
Credits
• http://www.sdnhm.org/kids/minerals/howto
-form.html (information)
• www.gemsociety.org/ wow/read2.htm
(form model images)
• http://www.georgehart.com/virtualpolyhedra/symmetry_axes.html (axes of
symmetry definition
ASSIGNMENT
• PG 63 SHOWS THE SIX MAIN
CRYSTAL SYSTEMS
• YOU NEED TO MAKE 3DEMENSIONAL MODELS OF THE 6
MAIN CRYSTAL SYSTEMS
• MAKE SURE TO LABEL EACH MODEL
WITH THE SYSTEM NAME AND YOUR
NAME